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Pretty Good Privacy™ PGP for Personal Privacy, Version 5.0

1. 1 Co 5 20 97 1024 1024 E O Philip R Zimmermann lt prz acm o Em Ese 5 20 93 1024 E mc e ino 46005415040 Y Double keys represent the private and public key pairs you have created for yourself and single keys represent the public keys you have collected from others If you have more than one type of key you will notice that RSA type keys are blue and DSS Diffie Hellman keys are yellow By double clicking on any of the keys you can expand the entries to reveal the user ID and e mail addresses for the owner of the key as represented by the figure icons By double clicking a figure icon you can see the signatures of any users who have certified the key as represented Chapter 5 Managing Keys And Setting by the quill icon If you don t want to double click down through the various levels of information for each key simply select the keys of interest and then choose Expand Selection from the Edit menu PGPkeys Attribute Definitions Along the top of the window are labels that correspond to the attributes associated with each key Keys Validity Trust Shows an iconic representation of the key along with the user name and e mail address of the owner Indicates the level of confidence that the key actually belongs to the alleged owner The validity is based on who has signed the key and how well you trust the signer s to vouch for the authenticity of a key The pub lic keys you sign yourself have the highe
2. 0 ccc cece een 112 Exposure on Multi user SUSIONIS cheesy ka ERO RR EROR REO RR ERR E pin 114 TRATHCADGWES esedesdaecketrd eed REX RES eese ques EE dra due qa 114 CRT BIAIS a oa i do p CEU d CEN EG Fr Edd Ou d CES IC oM CR S ES s 114 PGP for Personal Privacy Version 5 0 User s Guide for Windows Recommended Introductory Readings 0 cece eee 115 Oher Reading M rS 116 A Gloss ry of TeMi ev s 4RAWRXANRRRWWRZNREXRAVEERRERPRRRRPRPER 117 DOER cere tr TT re Teter ee E RE RR 0 D e 121 Contents Chapter 1 Introducing PGP for Personal Privacy With PGP for Personal Privacy you can easily protect the privacy of your email messages and file attachments by encrypting them so that only those with the proper authority can decipher the information You can also digitally sign the messages and files you exchange which ensures that they have come from the person who allegedly sent them and that the information has not been tampered with in any way while in transit The most convenient way to use PGP is through one of the popular email applications supported by the plug ins This allows you to encrypt and sign as well as decrypt and verify your messages while you are composing and reading your e mail In addition if you are communicating with another PGP user who is using an email application that adheres to the PGP MIME standard you can perform all of the PGP functions on both your messages and any file attachments by simpl
3. Congratulations You have just generated a PGP key pair You will now be able to receive secure messages and sign documents If you wish to send your key to the server at a later date simply right click on it in PGPkeys and select Keyserver Send Selected Keys Click Finish below to add your new key to your keyring 17 Click Finish A pair of keys representing your newly created keys appears in the PGPkeys window You will notice that the older RSA keys are blue and the newer DSS Diffie Hellman keys are yellow At this point you can examine your keys by checking their properties and the attributes associated with the keys you may also want to add other user names or e mail addresses See Chapter 5 for complete details on how to add a new user name 32 Chapter 3 Making and Exchanging Keys Protecting Your Keys Once you have generated a key pair itis wise to create a spare set and put them in a safe place in case something happens to the originals In fact when you close the PGPkeys window after creating a new key pair you are prompted to save a backup copy PGPkeys x The new key that has been generated during this session is very important Losing your key file in a disk crash or accidental file deletion without having a backup will render the key and all data encrsaed with that key useless It is strongly recommended that your backup your key to a medium other than your main drive Your private k
4. Corporate Key 6 3 97 1024 2048 Qe Will Price lt wprice pgp com gt 6 3 97 1024 4000 c E RE EE R8 FE E 6 EE 8 ER f 2 Choose New Key option from the Keys menu PGP for Personal Privacy Version 5 0 User s Guide for Windows The Key Generation Wizard provides some introductory information on the first screen Key Generation Wizard In order for other people to send you secure messages you must generate a key pair Your key pair will also be used to sign digital documents key pair consists of a Public Key and a Private Key The public key should be given td everyone you know PGP has facilities to assist in this Th private key should be kept absolutely secret If you would like more information on what a key pair is and how PGP works click the Help button below Otherwise choose Next to continue 3 When you are through reading this information click Next to advance to the next dialog box The Key Generation Wizard then asks you to enter your user name and e mail address Key Generation Wizard What name and email address should be associated with this key pair By listing your name and email address here you let your correspondents know that the key they are using belongs to you Eull name Aa Email address Chapter 3 Making and Exchanging Keys 4 Enter your name on th
5. Keep a trusted backup copy of your public keyring and your private key on write protected media Since your own trusted public key is used as a final authority to directly or indirectly certify all the other keys on your keyring it is the most important key to protect from tampering You may wish to keep a backup copy on a write protected floppy disk PGP generally assumes that you will maintain physical security over your system and your keyrings as well as your copy of PGP itself If an intruder can tamper with your disk then in theory he can tamper with the program itself rendering moot the safeguards the program may have to detect tampering with keys One somewhat complicated way to protect your own whole public keyring from tampering is to sign the whole ring with your own private key You could do this by making a detached signature certificate of the public keyring How Does PGP Keep Track of Which Keys are Valid Before you read this section you should read the previous section on How to Protect Public Keys from Tampering PGP keeps track of which keys on your public keyring are properly certified with signatures from introducers that you trust All you have to do is tell PGP which people you trust as introducers and certify their keys yourself with your own ultimately trusted key PGP can take it from there automatically validating any other keys that have been signed by your designated introducers And of course you may
6. Michael lannamico lt mji pgp com gt L2 x General Key ID oxCDAB5B0D Created 5 2 37 Key Type RSA Expires Never Trust Model Validity Complete Invalid X BEEENEN Valid Untrusted J Trusted Trust Ultimate z Implicit Trust rm Fingerprint 96 D D651 4447 B046 D3FA 93C0 S1DB BOBF M Enable Change Passphrase Cancel Help A unique identifying number associated with each key This identification number is useful for distinguishing between two keys that share the same user name and e mail address The date when the key was created The key type This is either RSA or DSS Diffie Hell man The date when the key expires The owner specifies this date when they create their keys and the value is usu ally set to Never However some keys are set to expire on a particular date if the owner only wants them to be used for a limited period of time Indicates the validity of the key based on its certifica tion and the level of trust you have in the owner to vouch for the authenticity of someone else s public key You set the trust level by sliding the bar to the appropri Chapter 5 Managing KeysAnd Setting ate level Complete Marginal or Untrusted The bar is not shown for revoked expired and implicitly trusted keys Fingerprint A unique identification number that is generated when the key is created and is the primary means by which you can check the authenticity of a key
7. The new PGP 5 0 software you install will install the newer versions of those files for you Click on OK to complete the uninstallation and dismiss the Add Remove panel when complete Install the new PGP 5 0 software using the provided InstallShield utility It s recommended but not mandatory to direct the installer to the default install directory When the installer asks you if you have existing keyrings click on yes locate your old PGP 5 0 keyrings and follow the instructions to copy those keys to your new PGP 5 0 keyrings PGP for Personal Privacy Version 5 0 User s Guide for W indows 11 10 Restart your computer You can now run the new PGP 5 0 software Installing PGP To Install PGP from a CD ROM l Start Windows 2 Insert the CD ROM 3 Run the Setup program 4 Follow the on screen prompts To Install PGP from PGP s Web site 1 Download the PGP program onto your computer s hard drive 2 Double click the PGP installation program icon 3 Follow the on screen prompts Running PGP PGP works on the data generated by other applications As such the appropriate PGP functions are designed to be immediately available to you based on the task you are performing at any given moment There are three primary ways to use PGP From the System tray From within supported e mail applications From the Windows Explorer File menu Chapter 2 Getting Started Using PGP from the Sys
8. and then click OK The new name is added to the end of the user name list associated with the key If you want to set the new user name and address as the primary identifier for your key then select the name and address and click on the Set As Primary User ID command Checking a Key s Fingerprint It is often difficult to know for sure that a key belongs to a particular individual unless that person physically hands their key to you on a floppy disk Since exchanging keys in this manner is not usually practical especially for users who are located many miles apart you can rely on the unique fingerprint associated with each key to verify that a key does indeed belong to the alleged owner There are several ways to check a keys fingerprint but the safest is to make a call to the person and have them read the fingerprint to you over the phone It is highly unlikely that someone will be able to intercept this random call and imitate the person on the other end You can also compare the fingerprint on your copy of someone s public key to the fingerprint listed for their original key on a public server To check a key s fingerprint l Select the key for the fingerprint you want to check 2 Choose Key Properties from the Keys menu 3 Note the fingerprint and compare it to the original PGP for Personal Privacy Version 5 0 User s Guide for W indows 65 Signing Someone s Public Key When you create a set of keys they are automatically s
9. authenticity of another users key See Chapter 5 for more details 6 Click OK PGP for Personal Privacy Version 5 0 User s Guide for W indows 47 48 If you have elected to sign the message the PGP Signing Passphrase dialog box appears requesting your personal passphrase for your default private key If you have other key pairs and you want to use one of those instead you can click on the arrow and select the appropriate key PGP Signing Passphrase MEI Signing key Michael J lannamico lt mji pgp com gt Enter passphrase Iv Hide Typing I a Cancel Enter your passphrase and then click OK Return to your e mail application and choose the Paste command from the Edit menu This will copy the encrypted message back into your e mail application 9 Send your e mail to the intended recipient s Encrypting and Signing from the Windows Explorer If you plan to send an encrypted file as an attachment with your e mail message or if you just want to encrypt a file to protect it on your own computer you do so from the Windows File Explorer To encrypt and sign from the Windows Explorer l 2 Open the Windows Explorer from the Start menu Select the file or files that you want to encrypt You can select multiple files but you must encrypt and sign each of them individually Chapter 4 Sending and Receiving Private E mail 3 Choose the desired option from the File menu or from the pop up menu whi
10. however it is believed to be computationally infeasible for an attacker to devise a substitute message that would produce an identical message digest The message digest gets encrypted by the sender s private key creating a digital signature of the message Figure 5 shows how a digital signature is generated Chapter 6 Security Features and Vulnerabilities Figure 5 Digital Signature Generation Message ITIIIT Document IITIIT Fi E Confidential Sent to Recipien Eneryption Message E Digital Digest Signature r Message Digest Algorithm Sender s Private Ke The recipient or anyone else can verify the digital signature by using the sender s public key to decrypt it as shown in Figure 6 This proves that the sender was the true originator of the message and that the message has not been subsequently altered by anyone else because the sender alone possesses the private key that made that signature Forgery of a signed message is not feasible and the sender cannot later disavow his signature PGP for Personal Privacy Version 5 0 User s Guide for W indows 93 94 Figure 6 Digital Signature Verification Received From Sender Message Digest Document Algorithm Locally Generated Band mmn Riche order Message Digest LL Digital Signature 6100000101 000011 Recovered od Message Digest X opa Sender
11. the methods for exchanging protecting and authenticating keys Chapter 4 Sending and Receiving Private E mail Explains how to send and receive email messages and file attachments depending on the type of email application you and the recipients of your email are using Chapter 5 Managing Keys And Setting Preferences Explains how to examine and alter a key s attributes and how to establish preferences for the PGP program Chapter 6 Security Features and Vulnerabilities This chapter is provided by Phil Zimmermann and describes the basic concepts behind public key encryption and elaborates on some of the vulnerabilities PGP for Personal Privacy Version 5 0 User s Guide for W indows Chapter 1 Introducing PGP for Personal Privacy Chapter 2 Getting Started This chapter explains how to run PGP and provides a quick overview of the procedures you will normally follow in the course of using the product Based on this information you will have a fairly good understanding of how to use PGP which should be especially appreciated by those who don t want to read through the entire manual before beginning to use the product System Requirements Windows 95 or NT 8 MB RAM 15 MB hard disk space Compatibility with Other Versions PGP has gone through many revisions since it was released by Phil Zimmermann as a freeware product in 1991 and it is estimated that there are now over 2 million copies in circulation Although this version o
12. In the secure telephone arena your choices look bleak The leading contender is the STU III Secure Telephone Unit made by Motorola and AT amp T for 2000 3000 and used by the government for classified applications It has strong cryptography but requires some sort of special license from the government to buy this strong version A commercial version of the STU III is available that is watered down for NSA s convenience and an export version is available that is even more severely weakened Then there is the 1200 AT amp T Surity 3600 which uses the government s famous Clipper chip for encryption with keys escrowed with the government for the convenience of wiretappers Then of course there are the analog non digital voice scramblers that you can buy from the spy wannabe catalogs that are really useless toys as far as cryptography is concerned but are sold as secure communications products to customers who just don t know any better In some ways cryptography is like pharmaceuticals Its integrity may be absolutely crucial Bad penicillin looks the same as good penicillin You can tell if your spreadsheet software is wrong but how do you tell if your cryptography package is weak The ciphertext produced by a weak encryption algorithm looks as good as ciphertext produced by a strong encryption algorithm There s a lot of snake oil out there A lot of quack cures Unlike the patent medicine hucksters of old these software implementors
13. Kk 7 1wQx4k l1Tv68hKIqieGqnLonNUvQrPKZyv2B kQ4WaFZxxZ5b5Cel7uNJDI Ehp996nf2jnz67xkhdv3anXNOD026s4m3gTXWUEABRGOIKlpYZhhZWwgsSi4gSWFu bnFtaUNvIDxtamlAcGdwLmNvbT6JARUDBRAzXlblGs4m3gTXWWEBASPlB 4xAf G H USRbq6XMxMvMVYNdVHgl 2bU9AGAJKwM TShn cq Lj8VMpOMN1XzZuXVjxQ5Ln ZHSgNACXtsA sqCVd7xsXjJIG72i cbio0jt54xQJHVsQ mOm8YHIc67qgobW5G03i uqjDrHrB3Plc 4CwtFPTcE6mkfLYoKorZ GAPpJVbrpEAm3Fhs20 gDUCSNvogKzv DOElXO0co6RQmzM7BMT3kDZe 44U0p J Sx TBEXzpARXBCGEVXcQOSVXFIbA oDdJSE qLd OckGunw312Nfd fvGv5MKdvatd dsdz0K 7 5xH3YHmOrpB QUPSgMB nnnhcLP ZXlJbW NcxXVOVS9riQEVAwUQMw n4TP6oFKZLSUbAQEk7gf IKstvUhaBL9BRbF9 RbMjeSbdiHCEt8KRx0A912 4IZGZckYZrypBP7A3mPOtFs6MQUDS A4fb5locId8 38G6i0IjEvw Uu2VBCZbZTR74PwuHjc6nzdSMvq0lT6rqL4SidCxwskaAvEaf9qkK GbllapJFlG3qgzk2dgsvKhZ6pAohDSNTvol3xj4aELZxATwcbjqgvlhxquaYkUYjHDc i3TyelrEpkaJ5qJwEMXSHTnJRsvjXlpMI IOEaZmr Dk4AFbstRHwHZPbhRRkJtZ q8Czn3F5UszkWaFjwMSaeTLt Y2qtEwjnErct60IZAS8Je IDoktvl9Xo0n20EUxj iUw HIkAlQMFEDMOF4dleYS4x6lm3QEBej0D lbJLL3Kuek9rO K fwUdIRx TZyV BUo3JCpiO EZVF7Vhzo3GOWMuNYNSwnSoMMgsdgyB8q WsPIdnugL4XpGlicvNLBP 7Fbuw4iUNScoxXF QPl6RQ60sUuf9r S3X3Qdcu39HhIzzzZVLYks c 6AvxtdMOuO0T tzqpcg d c 3RSmlUlm pz 6 Getting Public Keys from a Key Server If the person to whom you want to send encrypted mail is an experienced PGP user chances are that they have placed a copy of their public key ona key server This makes it very convenient for you to get a copy of their most up to date key whenever you want to
14. Version 5 0 or later have information embedded in them that tells a sender what block ciphers are understood by the recipient s software so that the sender s software knows which ciphers can be used to encrypt DSS Diffie Hellman public keys will accept CAST IDEA or triple DES as the block cipher with CAST as the default selection At present for compatibility reasons RSA keys do not provide this feature Only the IDEA cipher is used by PGP to send messages to RSA keys because older versions of PGP only supported RSA and IDEA Data Compression PGP normally compresses the plaintext before encrypting it because it s too late to compress the plaintext after it has been encrypted encrypted data is incompressible Data compression saves modem transmission time and disk space and more importantly strengthens cryptographic security Most cryptanalysis techniques exploit redundancies found in the plaintext to crack the cipher Data compression reduces this redundancy in the plaintext thereby greatly enhancing resistance to cryptanalysis It takes extra time to compress the plaintext but from a security point of view it s worth it Chapter 6 Security Features and Vulnerabilities Files that are too short to compress or that just don t compress well are not compressed by PGP In addition the program recognizes files produced by most popular compression programs such as PKZIP and does not try to compress a file that has already been comp
15. create and manage your keys and access all of the functions for encrypting and signing as well as decrypting and verifying your email messages and file attachments The following section provides a quick run through of the procedures you normally follow in the course of using PGP For details concerning any of these procedures refer to the appropriate chapters in this book where they are fully explained Create a Private and Public Key Pair Before you can begin using PGP you need to generate a key pair consisting of a private key to which only you have access and a public key that you can copy and make freely available to everyone with whom you exchange email You have the option of creating a new key pair immediately after you have finished the PGP installation procedure or you can do so at any time by opening the PGPkeys window Exchange Public Keys with Others After you have created a key pair you can begin corresponding with other PGP users To do so you will need a copy of their public key and they will need a copy of your public key Since your public key is just a block of text it is really quite easy to trade keys with someone You can either include your public key in an email message copy it to a file or you can post it on a public key server where anyone can get a copy when they need it Certify and Validate Your Keys Once you have a copy of someone s public key you can add it to your public keyring You should then chec
16. directly sign more keys yourself There are two entirely separate criteria PGP uses to judge a public key s usefulness don t get them confused 1 Does the key actually belong to whom it appears to belong In other words has it been certified with a trusted signature 2 Does it belong to someone you can trust to certify other keys PGP for Personal Privacy Version 5 0 User s Guide for W indows 99 100 PGP can calculate the answer to the first question To answer the second question you must tell PGP explicitly When you supply the answer to question 2 PGP can then calculate the answer to question 1 for other keys signed by the introducer you designated as trusted Keys that have been certified by a trusted introducer are deemed valid by PGP The keys belonging to trusted introducers must themselves be certified either by you or by other trusted introducers PGP also allows for the possibility of you having several shades of trust for people to act as introducers Your trust for a key s owner to act as an introducer does not just reflect your estimation of their personal integrity it should also reflect how competent you think they are at understanding key management and using good judgment in signing keys You can designate a person as untrusted marginally trusted or completely trusted to certify other public keys This trust information is stored on your keyring with their key but when you tell PGP to copy a key off your key
17. easiest way to decrypt and verify the e mail sent to you is with an application supported by the PGP plug ins Although the procedure varies slightly between different e mail applications when you are using an e mail application supported by the plugins you can perform the decryption and verification process by clicking a button in your application s toolbar In addition if you are using an application that supports the PGP MIME standard you can decrypt and verify your e mail messages as well as any file attachments by just clicking an icon attached to your e mail If you are using an e mail application that is not supported by the PGP plug ins you will decrypt and verify your e mail messages via the Windows clipboard In addition if your e mail includes encrypted file attachments you must decrypt them separately from the Windows Explorer Decrypting and Verifying from Supported e mail Applications If you are communicating with other PGP users and they have encrypted and signed their mail using the PGP MIME standard an opened envelope icon will appear when you open your e mail X Sender nji mail pgp com Unverified X Mailer QUALCOMM Windows Eudora Pro Version 3 0 2 b4 32 Date Wed Zl May 1997 10 02 32 0700 To mjilipqp com From Mike Iannamico lt mjifpgp com gt Subject test ER Decrypt PGP MIME Message In this case you can decrypt and verify the message and any attached files by simply double clicking this ico
18. ins that adheres to the PGP MIME standard and you are communicating with another user who s e mail application also supports this standard both of you can automatically encrypt and decrypt your e mail messages and any attached files when you send or retrieve your e mail All you have to do is turn on the PGP MIME encryption and signatory functions from the PGP Preferences dialog box When you receive e mail from someone who uses the PGP MIME feature the mail arrives with an attached icon indicating that it is PGP MIME encoded X Sender mjif mail pgp com Unverified X Mailer QUALCOMM Windows Eudora Pro Version 3 0 2 b4 32 Date Wed 21 May 1997 10 02 32 0700 To mjifpgp com From Mike Iannamico mjilipgp com Subject test Decrypt PGP MIME Message Chapter 2 Getting Started All you need to do in order to decrypt the text and file attachments in PGP MIME encapsulated e mail and to verify any digital signatures is to double click the opened envelope icon Using PGP from the Windows Explorer You can encrypt and sign or decprypt and verify files such as word processing documents spreadsheets and video clips directly from the Windows Explorer If you are not using an e mail application such as Eudora that adheres to the PGP MIME standard you must use this method to attach files you want to send along with your e mail messages In some cases you might even want to encrypt and decrypt files that you store on your own compu
19. it to a diskette and then physically hand it to you Since you are not always within close enough proximity to personally hand a disk to someone you will generally exchange public keys via e mail or get them from a public key server Even though these are somewhat less secure methods of exchanging tamper proof keys you can still determine if a key really belongs to a particular person by checking its digital fingerprint a unique series of numbers generated when the key is created By comparing the fingerprint on your copy of someone s public key against the fingerprint on their original key you can be absolutely sure that you do in fact have a valid copy of their key The most definitive way to check a key s fingerprint is to call the person and have them read their fingerprint over the phone When you get a key from a public key server you don t have to go through this exercise but can instead access the fingerprint information for the key while you are on line Of course you do this with the expectation that the person periodically checks their key to make sure that no one has switched their key Once you are absolutely convinced that you have a legitimate copy of someone s public key you can then sign their key By signing someone s public key with your private key you are signifying to the world that you are sure the key belongs to the alleged user For instance when you create a new key it is automatically certified with your own d
20. monolithic institutions such as Internet Privacy Enhanced Mail PEM which are Chapter 6 Security Features and Vulnerabilities based on centralized control and mandatory centralized trust The standard schemes rely on a hierarchy of Certifying Authorities who dictate who you must trust The program s decentralized probabilistic method for determining public key legitimacy is the centerpiece of its key management architecture PGP lets you alone choose who you trust putting you at the top of your own private certification pyramid PGP is for people who prefer to pack their own parachutes Note that while this decentralized grass roots approach is emphasized here it does not mean that PGP does not perform equally as well in the more hierarchical centralized public key management schemes Large corporate users for example will probably want a central figure or person who signs all the employees keys PGP handles that centralized scenario as a special degenerate case of PGP s more generalized trust model How to Protect Private Keys from Disclosure Protect your own private key and your passphrase very carefully If your private key is ever compromised you d better get the word out quickly to all interested parties before someone else uses it to make signatures in your name For example they could use it to sign bogus public key certificates which could create problems for many people especially if your signature is widely trusted An
21. most resourceful government intelligence agencies I felt so smug about my achievement Years later I discovered this same scheme in several introductory cryptography texts and tutorial papers How nice Other cryptographers had thought of the same scheme Unfortunately the scheme was presented as a simple homework assignment on how to use elementary cryptanalytic techniques to trivially crack it So much for my brilliant scheme From this humbling experience I learned how easy it is to fall into a false sense of security when devising an encryption algorithm Most people don t realize how fiendishly difficult it is to devise an encryption algorithm that can withstand a prolonged and determined attack by a resourceful opponent Many mainstream software engineers have developed equally naive encryption schemes often even the very same encryption scheme and some of them have been incorporated into commercial encryption software packages and sold for good money to thousands of unsuspecting users This is like selling automotive seat belts that look good and feel good but snap open in even the slowest crash test Depending on them may be worse than not wearing seat belts at all No one suspects they are bad until a real crash Depending on weak cryptographic software may cause you to unknowingly place sensitive information at risk You might not otherwise have done so if you had no cryptographic software at all Perhaps you may never even disco
22. nut Do law abiding citizens have any need to encrypt their e mail What if everyone believed that law abiding citizens should use postcards for their mail If a nonconformist tried to assert his privacy by using an envelope for his mail it would draw suspicion Perhaps the authorities would open his mail to see what he s hiding Fortunately we don t live in that kind of world because everyone protects most of their mail with envelopes So no one draws suspicion by asserting their privacy with an envelope There s safety in numbers Analogously it would be nice if everyone routinely used encryption for all their e mail innocent or not so that no one drew suspicion by asserting their e mail privacy with encryption Think of it as a form of solidarity Until now if the government wanted to violate the privacy of ordinary citizens they had to expend a certain amount of expense and labor to intercept and steam open and read paper mail Or they had to listen to and possibly transcribe spoken telephone conversation at least before automatic voice recognition technology became available This kind of labor intensive monitoring was not practical on a large scale This was only done in important cases when it seemed worthwhile Senate Bill 266 a 1991 omnibus anti crime bill had an unsettling measure buried in it If this non binding resolution had become real law it would have forced manufacturers of secure communications equipment to insert sp
23. point on However under certain conditions you may want to create a special set of keys that you plan to use for only a limited period of time In this case when the public key expires it can no longer be used by someone to encrypt mail for you but it can still be used to verify your digital signature Similarly when your private key PGP for Personal Privacy Version 5 0 User s Guide for W indows 27 expires it can still be used to decrypt mail that was sent to you before your public key expired but can no longer be used to sign mail for others 11 Click Next to advance to the next dialog box The Key Generation Wizard asks you enter a passphrase Key Generation Wizard Your private key will be protected by a passphrase It is important that you do not write this passphrase down so it needs to be easy to remember We recommend that your passphrase be at least eight characters long and contain at least one non alpyabetic character e7 M Hide Typing Passphrase I n AM Passphrase Confirmation a 4 4 lt a a y Dn Da n lt o taa Heo 12 In the Passphrase entry box enter the string of characters or words you want to use to maintain exclusive access to your private key To confirm your entry press the Tab key to advance to the next line then enter the same passphrase again Normally as an added level of security the characters you enter for the passphrase do not appear on t
24. revoke their keys when they are no longer valid or have been compro 9 mised in some way A key with a red X through itindicates a key that is invalid A key with a clock indicates that the key has expired A key s expiration date is established when the key is created A smiley face represents the owner of the key and lists the user names and e mail addresses associated with the key A quill indicates the signatures from those PGP users who have vouched for the authenticity of the key A signature with a red line through it indicates a A revoked signature A signature with a red X through it indicates a bad or invalid signature An empty bar indicates an invalid key or an untrusted user Eug A half filled bar indicates a marginally valid key or marginally trusted user HE A full bar indicates a completely valid key or a completely trusted user A striped bar indicates an implicitly valid key and implicitly trusted key This setting is only available for the private and public key pairs you create PGP for Personal Privacy Version 5 0 User s Guide for W indows 61 62 Examining a Key s Properties In addition to the general attributes shown in the PGPkeys window you can also examine and change other key properties To access the properties for a particular key select the desired key and then choose Key Properties from the Keys menu Key ID Created Key Type Expires Trust Model
25. secure general purpose encryption software available in the US I m not as certain about the security of PGP as I once was about my brilliant encryption software from college If I were that would be a bad sign But I don t think PGP contains any glaring weaknesses although I m pretty sure it contains bugs I have selected the best algorithms from the published literature of civilian cryptologic academia For the most part they have been individually subject to extensive peer review I know many of the world s leading cryptographers and have discussed with some of them many of the cryptographic algorithms and protocols used in PGP It s well researched and has been years in the making And I don t work for the NSA But you don t have to trust my word on the cryptographic integrity of PGP because source code is available to facilitate peer review And one more point about my commitment to cryptographic quality in PGP Since I first developed and released PGP for free in 1991 I spent three years under criminal investigation by US Customs for PGP s spread overseas with risk of criminal prosecution and years of imprisonment by the way you didn t see the government getting upset about other cryptographic software it s PGP that really set them off what does that tell you about the strength of PGP I have earned my reputation on the cryptographic integrity of my products I will not betray my commitment to our right to privacy for which
26. send them If you are communicating with someone who does not have a PGP MIME compliant e mail application you should encrypt your e mail with PGP MIME turned off to avoid any compatibility problems The drawback with this method is that you will have to separately encrypt any file attachments you want to send with the e mail NOTE Ifyou do not send your e mail immediately but instead temporarily store it in your outbox you should be aware that when using some e mail applications the information will not be encrypted until the e mail is actually transmitted Before queuing encrypted messages you should check to see if your application does in fact encrypt the messages in your outbox If it does not you might want to consider encrypting the message via the clipboard before queuing it in the outbox To encrypt and sign with supported e mail applications l Use your e mail application to compose your e mail message just as you normally would 2 When you have finished composing the text of your e mail message specify whether you want to encrypt and sign the text of your message by clicking the lock and quill buttons 2 el e If you are communicating with another PGP user who is using an e mail application that adheres to the PGP MIME standard you will want to click on the PGP MIME button When you click one of these buttons they remain indented to indicate the operations you want to perform NOTE Ifyou know that you are goin
27. skr file 57 R random numbers 91 receiving private email 43 revoking keys 72 RSA 114 116 RSA technology keys 8 creating 25 running PGP 12 13 S saving keys 33 34 secring skr file 57 security breach 112 sending private email 43 setting passphrase for a key 28 preferences 74 signing deleting signatures 69 email 4 43 checking signature 2 from W indows Explorer 48 50 overview 2 via the Clipboard 46 48 keys 66 public keys 66 96 using Eudora 43 46 storing keys 33 34 system requirements 7 System tray PG P for Personal Privacy Version 5 0 User s Guide for Windows 125 using PGP from 13 T traffic analysis 114 trust granting for key validations 67 Trust Model property 62 trusted introducer 97 100 U upgrading from a previous version of PGP 8 from ViaCrypt 8 user ID 97 user name adding 64 using PGP 12 from the Clipboard 13 from the System tray 13 V validating keys granting trust for 67 public keys 3 validity checking a key s 40 verifying authenticity of a key 40 email 4 from others 51 from W indows Explorer 54 56 via the Clipboard 53 within Eudora 51 52 versions of PGP compatible 7 upgrading to new 8 ViaCrypt upgrading from 8 viewing 126 attributes of keyrings 58 63 key attributes 14 private and public key pairs 14 virus 110 W W indows system requirements 7 W indows Explorer decrypting file attachments 54 decrypting from 54 56 encr
28. take to perform the decryption and encryption process You will need to strike a balance between the convenience of performing PGP functions quickly with a smaller key and the increased level of security provided by a larger key Unless you are exchanging extremely sensitive information that Chapter 3 Making and Exchanging Keys is of enough interest that someone would be willing to mount an expensive and time consuming cryptographic attack in order to read it you are safe using a key composed of 1024 bits NOTE When creating a DSS Diffie Hellman keys the size of the DSS por tion of the key is increased in fixed increments and is less than the size of the Diffie Hellman portion of the key and is limited to a max imum size of 1024 bits 9 Click Next to advance to the next dialog box The Key Generation Wizard asks you to indicate when the key pair should expire Key Generation Wizard lt is possible to create a key that will expire in a fixed number of days Note that this cannot be changed later For most applications it is recommended that you generate a key which never expires toa ee 10 Indicate when you want your keys to expire You can either go with the default selection which is never or you can enter a specific number of days after which the keys will expire Once you create a key pair and have distributed your public key to the world you will probably continue to use the same keys from that
29. that you need to generate keys or otherwise use the RSA algorithm see the ven dor from whom you bought your PG P product A Quick Overview PGP is based on a widely accepted encryption technology known as public key cryptography in which two complementary keys are used to maintain secure communications One of the keys is a private key to which only you have access and the other is a public key which you freely exchange with other PGP users Both your private and your public keys are stored in keyring files which are accessible from the PGPkeys window in which you perform all your key management functions To send someone a private email message you use a copy of that person s public key to encrypt the information which only they can decipher by using their private key Conversely when someone wants to send you encrypted mail they use a copy of your public key to encrypt the data which only you can decipher by using a copy of your private key You also use your private key to sign the email you send to others The recipients can then use their copy of your public key to determine if you really sent the email and whether it has been altered while in transit When someone sends you email with their digital signature you use a copy of their public key to check the digital signature and to make sure that no one has tampered with the contents Chapter 1 Introducing PGP for Personal Privacy With the PGP program you can easily
30. the key has been in use for a while it is less likely that someone will try to replace it because there are many other copies in circulation Shows the number of bits used to construct the key Generally the larger the key the less chance that it will ever be compromised However larger keys require slightly more time to encrypt and decrypt data than do smaller keys When you create a DSS Diffie Hellman key there is one number for the DSS portion and another number for the Diffie Hellman portion PGPkeys Icon Definitions The following table shows all of the mini icons used in the PGPkeys win dow along with a description of what they represent ICONS WHAT THEY REPRESENT A pair of gold keys represents your DSS Diffie Hellman key pair The key pair consists of your private key and your public key a A single gold key represents a DSS Diffie Hellman public key Qo A pair of blue keys represents your RSA key pair The key pair consists of your private key and your public key e A single blue key represents an RSA public key On W hen a key or key pair is grayed out they are temporarily unavailable for decrypting and signing You can disable a key from the PG Pkeys window which prevents seldom used keys from cluttering up the Key Selection dialog 60 Chapter 5 Managing Keys And Setting ICONS W HAT THEY REPRESENT A key with a red line through it indicates that the key has been revoked Users
31. to migrate to the new PGP DSS keys as your preferred method for making digital signatures because DSS uses SHA as its secure hash algorithm How to Protect Public Keys from Tampering In a public key cryptosystem you don t have to protect public keys from exposure In fact it s better if they are widely disseminated But it s important to protect public keys from tampering to make sure that a public key really belongs to whom it appears to belong to This may be the most important vulnerability of a public key cryptosystem See Protecting Your Keys in Chapter 3 for procedures Let s first look at a potential disaster then describe how to safely avoid it with PGP PGP for Personal Privacy Version 5 0 User s Guide for W indows 95 96 Suppose you want to send a private message to Alice You download Alice s public key certificate from an electronic bulletin board system BBS You encrypt your letter to Alice with this public key and send it to her through the BBS s e mail facility Unfortunately unbeknownst to you or Alice another user named Charlie has infiltrated the BBS and generated a public key of his own with Alice s user ID attached to it He covertly substitutes his bogus key in place of Alice s real public key You unwittingly use this bogus key belonging to Charlie instead of Alice s public key All looks normal because this bogus key has Alice s user ID Now Charlie can decipher the message intended for Alice because he h
32. usually don t even know their stuff is snake oil They may be good software engineers but they usually haven t even read any of the academic literature in cryptography But they think they can write good cryptographic software And why not After all it seems intuitively easy to do so And their software seems to work okay Anyone who thinks they have devised an unbreakable encryption scheme either is an incredibly rare genius or is naive and inexperienced Unfortunately I sometimes have to deal with would be cryptographers who want to make improvements to PGP by adding encryption algorithms of their own design I remember a conversation with Brian Snow a highly placed senior cryptographer with the NSA He said he would never trust an encryption algorithm designed by someone who had not earned their bones by first spending a lot of time cracking codes That did make a lot of sense I observed that practically no one in the commercial world of cryptography PGP for Personal Privacy Version 5 0 User s Guide for W indows 105 106 qualified under this criterion Yes he said with a self assured smile And that makes our job at NSA so much easier A chilling thought I didn t qualify either The government has peddled snake oil too After World War II the US sold German Enigma ciphering machines to third world governments But they didn t tell them that the Allies cracked the Enigma code during the war a fact that remained class
33. won t even reveal how his proprietary encryption scheme works but assures me it s a brilliant scheme and I should trust it l m sure he believes that his algorithm is brilliant but how can I know that without seeing it In all fairness I must point out that in most cases these terribly weak products do not come from companies that specialize in cryptographic technology Even the really good software packages that use DES in the correct modes of operation still have problems Standard DES uses a 56 bit key which is too small by today s standards and may now be easily broken by exhaustive key searches on special high speed machines The DES has reached the end of its useful life and so has any software package that relies on it There is a company called AccessData 87 East 600 South Orem Utah 84058 phone 1 800 658 5199 that sells a package for 185 that cracks the built in encryption schemes used by WordPerfect Lotus 1 2 3 MS Excel Symphony Quattro Pro Paradox MS Word and PKZIP It doesn t simply guess passwords it does real cryptanalysis Some people buy it when they forget their password for their own files Law enforcement agencies buy it too so they can read files they seize I talked to Eric Thompson the Chapter 6 Security Features and Vulnerabilities author and he said his program only takes a split second to crack them but he put in some delay loops to slow it down so it doesn tlook so easy to the customer
34. 4 4000 From the PGPkeys window you can create new key pairs and manage all of your other keys For instance this is where you examine the attributes associated with a particular key specify how confident you are that the key actually belongs to the alleged owner and indicate how well you trust the owner of the key to vouch for the authenticity of other user s keys For a complete explanation of the key management functions you perform from the PGPkeys window see Chapter 5 Chapter 2 Getting Started Setting Preferences By choosing the PGP Preferences option from the PGP pop up menu you can access the PGP Preferences dialog box where you specify settings which affect how the PGP program functions based on your computing environment PGP Preferences RES General Key Files Email KeyServer Encryption and Signing Preference p es va i IV Cache encryption passphrases for 120 seconds Cache signing passphrasesfor 120 seconds T Warm when encrypting to marginally valid keys Key Generation Preferences M Faster key generation By clicking on the appropriate tab you can advance to the preference settings you want to modify For a complete explanation of these settings see Chapter 5 Getting Help By choosing the Help option from the PGP pop up menu you can access the PGP help system which provides a general overview and instructions for all of the procedures you are likely to p
35. A ty ised aii d4 1 0 44949494004444R0008 22 To create a new key pair ido tpud buie tue doe dob d D acil E 23 Contents pects Chg REYS LP 33 Dismibuting Your Public KEY ius eode Rosen rici n ico ddan ipo eed 35 Making your Public Key Available Through a Key Server cece eee nee 35 To send your public key to a key server nauuna 36 Including your Public Key in an E mail Message cece eee ee 37 To include your public key in an e mail message 1 0 cece eee eee 37 Exporting your Public Key do 3 File 2s ocak ririri cag ERE 4x Sk See ee ES 37 D btaining the Public Keys of Others cn cae caeer eae vege vee ee de 38 Getting Public Keys frm a Key Server oo cece ccc ee eee eens 38 To get someone s public key from a key Server cc eee eee 39 Adding Public Keys from E mail Messages 1 0 cece eee eee eens 39 Imporing s Public Key tons Ale jig ui sex rep EA OE ENERGIE eda 40 Verifying the Authenticity ofa Key sse 40 Chapter 4 Sending and Receiving Private E mail esee 43 Encrypting and Signing E mail 0 cece e 43 Encrypting and Signing with Supported E mail Applications 04 43 To encryptand sign with supported e mail applications lisse 44 Encrypting and Signing Via Wie CliBDORBT iic uasss gow eres wee ow Seed ks 46 To encryptand sign via the clipboard 2 1 eee 46 Encrypting and Signing from the Windows Explorer 0 00 c eu eeae 48 To encr
36. BOSS aousas saec ikri ra PEES rE PORE BEY RERO E dope 86 How Public Key Cryptography Works issssssee enn 86 How Your Files and Messages are Encrypted islslssessssssse 87 The POP Symmetric AGNES au sia opp Rack nkire Cl eod E os 88 lists COMMISION ccespetentbpsxcpeepb poet p EWqupex b Esq 90 About the Random N umbers used as Session Keys 0 0 0 esses 91 Hew Decryption WORKS assacxsacceaxhaseo god hecho QUEE COR IO PRODR AO B xb d 91 How Digital Signatures Work iiu ssec eek x m d e e 92 Aboutthe Message Digest 2c ccc csece eves diese eeee ee ei rei 4 E 94 How to Protect Public Keys from Tampering 000 e eee eee 95 How Does PGP Keep Track of Which Keys are Valid 00000008 99 How to Protect Private Keys from Disclosure 0 0 cee eee 101 W hat If You Lose Your Private Key ccc eee nnn 102 BEWARE OF Snake OW pokes kai ect iced eos dab ERE SRG SE RRO EAS 103 rUD CcHDD s sce reeks Phe eee RAE eRe AEE TERE ES 108 Compromised passphrase and Private Key cee ee 108 Public Key Tampenii ae i asp x wa CE RHEE RS Sh RR RR OR OR EO Ro 109 Wat Due Dekted Files os cccicas eds qe db Ede E RQE S a E REP X Edad we 109 Vapisec and Trojan HOTSES ccc ESSE ESPERE ESPERE S44 DER Re dE 110 Swap Files or Virtual Memory isse m 11 Physical Security Breach a socscs aac eo RO EORR TERRE EERE Rod 112 TempespA TAG ys cet e cc eee deere UR Phe o lo RE Rol do E dde dlc 112 Protecting Against Bogus TimestampS
37. GPkeys window General Preferences You specify general encryption settings from the General pane PGP Preferences 2 xi General Key Files Email KeyServer m Encryption and Signing Preferences Iv ln Iv Cache decryption passphrases for 120 seconds Cache signing passphrases for 120 seconds Show recipients when encrypting to marginally valid keys Key Generation Preferences v Faster key generation Cancel Help Always Encrypt to Default Key When this setting is selected all the e mail messages or file attachments you encrypt with a recipient s public key are also encrypted to you using your default public Chapter 5 Managing Keys And Setting key It is useful to leave this setting turned on so that you have the option of decrypting the contents of any e mail or files you have previously encrypted Cache Decryption Passphrase for Seconds This setting specifies the amount of time in seconds that your encryption passphrase is stored in your com puter s memory If you regularly compose or read sev eral e mail messages in succession you may want to increase the amount of time your passphrase is cached so you don t have to enter your passphrase over and over again to get through all of your mail However you should be aware that the longer your passphrase is stored in your computers memory the more time a sophisticated snooper has to get hold of this h
38. I have risked my freedom I m not about to allow a product with my name on it to have any secret back doors PGP for Personal Privacy Version 5 0 User s Guide for W indows 107 108 Vulnerabilities No data security system is impenetrable PGP can be circumvented in a variety of ways In any data security system you have to ask yourself if the information you are trying to protect is more valuable to your attacker than the cost of the attack This should lead you to protecting yourself from the cheapest attacks while not worrying about the more expensive attacks Some of the discussion that follows may seem unduly paranoid but such an attitude is appropriate for a reasonable discussion of vulnerability issues f all the personal computers in the world 260 million were put to work on a single PGP encrypted message it would still take an estimated 12 million times the age of the universe on average to break a single message William Crowell Deputy Director National Security Agency March 20 1997 Compromised passphrase and Private Key Probably the simplest attack is if you leave your passphrase for your private key written down somewhere If someone gets it and also gets your private key file they can read your messages and make signatures in your name Here are some recommendations for protecting your passphrase Don tuse obvious passphrases that can be easily guessed such as the names of your kids or spouse 2
39. ING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE EVEN IF PRETTY GOOD PRIVACY INC HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES BECAUSE SOME STATES DO NOTALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES THE ABOVE LIMITATION MAY NOT APPLY TO YOU This book was written by Mike lannamico special thanks to Gail Kesner Haspert Contents Table of Contents Table of Contents iiiuuaananaaaXaaARRRRRRRERRRRRRAdaGRRaRdR da V Chapter 1 Introducing PGP for Personal Privacy enne 1 Ce Coa ai eee eee eee RARE eo ee E EHE RERO I SUR deos uu Usus xia e ts 2 Create a Private and Public Key Pair liliis 3 Exchange Public Keys with QUES issssass se sek or e eos nee eee erae 3 Cerny and Validate Your KEYS acecsecsececnerhbereterb4br hau pergeeckenr i 3 Ertrypt and Sign Peu EMA iussu sang ira ac ana dd ER d d Uo e wo s pn EOS 4 D cryptatid Venty Tour EMAI ccc de cdeck dackeg o op ae eee p OG Y ore bos 4 About THIS Manual 4e desi eek REPE cunts EE ER wid eR Edo Td es 5 Chapter 1 Introducing PGP for Personal Privacy 000s cece cece eee 8 Chapter 2 Gand SITIBU cu aig ka d LEATHER ARAE ERU RESO ED ESRAS 5 Chapter 3 Making and Exchanging Keys cascar isis esee 5 Chapter 4 Sending and Receiving Private E mail sss 5 Chapter 5 Managing Keys And Setting Preferences liii sisse 5 Chapter 6 Security Features and Vulnerabilities isses 5 PGP for Personal Privacy Ve
40. One good way to check a fingerprint is to have the owner read their fingerprint over the phone so that you can compare it with the fingerprint shown for your copy of their public key You can also check the authenticity of someone s key by comparing the fingerprint on your copy of their public key to the one listed on a public key server since it is assumed that the owner periodically checks to make sure that it remains valid Enabled Indicates whether the key is currently enabled or not When a Key is disabled it is dimmed in the PGPkeys window and is not available for performing any PGP functions However the key remains on your keyring and you can enable it again if it becomes necessary To enable or disable a key select or clear the Enabled check box or choose Enable or Disable from the Keys menu This feature is useful for preventing keys that you don t use on a regular basis from cluttering up the recipients dialog when you are sending encrypted e mail Change Passphrase Changes the passphrase for a private key If you ever decide that your passphrase is no longer a secret per haps you caught someone looking over your shoulder click this button to enter a new passphrase Specifying a Default Key Pair When you sign a message or someone s public key your default key set is used If you have more than one set of keys you may want to specifically designate one pair as your default set The current default key set is displayed
41. Pretty Good Privacy PGP for Personal Privacy Version 5 0 For Windows 95 W indows NT User s Guide PGP Inc 1997 by Pretty Good Privacy Inc All rights reserved 5 97 Printed in the United States of America PG P for Personal Privacy Version 5 0 Record the serial number from your License Agreement in the space provided below Copyright 1990 1997 by Pretty Good Privacy Inc All Rights Reserved PG P Pretty G ood and Pretty Good Privacy are registered trademarks of Pretty G ood Privacy Inc All other trademarks and registered trademarks are the property of their respective owners Pretty Good Privacy Inc may have patents and or pending patent applications covering subject matter in this document The furnishing of this document or the software does not give you any license to these patents PG P uses public key algorithms described in U S Patentnumbers 4 200 770 4 218 582 4 405 829 and 4 424 414 licensed exclusively by Public Key Partners PG P uses the IDEA cryptographic cipher described in U S Patent number 5 214 703 and is licensed from Ascom Tech AG IDEA is a trademark of Ascom Tech AG The compression code in PGP is by Mark Adler and Jean loup Gailly taken with permission from the free Info ZIP implementation The software provided with this documentation is licensed to you for your individual use under the terms of the End User License Agreement and Limited W arranty provided with the sof
42. Privacy Version 5 0 User s Guide for W indows 49 If you have elected to sign the files you will be asked to supply your passphrase If you are adding your signature to the encrypted file and would like the signature stored in a separate file select the Separate Signature File check box If you want the output of the encrytped file saved in a text format that can be handled by all e mail applications select the Text Out checkbox You should note that selecting this option increases the size of the file by about 30 percent Select the public keys by dragging them to the recipients list and then click OK The Save Encrypted File As dialog box appears Save Encrypted File As 2 x Save in fa Photolmpact Screen Capture z d E fio Save as type PGP Files asc pgp Cancel Specify the location and enter the name of the file where you want to save the encrypted version of the file The pgp extension is automatically appended to the file name unless you have turned on the ASCII Armor option in which case the asc extension is used Click Save to save the file to the specified location If you look in the directory where you saved the file you will find a file with the specified name represented by one of two icons pgp asc encrypted with standard output encrypted with text output Chapter 4 Sending and Receiving Private E mail Decrypting and Verifying E mail The quickest and
43. RR RRRRER E RE RR a 66 To sign someone s PURINE KEY ok ee pee iut ge eee gs EE RE RE ES d 66 Granting Trust for Key Validations 0 cee 67 To granttrustfora key T eee TUTUP bp pxxaaex OF Disabling and Enabling KES assise ea coeds eee oro ei ox OE AGIR RO 68 pHDIDISOD AES PUTET 68 To enable a key gd ds ore dike di io ds TE 69 Deleting a Key or Signature ssi he aces bee eee Re eR be RE Ree d 69 To delete a key signatureoruser ID se ees 69 Changing your Passphrds amp siue uuuu ue mm ee ROBA CAR ee d 69 To change yout passphrase iia ceeadcekxkexr Rakion na eee senese 09 mporing and Exporting KEYS cc 0icoe kie ae b reeda a aa 1 To mpate kar TERI DEO osea dose Rev QR a d ecd Gee me e ad 71 To exporta key to a file gadis TET TEET siid eu dd Revoling a KEY cases exe ue desided eee ebe ibiti des ERR RENE TS SER 12 TO PERO SU esca oos dido aoa 9 V Edo oh deb o EE ODE 72 HRS Your Pee el TUUS aisadodadadaiedd sos eus eens cupa Robo RR 74 General PEIPER BS Loupe request din ped Oo att eue todd epee wad Bde 74 viii Contents Key Files Preferences 00 0 0 cc ee ee Rm hh RR mE RUE RR Rh a 76 Email Preference ss ci ecco eee Oe ee S ROME REREAD OE dor RR Ee o at Key Server Prenerenees oacocsepnhreerrpbEPARRP DEERIM URae d EE REET ELS 79 Chapter 6 Security Features and Vulnerabilities leere 81 Wiig woe POP ou ccoaada snb eee RR RUE ARR Rue aM ER ERROR Rr a 81 Encryphoh
44. Receiving Private E mail 3 Choose Decrypt Verify from the PGP submenu of the File menu or press the right mouse button to open the pop up menu and then choose Decrypt Verify Open Quick View Add to Zip Send To gt New Create Shortcut Delete Rename Properties Close The passphrase dialog box appears requesting that you enter your passphrase PGP Enter Passphrase 2 x Enter passphrase for your private key IV Hide Typing 4 Enter your passphrase and then click OK PGP for Personal Privacy Version 5 0 User s Guide for Windows 55 If the file has been signed a message appears indicating whether the signature is valid Signature Result Good signature from Michael J lannamico lt mji pap com gt Signature made on Wed May 21 15 15 11 1897 5 Click OK The Save Encrypted File As dialog box appears Save Encrypted File As i2 1x Savein MSOffice q ol ek zz E File name MSCREATE DIF pop Save as type aan Files asc pgp x Cancel 6 Specify the location and enter the name of the file where you want to save the decrypted version of the file If you do not explicitly enter a name the original name is used 7 Click the Save button to save the file The decrypted file is saved in the specified location If there are any signatures an attempt is made to verify the signature and a message appears indicating whether the signature is valid 56 Chapter 4 Se
45. This setting specifies the column number where a hard carriage return is used to wrap the text in your digital signature to the next line This feature is necessary because all applications do not handle word wrapping in the same way which could cause the lines in you dig itally signed messages to be broken up in a way that cannot be read properly By default this setting is set to 78 which prevents problems with most applications Encrypt New Messages by Default Leaves the Encryption function turned on for your e mail application The lock icon will remain indented to indicate that the encryption function is turned on Sign New Messages by Default Leaves the Signature function turned on for your e mail application The quill icon will remain indented to indi cate that the signatory function is turned on Chapter 5 Managing KeysAnd Setting Key Server Preferences Click the Key Server tab to advance to the pane where you specify settings for the key server you are using Server Port PGP Preferences 24 x General Key Files Email KeyServer Server kers pap com Port for Automatically Retrieve Unknown Keys Reset Cancel Help Specifies the address for the public key server that is used by PGP to send and retrieve public keys You should not change this unless you have a different loca tion The port address for the public key server Automatically Retrieve Unknown Keys Reset W
46. Use spaces and a combination of numbers and letters in your pass phrase If you make your passphrase a single word it can be easily guessed by having a computer try all the words in the dictionary until it finds your password That s why a passphrase is so much better than a password A more sophisticated attacker may have his com puter scan a book of famous quotations to find your passphrase 3 Be creative Use an easy to remember but hard to guess passphrase you can easily construct one by using some creatively nonsensical sayings or very obscure literary quotes Chapter 6 Security Features and Vulnerabilities Public Key Tampering A major vulnerability exists if public keys are tampered with This may be the most crucially important vulnerability of a public key cryptosystem in part because most novices don t immediately recognize it The importance of this vulnerability and appropriate hygienic countermeasures are detailed in the section How to Protect Public Keys from Tampering earlier in this chapter To summarize When you use someone s public key make certain it has not been tampered with A new public key from someone else should be trusted only if you got it directly from its owner or if it has been signed by someone you trust Make sure no one else can tamper with your own public keyring Maintain physical control of both your public keyring and your private key preferably on your own personal computer rather than on a r
47. ard for NSA to design an encryption algorithm that only they can crack if no one else can review the algorithm And now with the Clipper chip the NSA is pushing SKIPJACK another classified cipher they designed Are they deliberately selling snake oil There are three main factors that have undermined the quality of commercial cryptographic software in the US The first is the virtually universal lack of competence of implementors of commercial encryption software although this is starting to change since the publication of PGP Every software engineer fancies himself a cryptographer which has led to the proliferation of really bad crypto software Chapter 6 Security Features and Vulnerabilities The second is the NSA deliberately and systematically suppressing all the good commercial encryption technology by legal intimidation and economic pressure Part of this pressure is brought to bear by stringent export controls on encryption software which by the economics of software marketing has the net effect of suppressing domestic encryption software The other principle method of suppression comes from the granting all the software patents for all the public key encryption algorithms to a single company affording a single choke point to suppress the spread of this technology although this crypto patent cartel broke up in the fall of 1995 The net effect of all this is that before PGP was published there was almost no highly
48. as the matching private key He may even re encrypt the deciphered message with Alice s real public key and send it on to her so that no one suspects any wrongdoing Furthermore he can even make apparently good signatures from Alice with this private key because everyone will use the bogus public key to check Alice s signatures The only way to prevent this disaster is to prevent anyone from tampering with public keys If you got Alice s public key directly from Alice this is no problem But that may be difficult if Alice is a thousand miles away or is currently unreachable Perhaps you could get Alice s public key from a mutually trusted friend David who knows he has a good copy of Alice s public key David could sign Alice s public key vouching for the integrity of Alice s public key David would create this signature with his own private key This would create a signed public key certificate and would show that Alice s key had not been tampered with This requires that you have a known good copy of David s public key to check his signature Perhaps David could provide Alice with a signed copy of your public key also David is thus serving as an Introducer between you and Alice This signed public key certificate for Alice could be uploaded by David or Alice to the BBS and you could download it later You could then check the signature via David s public key and thus be assured that this is really Alice s public key No impostor can foo
49. assage of time Sadly the biggest obstacle to PGP for Personal Privacy Version 5 0 User s Guide for W indows 89 90 IDEA s acceptance as a standard has been the fact that Ascom Systec holds a patent on its design and unlike DES and CAST IDEA has not been made available to everyone on a royalty free basis As a hedge PGP includes three key triple DES in its repertoire of available block ciphers The DES was developed by IBM in the mid 1970s While it has a good design its 56 bit key size is too small by today s standards Triple DES is very strong and has been well studied for many years so it might be a safer bet than the newer ciphers such as CAST and IDEA Triple DES is the DES applied three times to the same block of data using three different keys except that the second DES operation is run backwards in decrypt mode Although triple DES is much slower than either CAST or IDEA speed is usually not critical for e mail applications While triple DES uses a key size of 168 bits it appears to have an effective key strength of at least 112 bits against an attacker with impossibly immense data storage capacity to use in the attack According to a paper presented by Michael Weiner at Crypto96 any remotely plausible amount of data storage available to the attacker would enable an attack that would require about as much work as breaking a 129 bit key Triple DES is not encumbered by any patents PGP public keys that were generated by PGP
50. at is compatible with older versions of the program PGP for Personal Privacy Version 5 0 User s Guide for W indows 25 26 If you plan to correspond with individuals who have the latest version of PGP you can take advantage of the new technology and generate a pair of DSS Diffie Hellman keys If you want to be able to exchange e mail with all PGP users you should make a pair of RSA keys and a pair of DSS Diffie Hellman keys and then use the appropriate pair depending on the version of PGP used by the recipient with whom you are communicating Click Next to advance to the next dialog box The Key Generation Wizard asks you to specify a size for your new keys Key Generation Wizard How large a key pair do you wish to generate As a rule larger keys are more secure but slower For most applications 1024 2048 bit keys are quite sufficient Key Pair Size 768 bits 1024 bits C 1536 bits 1024 DSA 1536 c amal 3072 bits 2048 DSA 3072 ElGamal C Custom 512 4096 bits k 7 i Dn lt Back Cancel Help Select a key size from 768 to 3072 or enter any key size from from 512 to 4096 Note that RSA keys are limited to 2048 bits in order to maintain compatibility with older versions of PGP The key size corresponds to the number of bits used to construct your digital key The larger the key the less chance that someone will ever be able to crack it but the longer it will
51. ation process Encrypt Clipboard Sign Clipboard Encrypt And Sign Clipboard Decrypt Verify Clipboard Add Key from Clipboard Edit Clipboard Text Launch Associated Viewer Launch PGPkeys PGP Preferences Help Quit PGPmail PGP for Personal Privacy Version 5 0 User s Guide for W indows 53 54 The PGP Enter Passphrase dialog box appears requesting that you enter your passphrase PGP Enter Passphrase i2 x Passphrase of selected key v Hide Typing u Cancel Enter your passphrase and then click OK The message is decrypted If there are any signatures an attempt is made to verify the signature and a message appears indicating whether the signature is valid To view the contents of the deciphered e mail message choose Edit Clipboard Text or Launch Associated Viewer from the PGP pop up menu You can then copy the contents back to your text editor and save it if you like Decrypting and Verifying from the Windows Explorer If the e mail you receive has file attachments and you are not using a PGP MIME compliant e mail application you must decrypt them from the Windows Explorer To decrypt and verify from the Windows Explorer 1 2 Open the Windows Explorer from the Start menu Select the file or files that you want to decrypt and verify You can select multiple files but you must go through the process of decrypting and verifying each individual file Chapter 4 Sending and
52. atures and Vulnerabilities Committee that public availability of strong cryptography must be curtailed by the government although no one had suggested that cryptography was used by the bombers The Electronic Privacy Information Center EPIC obtained some revealing documents under the Freedom of Information Act In a briefing document titled Encryption The Threat Applications and Potential Solutions and sent to the National Security Council in February 1993 the FBI NSA and Department of Justice DOJ concluded that Technical solutions such as they are will only work if they are incorporated into all encryption products To ensure that this occurs legislation mandating the use of Government approved encryption products or adherence to Government encryption criteria is required The government has a track record that does not inspire confidence that they will never abuse our civil liberties The FBI s COINTELPRO program targeted groups that opposed government policies They spied on the anti war movement and the civil rights movement They wiretapped the phone of Martin Luther King Jr Nixon had his enemies list And then there was the Watergate mess Congress now seems intent on passing laws curtailing our civil liberties on the Internet At no time in the past century has public distrust of the government been so broadly distributed across the political spectrum as it is today If we want to resist this unsettling trend in t
53. blic Keys from E mail Messages One convenient way to get a copy of someone s public key is to have them include it when they send you encrypted e mail If you have an e mail applications that is supported by the PGP plug in then adding the senders public key to your public key ring can be accomplished by simply clicking a button For example when a mail message arrives with a block of text containing someone s public key click the key and envelope button to have the key stored on your public keyring PGP for Personal Privacy Version 5 0 User s Guide for W indows 39 40 If you are using an e mail application that is not supported by the plug ins you can copy the block of text that represents the public key and paste it into the PGPkeys window and thus add the key to your public keyring Importing a Public Key from a File Another method of obtaining someone s public key is to have them save it to a file from which you can import it or copy and paste it into your public keyring There are several methods of extracting someone s public key and adding it to your public keyring Choose Import from the Keys menu and then enter the name of the file where the public key is stored Drag the file containing the public key from the Windows Explorer window onto the PGPkeys window Open the text document where the public key is stored select the block of text representing the key then choose Copy from the Edit menu Then go to the PGP
54. both linear and differential cryptanalysis the two most powerful forms of cryptanalysis in the published literature both of which have been effective in cracking DES While CAST is too new to have developed a long track record its formal design and the good reputations of its designers will undoubtedly attract the attentions and attempted cryptanalytic attacks of the rest of the academic cryptographic community I m getting nearly the same preliminary gut feeling of confidence from CAST that I got years ago from IDEA the cipher I selected for use in earlier versions of PGP At that time IDEA was also too new to have a track record but it has held up well The IDEA International Data Encryption Algorithm block cipher is based on the design concept of mixing operations from different algebraic groups It was developed at ETH in Zurich by James L Massey and Xuejia Lai and published in 1990 Early published papers on the algorithm called it IPES Improved Proposed Encryption Standard but they later changed the name to IDEA So far IDEA has resisted attack much better than other ciphers such as FEAL REDOC II LOKI Snefru and Khafre And IDEA is more resistant than DES to Biham and Shamir s highly successful differential cryptanalysis attack as well as attacks from linear cryptanalysis As this cipher continues to attract attack efforts from the most formidable quarters of the cryptanalytic world confidence in IDEA is growing with the p
55. brain If you feel you must write down your passphrase keep it well protected perhaps even more well protected than the private key file And keep backup copies of your private key remember you have the only copy of your private key and losing it will render useless all the copies of your public key that you have spread throughout the world The decentralized non institutional approach PGP supports for management of public keys has its benefits but unfortunately this also means we can t rely on a single centralized list of which keys have been compromised This makes it a bit harder to contain the damage of a private key compromise You just have to spread the word and hope everyone hears about it If the worst case happens your private key and passphrase are both compromised hopefully you will find this out somehow you will have to issue a key compromise certificate This kind of certificate is used to warn other people to stop using your public key You can use PGP to create such a certificate by using the Revoke command from the PGPkeys menu Then you must somehow send this compromise certificate to everyone else on the planet or at least to all your friends and their friends et cetera Their own PGP software will install this key compromise certificate on their public keyrings and will automatically prevent them from accidentally using your public key ever again You can then generate a new private public key pair and publish t
56. ce to the next field 70 Chapter 5 Managing KeysAnd Setting 5 Enter your new passphrase in the center field and then press the Tab key to advance to the bottom field 6 Confirm your entry by entering your new passphrase again 7 Click OK Importing and Exporting Keys Although you often distribute your public key and obtain the public keys of others by cutting and pasting the raw text from a public key server you can also exchange keys by importing and exporting them as separate text files For instance someone could hand you a disk containing their public key or you might want to make your public key available over an FIP server To import a key from a file l Select the key you want to import from a file 2 Choose Import from the Keys menu The Select File Containing Key dialog box appears Select File Containing Key Look in PGPmail t AddedKey t t Albert P David txt is license txt Papcorp asc pubkey txt Al Readme tst mme Files of type Text Files txt asc Cancel 3 Select the file that contains the key you want to import and then click Open The imported key appears in the PGPkeys window where you can use it to encrypt data and verify someone s digital signature PGP for Personal Privacy Version 5 0 User s Guide for W indows 71 72 To export a key to a file l Select the key you want to export to a file 2 Choose Export from the Key
57. ch you access by pressing the right mouse button Open Add to Zip Send To gt Encrypt Sign New gt Create Shortcut Delete Rename Properties Close The Key Selection Dialog box appears where you can select the recipient s public keys for the file you are encrypting or signing S PGP Key Selection Dialog 2 x Drag usere fom is ito the Recbions let Vaid Tut Sue d a amp Brett A Thomas cem com pz 1024 amp Brett A Thomas lt quark baz com gt Es pc 1024 amp Carolyn Turbyfill lt turby pap com gt See oss 1024 2048 amp Damon Gallaty lt dgal pap com gt Ei pz 1024 Damon J Gallaty lt dgal cad gatech edu gt En Gy 1024 amp Jason Bobier lt jason pgp com gt EI Gx 2048 amp Jason Bobier lt jbobier prismatix com gt En pu 2048 amp Jason Bobier lt jbobier privnet com gt pm p 2048 Jason Bobier lt k059509 hobbes kz00 edu gt Emu pu 2048 amp Philip Nathan philipn amp ipgp com pm p 1024 amp Philip R Zimmermann lt prz acm org Ei pu 1024 xi 2048 S Michael J lannamico lt mii pgp com gt ptions Text Output Cancel Help When sending files as attachments with some e mail applications you may need to check the Text Output check box to have the file saved as ASCII text This is sometimes necessary in order to send a binary file using older e mail applications PGP for Personal
58. cipher that uses the same key to both encrypt and decrypt The three symmetric block ciphers offered by PGP are CAST Triple DES and IDEA They are not home grown algorithms They were all developed by teams of cryptographers with distinguished reputations Chapter 6 Security Features and Vulnerabilities For the cryptographically curious all three ciphers operate on 64 bit blocks of plaintext and ciphertext CAST and IDEA have key sizes of 128 bits while triple DES uses a 168 bit key Like Data Encryption Standard DES any of these ciphers can be used in cipher feedback CFB and cipher block chaining CBC modes PGP uses them in 64 bit CFB mode I included the CAST encryption algorithm in PGP because it shows promise as a good block cipher with a 128 bit key size it s very fast and it s free Its name is derived from the initials of its designers Carlisle Adams and Stafford Tavares of Northern Telecom Nortel Nortel has applied for a patent for CAST but they have made a commitment in writing to make CAST available to anyone on a royalty free basis CAST appears to exceptionally well designed by people with good reputations in the field The design is based on a very formal approach with a number of formally provable assertions that give good reasons to believe that it probably requires key exhaustion to break its 128 bit key CAST has no weak or semiweak keys There are strong arguments that CAST is completely immune to
59. crypted Because the public key encryption algorithm is much slower than conventional single key encryption encryption is better accomplished by using the process shown in Figure 3 PGP for Personal Privacy Version 5 0 User s Guide for W indows 87 88 Figure 3 Recipient s Public Key 010101 1001001001 Random Number for Session Key 0100000101000011 0100000101000011 Encrypted Session Key Encryption Using Public K ublic Key Encryption Plaintext Encryption Using Encrypted Message Secret Key Message Encryption Using PGPmail sender employs Conventional and Public Key Encryption to encrypt the file or message in a single operation A high quality fast conventional secret key encryption algorithm is used to encipher the message This original unenciphered message is called plaintext In a process invisible to the user a temporary random key created just for this one session is used to conventionally encipher the plaintext file Then the recipient s public key is used to encipher this temporary random conventional key This public key enciphered conventional session key is sent along with the enciphered text called ciphertext to the recipient The PGP Symmetric Algorithms PGP offers a selection of different secret key algorithms to encrypt the actual message By secret key algorithm we mean a conventional or symmetric block
60. d of course a compromise of your own private key could expose all messages sent to you To protect your private key you can start by always keeping physical control of your private key Keeping it on your personal computer at home is OK or keep it in your notebook computer that you can carry with you If you must use an office computer that you don t always have physical control of then keep your public and private keyrings on a write protected removable floppy disk and don t leave it behind when you leave the office It wouldn t be a good idea to allow your private key to reside on a remote timesharing computer such as a remote dial in UNIX system Someone could eavesdrop on your modem line and capture your passphrase and then obtain your actual private key from the remote system You should only use your private key on a machine that is under your physical control See Chapter 5 for additional information Don t store your passphrase anywhere on the computer that has your private key file Storing both the private key and the passphrase on the same computer is as dangerous as keeping your PIN in the same wallet as your Automatic Teller Machine bank card You don t want somebody to get their hands on your disk containing both the passphrase and the PGP for Personal Privacy Version 5 0 User s Guide for W indows 101 102 private key file It would be most secure if you just memorize your passphrase and don t store it anywhere but your
61. d with the key You may also want to sign someone s public key to indicate that you believe it is valid assign a level of trust to the key s owner or change a passphrase for your private key You perform all of these key management functions from the PGPkeys window The PGPkeys Window To open the PGPkeys window click the lock and key icon in the System tray then choose Launch PGPkeys 41 79 21 300 PM In the PGPKeys window you see the keys you have created for yourself as well as any public keys you have added to your public keyring 2i PGPkeys ioj x File Edit Keys Help Keys vaid Trust Crean Size Brett A Thomas lt bat pgp com gt 5 18 97 1024 2048 E Qe Carolyn Turbyfill lt turby pap com gt 4 8 97 1024 2048 E Damon Gallaty lt dgal pagp com gt Eu ums 5 20 97 1024 3072 Dave Heller lt dheller pgp com gt es Gey 5 20 97 1024 2048 Qe DJ Young DSS lt di pagp com gt aes Gey 5 16 97 1024 2048 E Qe Lloyd L Chambers lt lloyd pgp com gt C eee 5 20 97 1024 4096 8 Mark J McArdle lt markm pgp com gt LEES eee 5 15 97 1024 2048 Qz Michael lannamico lt mji pgp com gt Lr E sn 3 37 1024 4021 eae Michael J lannamico lt mji pap com gt Michael J lannamico lt mji pap com gt Coo i Philip R Zimmermann lt prz acm 2 21 97 Sh Michael J lannamico lt mji pagp 4 7 97 Qe PGP Support Key DSS pgpsupport p
62. decentralized environment where individuals exchange personal keys This whole business of protecting public keys from tampering is the single most difficult problem in practical public key applications It is the Achilles heel of public key cryptography and a lot of software complexity is tied up in solving this one problem You should use a public key only after you are sure that it is a good public key that has not been tampered with and that it actually belongs to the person with whom it purports to be associated You can be sure of this if you got this public key certificate directly from its owner or if it bears the signature of someone else that you trust from whom you already have a good public key Also the user ID should have the full name of the key s owner not just her first name No matter how tempted you are you should never give in to expediency and trust a public key you downloaded from a bulletin board unless it is signed by someone you trust That uncertified public key could have been tampered with by anyone maybe even by the system administrator of the bulletin board If you are asked to sign someone else s public key certificate make certain that it really belongs to that person named in the user ID of that public key certificate This is because your signature on her public key certificate is a promise by you that this public key really belongs to her Other people who trust you will accept her public key becau
63. digital signature and authenticity 41 deleting 69 overview 2 verifying 2 digital signatures 92 disabling keys 68 disclosure 101 PGP for Personal Privacy Version 5 0 User s Guide for W indows 121 disk system requirements 7 distributing your public keys 35 DSS Diffie Hellman technology keys 8 creating 25 email adding a new user name 64 checking signature 2 copying public keys from 39 decrypting 4 51 from W indows Explorer 54 56 via the Clipboard 53 within Eudora 51 52 encrypting 4 43 from W indows Explorer 48 50 via the Clipboard 46 48 with Eudora 43 46 message including your public key in 37 private receiving 2 43 sending 2 43 setting preferences 77 signing 2 4 43 from W indows Explorer 48 50 via the Clipboard 46 48 with Eudora 43 46 verifying 4 51 from W indows Explorer 54 56 via the Clipboard 53 within Eudora 51 52 Enabled property 63 enabling keys 68 encrypting email 4 43 overview 2 from the Clipboard 13 from W indows Explorer 48 50 using Eudora 43 46 122 via the Clipboard 46 48 within Eudora 51 52 encryption digital signature technology 8 DSS Diffie Hellman technology 8 how it works 21 setting preferences 74 exchanging public keys 3 obtaining others 38 40 expiration setting for key pairs 27 Expire property 62 exporting keys to files 72 public keys to files 37 F file attachments 54 files exporting keys to 72 exporting publ
64. disable a key The ability to disable keys is useful when you want to retain a public key for future use but you don t want it cluttering up your recipient list every time you send mail To disable a key l Select the key you want to disable 2 Choose Disable from the Keys menu The key is dimmed and is temporarily unavailable for use Chapter 5 Managing KeysAnd Setting To enable a key l Select the key you want to enable 2 Choose Enable from the Keys menu The key becomes visible and can be used as before Deleting a Key or Signature At some point you may want to remove a key a signature or a user ID associated with a particular key To delete a key signature or user ID l Select the key signature or user ID you want to delete 2 Choose Delete from the Edit menu Changing your Passphrase It is a good idea to periodically change your passphrase If you want to change your passphrase you can easily do so To change your passphrase l Select the key pair for which you want to change the passphrase 2 Choose Key Properties from the Keys menu PGP for Personal Privacy Version 5 0 User s Guide for W indows 69 The Properties dialog box appears Michael J lannamico lt mji pgp com gt v Enabled 3 Click Change Passphrase The Change Passphrase dialog box appears PGP Change Passphrase 4 Enter your old passphrase in the top field and then press the Tab key to advan
65. e first line and your e mail address on the second line It s not absolutely necessary to enter your real name or even your e mail address However using your real name makes it easier for others to identify you as the owner of your public key Also by using your correct e mail address you and others can take advantage of one of a plug in feature that automatically looks up the appropriate key on your current keyring when you address mail to a particular recipient 5 Click Next to advance to the next dialog box The Key Generation Wizard then asks you to choose a key type Key Generation Wizard What type of key would you like to generate If you don t know it s recommended that you generate a DSS Diffie Hellman key pair RSA is the old style PGP key Most new users of PGP will be expecting a DSS Diffie Hellman key x Gi E If you d like more information on the differences between the two key types press the Help button below Y Key Pair Type WE a An af 4 UT taa ee 6 Select a key type either DSS Diffie Hellman or RSA Barlier versions of PGP use an older technology referred to as RSA to generate keys Beginning with this version of PGP you have the option of creating a new type of key based on the newer DSS Diffie Hellman technology If you plan to correspond with individuals who are still using the older RSA keys you will probably want to generate an RSA key pair th
66. e replacement algorithm This means pages that have not been accessed for the longest period of time are the first ones to be swapped to the disk This approach suggest that in most cases the risk is fairly low that sensitive data will be swapped out to disk because PGP doesn t leave it in memory for very long But we don t make any guarantees This swap file may be accessed by anyone who can get physical access to your computer If you are concerned about this problem you may be able to solve it by obtaining special software that overwrites your swap file Another possible cure is to turn off your operating system s virtual PGP for Personal Privacy Version 5 0 User s Guide for W indows 111 112 memory feature Microsoft Windows allows for this and so does the Mac OS Turning off virtual memory means you might need to have more physical RAM chips installed in order to fit everything in RAM Physical Security Breach A physical security breach may allow someone to physically acquire your plaintext files or printed messages A determined opponent might accomplish this through burglary trash picking unreasonable search and seizure or bribery blackmail or infiltration of your staff Some of these attacks may be especially feasible against grassroots political organizations that depend on a largely volunteer staff Don t be lulled into a false sense of security just because you have a cryptographic tool Cryptographic techniques protec
67. e sent through a modem or e mail system If you use PGP and follow reasonable precautions the attacker will have to expend far more effort and expense to violate your privacy If you protect yourself against the simplest attacks and you feel confident that your privacy is not going to be violated by a determined and highly resourceful attacker then you ll probably be safe using PGP PGP gives you Pretty Good Privacy Recommended Introductory Readings Bacard Andre Computer Privacy Handbook Peachpit Press 1995 Garfinkel Simson Pretty Good Privacy O Reilly amp Associates 1995 Schneier Bruce Applied Cryptography Protocols Algorithms and Source Code in C Second Edition John Wiley amp Sons 1996 Schneier Bruce E mail Security John Wiley amp Sons 1995 Stallings William Protect Your Privacy Prentice Hall 1994 PGP for Personal Privacy Version 5 0 User s Guide for W indows 115 116 Other Readings Lai Xuejia On the Design and Security of Block Ciphers Institute for Signal and Information Processing ETH Zentrum Zurich Switzerland 1992 Lai Xuejia Massey James L Murphy Sean Markov Ciphers and Differential Cryptanalysis Advances in Cryptology EUROCRYPT 91 Rivest Ronald The MD5 Message Digest Algorithm MIT Laboratory for Computer Science 1991 Wallich Paul Electronic Envelopes Scientific American Feb 1993 page 30 Zimmermann Philip A Proposed Standard Format for RSA Crypt
68. e through a public key server include it in an e mail message or export or copy it to a file The recipient can then use whatever method is most convenient to add your public key to their public keyring Making your Public Key Available Through a Key Server Probably the best long term and hassle free method for making your public key available is to place it on a public key server where anyone can access it By storing your public key on a key server people can send you e mail without having to explicitly request a copy of your key It also relieves you and others from having to maintain a large number of public keys that you rarely use There are a number of key servers such as those offered by PGP Inc where you can make your public key available for anyone to access It doesn t really matter which key server you use to initially submit your public key because once you submit your key to one server it is automatically propagated to all the other major servers in the world Each site provides a slightly different interface for submitting a public key but the procedure basically requires you to copy the text content of your key and then paste it into the proper place on the key server However when using PGP you can post your public key to a public key server automatically whenever you create a new key or at any time thereafter from within the PGP keys window PGP for Personal Privacy Version 5 0 User s Guide for W indows To send yo
69. ecial trap doors in their products so that the government can read anyone s encrypted messages It reads It is the sense of Congress that providers of electronic communications services and manufacturers of electronic communications service equipment shall ensure that Chapter 6 Security Features and Vulnerabilities communications systems permit the government to obtain the plain text contents of voice data and other communications when appropriately authorized by law It was this bill that led me to publish PGP electronically for free that year shortly before the measure was defeated after rigorous protest from civil libertarians and industry groups The 1994 Digital Telephony bill mandated that phone companies install remote wiretapping ports into their central office digital switches creating a new technology infrastructure for point and click wiretapping so that federal agents no longer have to go out and attach alligator clips to phone lines Now they ll be able to sit in their headquarters in Washington and listen in on your phone calls Of course the law still requires a court order for a wiretap But while technology infrastructures can persist for generations laws and policies can change overnight Once a communications infrastructure optimized for surveillance becomes entrenched a shift in political conditions may lead to abuse of this new found power Political conditions may shift with the election of a new governmen
70. ecrypt and verify e mail messages and files Keys come in key pairs and are stored on keyrings PGP for Personal Privacy Version 5 0 User s Guide for W indows 117 118 Key Escrow A practice where a user of a public key encryption system surrenders their private key to a third party thus permitting them to monitor encrypted communications Key Fingerprint A uniquely identifying string of numbers and characters used to authenticate public keys For example you can telephone the owner of a public key and have him or her read the fingerprint associated with their key so you can compare it with the fingerprint on your copy of their public key to see if they match If the fingerprint does not match then you know you have a bogus key Key ID A legible code that uniquely identifies a key pair Two key pairs may have the same User ID but they will have different Key IDs Key Pair A public key and its complimentary private key In public key cryptosystems like the PGP program each user has at least one key pair Keyring A set of keys Each user has two types of keyrings a private keyring and a public keyring Message Digest A compact distillate of your message or file checksum It represents your message such that if the message were altered in any way a different message digest would be computed from it Passphrase A series of keystrokes that allow exclusive access to your private key which you use to sign and decrypt e mail m
71. em s clock and generating his own public key certificates and signatures that appear to have been created at a different time He can make it appear that he signed something earlier or later than he actually did or that his public private key pair was created earlier or later This may have some legal or financial benefit to him for example by creating some kind of loophole that might allow him to repudiate a signature I think this problem of falsified timestamps in digital signatures is no worse than it is already in handwritten signatures Anyone may write a date next to their handwritten signature on a contract with any date they choose yet no one seems to be alarmed over this state of affairs In some cases an incorrect date on a handwritten signature might not be associated with actual fraud The timestamp might be when the signator asserts that he signed a document or maybe when he wants the signature to go into effect In situations where it is critical that a signature be trusted to have the actual correct date people can simply use notaries to witness and date a handwritten signature The analog to this in digital signatures is to get a trusted third party to sign a signature certificate applying a trusted timestamp No exotic or overly formal protocols are needed for this Witnessed signatures have long been recognized as a legitimate way of determining when a document was signed A trustworthy Certifying Authority or notary co
72. emote timesharing system Keep a backup copy of both keyrings Not Quite Deleted Files Another potential security problem is caused by how most operating systems delete files When you encrypt a file and then delete the original plaintext file the operating system doesn t actually physically erase the data It merely marks those disk blocks as deleted allowing the space to be reused later It s sort of like discarding sensitive paper documents in the paper recycling bin instead of the paper shredder The disk blocks still contain the original sensitive data you wanted to erase and will probably eventually be overwritten by new data at some point in the future If an attacker reads these deleted disk blocks soon after they have been deallocated he could recover your plaintext In fact this could even happen accidentally if for some reason something went wrong with the disk and some files were accidentally deleted or corrupted A disk recovery program may be run to recover the damaged files but this often means some previously deleted files are resurrected along with everything else Your confidential files that you thought were gone forever could then reappear and be inspected by whomever is attempting to recover your damaged disk Even while you are creating the original message with a word processor or text editor the editor may be creating multiple temporary copies of your text on the disk just because of its internal workings These tempo
73. encrypted using the appropriate type key for each individual However in order for users of older versions of PGP to be able to decipher or verify this e mail they will first need to upgrade to one of the patched versions which remove this limitation Another improvement in this version of PGP is the implementation of the PGP MIME standard for some of the plug ins that integrate PGP functions directly into popular e mail applications If you are using an e mail application which is supported by one of the plug ins offering PGP MIME you will be able to encrypt and sign as well as decrypt and verify your e mail messages and file attachments automatically when you send or receive e mail However sending PGP MIME e mail to those who are not using an e mail application that supports this standard may be less convenient for them to decrypt and verify Upgrading from a Previous Version If you are upgrading from a previous version of PGP from either PGP Inc or ViaCrypt you may want to remove the old program files before installing PGP to free up some disk space However you should be careful not to delete the private and public keyring files used to store any keys you have created or collected while using the previous version When you install PGP you are given the option of retaining your existing Chapter 2 Getting Started private and public keyrings so you won t have to go through the trouble of importing all of your old keys To upgrade
74. eneTZQ3KEJuqswiNKiGlO0KxcilTehYIpxvRXlbfm3LAWCyUSFSPAbHS6E 0AJ3 2 To decrypt and verify the contents of the e mail message click the opened envelope button in your application s toolbar ale xl The PGP Enter Passphrase dialog box appears requesting that you enter your passphrase PGP Enter Passphrase i2 x Passphrase of selected key v Hide Typing a 3 Enter your passphrase and then click OK The message is decrypted and if the message is signed a panel appears indicating whether it is valid 4 Atthis point you can save the message in its decrypted state or you can save the original encrypted version so that it remains secure 52 Chapter 4 Sending and Receiving Private E mail Decrypting and Verifying Via the Clipboard If your e mail application is not supported by the PGP plug ins you must copy the contents of your message to the clipboard in order to decrypt it or to verify any digital signatures If the e mail contains file attachments you decrypt and verify them through the Windows Explorer To decrypt and verify using the clipboard l Inthe editor supplied with your e mail application select the encrypted text and then copy it to the clipboard In most applications choose Copy from the Edit menu to copy the text to the Windows clipboard 2 Click the lock and key icon in the System Tray to open the PGP pop up menu Choose Decrypt Verify Clipboard to initiate the decryption and verific
75. enever they need to sign or decrypt mail E mail Preferences Click the e mail tab to advance to the pane where you specify preferences that affect the way PGP functions are implemented for those e mail applications that are supported by the PGP plug ins You should note that the PGP MIME option is not applicable for all e mail applications PGP Preferences HEI General Key Files Email KeyServer m Email Preferences MV Word wrap clear signed messages at column 78 Encrypt new messages by default Sign new messages by default Cancel Help Use PGP MIME When Sending e mail When this check box is selected you do not have to go through the trouble of explicitly turning on the PGP MIME feature every time you send e mail For instance if you are using Eudora and you turn this setting on all of your e mail messages and file attachments are auto matically encrypted and signed to the intended recipi ent This setting has no effect on other encryptions you PGP for Personal Privacy Version 5 0 User s G uide for W indows 11 perform from the clipboard or with the Windows Explorer and should not be used if you plan to send e mail to recipients who use e mail applications that are not supported by the PGP MIME standard Although these users can decrypt and verify this type of message they will not be able to verify clear signed messages Word wrap clear signed messages at column
76. ent built encryption device called the Clipper chip containing a new classified NSA encryption algorithm The government has been trying to encourage private industry to design it into all their secure communication products like secure phones secure FAX etc AT amp T has put Clipper into their secure voice products The catch At the time of manufacture each Clipper chip will be loaded with its own unique key and the government gets to keep a copy placed in escrow Not to worry though the government promises that they will use these keys to read your traffic only when duly authorized by law Of course to make Clipper completely effective the next logical step would be to outlaw other forms of cryptography The government initially claimed that using Clipper would be voluntary that no one would be forced to use it instead of other types of cryptography But the public reaction against the Clipper chip has been strong stronger than the government anticipated The computer industry has monolithically proclaimed its opposition to using Clipper FBI director Louis Freeh responded to a question in a press conference in 1994 by saying that if Clipper failed to gain public support and FBI wiretaps were shut out by non government controlled cryptography his office would have no choice but to seek legislative relief Later in the aftermath of the Oklahoma City tragedy Mr Freeh testified before the Senate Judiciary Chapter 6 Security Fe
77. erform Many of the dialog boxes also have context sensitive help which you can use by simply clicking the question mark in the right corner of the window and then pointing to the area of interest on the screen for a short explanation Quitting PGP By default the PGP program runs whenever you start your computer as indicated by the lock and key icon which is displayed in the System tray If for some reason you need to quit running PGP from the System tray you can do so by choosing the Quit PGP option from the PGP pop up menu PGP for Personal Privacy Version 5 0 User s Guide for W indows 15 16 Using PGP from Supported E mail Applications If you have one of the popular e mail applications supported by the PGP plug ins you can access the necessary PGP functions by clicking the appropriate buttons in your application s toolbar For example you click the lock icon to indicate that you want to encrypt your message and the quill icon to indicate that you want to sign it 2 ale When you receive e mail from another PGP user you decrypt the message and verify the person s digital signature by clicking the opened envelope alo wl The key and envelope button will add any keys included in the message onto your keyring You can also access the PGPkeys window at any time while composing or retrieving your mail by clicking the double keys button To make things even simpler if you are using an e mail application with one of the plug
78. erify Your Email When someone sends you encrypted email you can unscramble the contents and verify any appended signature to make sure that the data originated with the alleged sender and that it has not been altered f you are using an email application that is supported by the plug ins you can decrypt and verify your messages by selecting the appropriate options from your application s tool bar In addition if your email application supports the PGP MIME standard you can decrypt and verify messages and file attachments sent using this format by clicking on an icon when reading your mail If your email application is not supported by the plug ins you can copy the message to the clipboard and perform the appropriate functions from there If you want to decrypt and verify file attachments you can do so from the Windows Explorer Chapter 1 Introducing PGP for Personal Privacy About This Manual This manual is organized in the following manner Chapter 1 Introducing PGP for Personal Privacy Describes the purpose of the program delves into the concept of public key encryption and digital signatures and provides a quick overview of how you will use the program Chapter 2 Getting Started Runs through the steps needed to install and run the PGP program with a brief discussion of the main components and primary functions Chapter 3 Making and Exchanging Keys Explains how to generate your private and public key pair and describes
79. ers is revealing of their agenda And the defeat of this plan isn t so reassuring when you consider that the 1994 Digital Telephony bill was also defeated the first time it was introduced in 1993 PGP for Personal Privacy Version 5 0 User s Guide for W indows 83 84 Advances in technology will not permit the maintenance of the status quo as far as privacy is concerned The status quo is unstable If we do nothing new technologies will give the government new automatic surveillance capabilities that Stalin could never have dreamed of The only way to hold the line on privacy in the information age is strong cryptography You don t have to distrust the government to want to use cryptography Your business can be wiretapped by business rivals organized crime or foreign governments The French government for example is notorious for using its signals intelligence apparatus against US companies to help French corporations get a competitive edge Ironically US government restrictions on cryptography have weakened US corporate defenses against foreign intelligence and organized crime The government knows what a pivotal role cryptography is destined to play in the power relationship with its people In April 1993 the Clinton administration unveiled a bold new encryption policy initiative which was under development at National Security Agency NSA since the start of the Bush administration The centerpiece of this initiative is a governm
80. essages and file attachments Plaintext Normal legible unencrypted unsigned text Private Key The secret portion of a key pair used to sign and decrypt information A user s private key should be kept secret known only to the user Private Keyring A set of one or more private keys all of which belong to the owner of the private keyring Public Key One of two keys in a key pair used to encrypt information and verify signatures A user s public key can be widely disseminated to colleagues or strangers Knowing a person s public key does not help anyone discover the corresponding private key Public Keyring A set of public keys Your public keyring includes your own public key s Public Key Cryptography Cryptography in which a public and private key pair is used and no security is needed in the channel itself A Glossary of Terms Sign To apply a signature Signature A digital code created with a private key Signatures allow authentication of information by the process of signature verification When you sign a message or file the PGP program uses your private key to create a digital code that is unique to both the contents of the message and your private key Anyone can use your public key to verify your signature Text Standard printable 7 bit ASCII text Trusted A public key is said to be trusted by you if it has been certified by you or by someone you have designated as an introducer User ID A text phra
81. examing keys properties Created 62 Enabled 63 Expire 62 Fingerprint 63 Key ID 62 Key Type 62 Trust Model 62 examining keys properties 62 Change Passphrase 63 Keys label 59 opening 14 Size label 60 Trust label 59 uses 58 Validity label 59 platforms supported 7 preferences decryption 75 email 77 encryption 74 general 74 key files 76 key generation 75 key server 79 passphrase cache 75 setting 74 Index Privacy Enhanced Mail 100 private and public key pairs creating 3 creating with PG P Key Wizard 14 viewing your 14 private key 108 private keys creating 3 key pairs 3 creating with PG P Key Wizard 14 location of 57 overview 2 protecting 33 34 setting location of 77 storing 33 34 viewing your 14 properties viewing a keyring s 62 protecting your keys 33 34 public key cryptography overview 2 public keys advantages of sending to key server 35 certifying 3 96 consequences of sending to key server 31 copying from email messages 39 creating 3 key pairs 3 creating with PG P Key Wizard 14 distributing your 35 exchanging with other users 3 exporting to files 37 getting from a key server 39 giving to other users 3 importing from files 40 including in an email message 37 location of 57 obtaining others 38 40 overview 2 protecting 33 34 sending to key server 31 35 36 setting location of 76 signing 66 96 storing 33 34 trading with other users 3 validating 3 viewing your 14 pubring
82. eys and your public keys are stored in separate keyring files which you can copy just like any other files to another location on your hard drive or to a floppy disk By default the private keyring secring pgp and the public keyring pubring pgp are stored along with the other program files in the PGP file directory but you can save your backups in any location you like PGP for Personal Privacy Version 5 0 User s Guide for Windows 33 34 When you specify that you want to save a backup copy of your keys the Select Backup Destination dialog box appears asking you to specify the location of the private and public keyring files that are to be backed up Select Backup Destination 2 x Savejm z Desktop fal e EJ E My Computer PNQui ese rs Network Neighborhood fa randseed bin J start Mi Registration Ah America Online ia secting bak i secting pap secting2 pap Besides making backup copies of your keys you should be especially careful about where you store your private key Even though your private key is protected by a passphrase that only you should know it is possible that someone could discover your passphrase and then use your private key to decipher your e mail or forge your digital signature For instance somebody could look over your shoulder and watch the keystrokes you enter or intercept them on the network or even over the airwaves To prevent anyone who might happen to get hold of your passphra
83. f PGP represents a significant rewrite of the original program and incorporates a completely new user interface it has been designed to be compatible with earlier versions of PGP This means that you can exchange secure e mail with those who are still using these older versions of the product PGP 2 6 Released by MIT PGP 4 0 Released by Viacrypt PGP 4 5 Released by PGP Inc PGP for Personal Privacy Version 5 0 User s Guide for W indows Along with the new user interface and other improvements one of the distinct differences between this version of PGP and its predecessors is the ability to generate a new type of key In addition to the RSA keys used by previous versions PGP gives you the option of using keys based on the DSS Diffie Hellman encryption and digital signature technologies Although the DSS Diffie Hellman keys are provided as an alternative to the traditional RSA keys you can take advantage of these newer keys only if you are exchanging e mail with another user who is using a version of PGP which is capable of recognizing these new keys Considering that it will take a while before the DSS Diffie Hellman keys gain widespread use in the user community you may want to reserve a set of RSA keys so that you can continue to communicate with those who have earlier versions of PGP If you are encrypting e mail to multiple recipients where some have RSA keys and others have DSS Diffie Hellman keys the e mail will be
84. from a previous version follow the appropriate steps listed below Upgrading from PGP 2 6 2 MIT Freeware l 2 Make sure that you have exited all programs currently running on your computer Locate and make backups of your old PGP keyrings on another volume Your public keys are stored in pubring pgp and your private keys are stored in secring pgp NOTE You may want to make two separate backups of your keyrings onto two different floppy disks just to be safe You must be especially careful not to loose your private keyring otherwise you will never be able to decrypt any e mail messages or file attachments encrypted with the lost keys Store the keyrings in a secure place where no one but you has access to them Once you have successfully backed up your old keyrings remove or archive the old PGP 2 6 2 software from on your hard disk You have two options here Manually delete the entire old PGP262 directory and all of its contents Manually delete the pgp exe 262 program and archive the remaining files especially the config txt and keyring files NOTE Ifyou obtain a copy of the newly patched PGP264 version from MIT your old 2 6 x software will be able to read the RSA keys on the new 5 0 keyrings and will not fail when it encounters the new DSS Diffie Hellman format keys Install PGP 5 0 using the provided InstallShield executable When the installer asks you if you have existing keyrings click on yes
85. g to either encrypt and or sign or you are going to use PGP MIME on a regular basis you can leave these operations turned on by selecting the appropriate settings from the e mail pane of the Preferences dialog box 3 Send your e mail message as you normally do Chapter 4 Sending and Receiving Private E mail If you have elected to sign the encrypted data the Passphrase dialog box appears requesting your passphrase before the mail is sent PGP Signing Passphrase HEI Signing key Michael J lannamico lt mji pgp com gt Enter passphrase IV Hide Typing A zd DK Cancel OK 4 Enter your passphrase and then click OK As long as you have a copy of the public keys for every one of the recipients the appropriate keys are used However if you specify a recipient for whom there is no corresponding public key the PGP Key Selection dialog box appears so you can specify the correct key PGPmail Key Selection Dialog 2 x Drag users from this list to the Recipients list amp Michael lannamico lt mji pap com gt 2048 1024 amp Philip R Zimmermann lt prz acm org gt mmm 1024 validity Tust Size Michael J lannamico lt mji pgp com gt 2048 Options Tw Text Got Cancel Help 5 Drag the public keys for those who are to receive a copy of the encrypted e mail message into the Recipients list box You can also double click on any of the keys to
86. h tells the world to no longer trust that version of your key See Chapter 5 for more details on how to revoke a key Chapter 3 Making and Exchanging Keys Including your Public Key in an E mail Message Another convenient method of delivering your public key to someone is to include it along with your e mail message To include your public key in an e mail message 1 Open the PGPkeys window by clicking on the lock and key icon in the Win95 tray or click the Start button and choose PGPkeys from the PGP submenu of the Programs menu 2 Select your key pair and then choose Copy from the Edit menu 3 Open the editor you use to compose your e mail messages place the cursor in the desired area and then choose Paste from the Edit menu In newer e mail applications you can simply drag your key from the PGPkeys window into the text of your e mail message to transfer the key information When you send someone your public key be sure to sign the e mail That way the recipient can verify your signature and be sure that no one has tampered with the information along the way Exporting your Public Key to a File Another method of distributing your public key is to copy it to a file and then make this file available to the person with whom you want to communicate There are several ways to copy your public key to a file e Select the icon representing your key pair from the PGPkeys window then choose Export from the Keys menu and enter t
87. he name of the file where you want the key to be saved Drag the icon representing your key pair from the PGPkeys window and drop it into the desired location in the Windows Explorer window e Select the icon representing your key pair in the PGPkeys window choose Copy from the Edit menu and then choose Paste to insert the key information into a text document PGP for Personal Privacy Version 5 0 User s Guide for W indows 37 Obtaining the Public Keys of Others Just as you need to distribute your public key to those who want to send you encrypted mail or to verify your digital signature you need to obtain the public keys of others so you can send them encrypted mail or verify their digital signatures You have several alternatives for obtaining someone s public key Get the key from a public key server Add the public key directly from an e mail message Import the public key from a file Since public keys are really just blocks of text they are really quite easy to add to your keyring by importing them from a file or copying them from an e mail message and then pasting them into your public keyring Here is an example of a public key block of text hogMas MCpkEOAAAEIALQiOUPrbStLJYfU7GGOXXlQwrEkunvibLBS8csCdfem9qPzK gUZolEgBTE6RstgNyYEPQjMXnlYOzUBvRuag6WJdlJlpJ8 AFWVOUACYUbxq8Vro 4b4RnMD7bjvy68MalGVVO07vC2 jx yx9FeQxlMABUrYvxrflzLt9BS8ePG5CEjfcY AgCOCc 6CWSizWUlvwupNtVuirDJdF6TCkmQ K3gdbmUuHByxSo2PlnG9jvacr4vh U
88. he government to outlaw cryptography one measure we can apply is to use cryptography as much as we can now while it is still legal When use of strong cryptography becomes popular it s harder for the government to criminalize it Thus using PGP is good for preserving democracy If privacy is outlawed only outlaws will have privacy Intelligence agencies have access to good cryptographic technology So do the big arms and drug traffickers But ordinary people and grassroots political organizations mostly have not had access to affordable military grade public key cryptographic technology Until now PGP empowers people to take their privacy into their own hands There s a growing social need for it That s why I created it PGP for Personal Privacy Version 5 0 User s Guide for W indows 85 86 Encryption Basics First some elementary terminology Suppose you want to send a message to a colleague whom we ll call Alice and you don t want anyone but Alice to be able to read it As shown in Figure 1 you can encrypt or encipher the message which means scrambling it up in a hopelessly complicated way rendering it unreadable to anyone except you and Alice You supply a cryptographic key to encrypt the message and Alice must use the same key to decipher or decrypt it At least that s how it works in conventional secret key encryption A single key is used for both encryption and decryption This means that this key must be initially
89. he new public key You could send out one package containing both your new public key and the key compromise certificate for your old key What If You Lose Your Private Key Normally if you want to revoke your own private key you can use the Revoke command from the PGPkeys menu to issue a revocation certificate signed with your own private key But what can you do if you lose your private key or if your private key is destroyed You can t revoke it yourself because you must use your own private key to revoke it and you don t have it anymore You ask each person you signed your key to retire his her certification Then anyone attempting to use your key based upon the trust of one of your introducers will know not to trust your public key Chapter 6 Security Features and Vulnerabilities Beware of Snake Oil When examining a cryptographic software package the question always remains why should you trust this product Even if you examined the source code yourself not everyone has the cryptographic experience to judge the security Even if you are an experienced cryptographer subtle weaknesses in the algorithms could still elude you When I was in college in the early seventies I devised what I believed was a brilliant encryption scheme A simple pseudorandom number stream was added to the plaintext stream to create ciphertext This would seemingly thwart any frequency analysis of the ciphertext and would be uncrackable even to the
90. he screen However if you are sure that no one is watching over your shoulder and you would like to see the characters of your passphrase as you type clear the Hide Typing check box TIP Your passphrase should contain multiple words and may include spaces numbers and other printable characters Choose something that you can remember easily but that others won t be able to guess and keep in mind that the passphrase is case sensitive The longer your passphrase and the wider the variety of characters it contains the more secure it is Try to include equal quantities of upper and lowercase alphabetic characters numbers punctuation marks and so on 28 Chapter 3 Making and Exchanging Keys 13 Click Next to begin the key generation process The Key Generation Wizard indicates that it is busy generating your key Key Generation Wizard PGP is now generating your new key pair On a slow machine this could take several minutes Please be patient If you have just installed PGP now is the perfect time to fill out your registration card Generating second prime number Hoo If you have entered an inadequate passphrase a warning message appears before the keys are generated and you have the choice of accepting the bad passphrase or entering a more secure one before continuing If there is not enough random information upon which to build the key the PGP Random Data dialog box appears As instructed o
91. hen this setting is selected any unknown recipients will be retrieved from the public key server when you encrypt or verify your e mail providing that the keys have been stored on the server Reverts to the default server name and port number set tings for the key server PGP for Personal Privacy Version 5 0 User s G uide for W indows 79 80 Chapter 5 Managing KeysAnd Setting Chapter 6 Security Features and Vulnerabilities This chapter contains introductory and background information about cryptography written by Phil Zimmermann Whatever you do will be insignificant but it is very important that you do it Mahatma Gandhi Why I wrote PGP It s personal It s private And it s no one s business but yours You may be planning a political campaign discussing your taxes or having a secret romance Or you may be communicating with a political dissident in a repressive country Whatever it is you don t want your private electronic mail e mail or confidential documents read by anyone else There s nothing wrong with asserting your privacy Privacy is as apple pie as the Constitution The right to privacy is spread implicitly throughout the Bill of Rights But when the US Constitution was framed the Founding Fathers saw no need to explicitly spell out the right to a private conversation That would have been silly Two hundred years ago all conversations were private If someone else was within earshot y
92. ic keys to 37 importing keys from 71 importing public keys from 40 setting location of keyring files 76 fingerprint 94 Fingerprint property 63 fingerprints checking 65 comparing 41 G generating key pairs 22 keys setting preferences 75 granting trust for key validations 67 H hash function 94 Index importing keys from files 71 public keys from files 40 installing from disk 12 from the W eb 12 PGP 12 introducer 96 98 113 K Key ID property 62 key management window 102 key pairs creating 3 22 23 32 creating with PG P Key Wizard 14 description of 22 examining 14 generating 22 making 22 setting expiration of 27 specifying defaults 63 viewing your 14 key server getting someone s public key from 39 sending your public key to 31 35 36 setting preferences 79 using to circulate revoke keys 72 key size Diffie Hellman portion 27 DSS portion 27 setting 26 trade offs 26 Key Type property 62 keyrings changing attributes of 58 63 description of 57 location of 57 overview of 2 setting location of 76 storing elsewhere 57 viewing attributes of 58 63 viewing properties of 62 keys backing up 33 34 checking fingerprints 65 colors of 32 deleting 69 disabling 68 distributing 35 enabling 68 examining 14 62 exporting to files 72 generating 22 granting trust for validations 67 importing from files 71 managing 57 overview of 21 protecting 33 34 revoked 73 revoking 72 saving 33 34 setting locat
93. ified for many years Even today many UNIX systems worldwide use the Enigma cipher for file encryption in part because the government has created legal obstacles against using better algorithms They even tried to prevent the initial publication of the RSA algorithm in 1977 And they have for many years squashed essentially all commercial efforts to develop effective secure telephones for the general public The principal job of the US government s National Security Agency is to gather intelligence principally by covertly tapping into people s private communications see James Bamford s book The Puzzle Palace The NSA has amassed considerable skill and resources for cracking codes When people can t get good cryptography to protect themselves it makes NSA s job much easier NSA also has the responsibility of approving and recommending encryption algorithms Some critics charge that this is a conflict of interest like putting the fox in charge of guarding the hen house In the 1980s NSA had been pushing a conventional encryption algorithm that they designed the COMSEC Endorsement Program and they won t tell anybody how it works because that s classified They wanted others to trust it and use it But any cryptographer can tell you thata well designed encryption algorithm does not have to be classified to remain secure Only the keys should need protection How does anyone else really know if NSA s classified algorithm is secure It s not that h
94. ighly compromising bit of information By default this set ting is set to 120 seconds which is probably sufficient to perform most of your PGP chores without having to enter your passphrase too many times but not long enough for someone to determine your passphrase Cache Signing Passphrase for Seconds This setting specifies the amount of time in seconds that your signature passphrase is stored in your com puter s memory If you regularly compose or read sev eral e mail messages in succession you may want to increase the amount of time your passphrase is cached so you don t have to enter your passphrase over and over again to get through all of your mail Show Recipients When Encrypting To Marginally Valid Keys This setting specifies that you would like to be warned whenever you are encrypting to a recipient for which the validity is only marginally established Faster Key Generation When this setting is selected it requires less time to generate a new DSS Diffie Hellman key pair This pro cess is speeded up by using a previously calculated set of prime numbers rather than going through the time consuming process of creating them from scratch each PGP for Personal Privacy Version 5 0 User s Guide for Windows 75 time a new key is generated However you should note that fast key generation is only implemented for the fixed key sizes provided as options when you create a key and will not be utilized if you enter some
95. igital signature since it is a reasonably safe assumption that the person creating the key is in fact the true owner The reason for signing your own key is to prevent anyone from modifying it which would immediately invalidate your signature PGP users often have other trusted users sign their public keys to further attest to their authenticity For instance you might send a trusted colleague a copy of your public key with a request that they certify and return it so you can include their signature when you post your key on a public key server Now when someone gets a copy of your public key they don t necessarily have to check the key s authenticity themselves but can instead rely on how well they trust the person who signed your key PGP provides the means for establishing this level of trust for each of the PGP for Personal Privacy Version 5 0 User s Guide for W indows 41 42 public keys you add to your public keyring and shows the level of trust associated with each key in the PGPkeys window This means that when you get a key from someone whose key is signed by a trusted introducer you can be fairly sure that the key belongs to the purported user For details on how to sign keys and validate users see Chapter 5 Chapter 3 Making and Exchanging Keys Chapter 4 Sending and Receiving Private E mail This chapter explains how to encrypt and sign the e mail you send to others and decrypt and verify the e mail others send to y
96. igital signature standard that would preclude anyone from repudiating their signatures That has distinct benefits for law enforcement and intelligence gathering Also SHA has been published in the open literature and has been extensively peer reviewed by most of the best cryptographers in the world who specialize in hash functions and the unanimous opinion is that SHA is extremely well designed It has some design innovations that overcome all the observed weaknesses in message digest algorithms previously published by academic cryptographers All new versions of PGP use SHA as the message digest algorithm for creating signatures with the new DSS keys that comply with the NIST Digital Signature Standard For compatibility reasons new versions of PGP still use MD5 for RSA signatures because older versions of PGP used MD5 for RSA signatures The message digest algorithm used by older versions of PGP is the MD5 Message Digest Algorithm placed in the public domain by RSA Data Security Inc MD5 is a 128 bit hash algorithm In 1996 MD5 was all but broken by Hans Dobbertin a German cryptographer While MD5 was not completely broken at that time it was discovered to have such serious weaknesses that no one should keep using it to generate signatures Further work in this area might completely break it thus allowing signatures to be forged If you don t want to someday find your PGP digital signature on a forged confession you might be well advised
97. igned using your public key Similarly once you are sure that a key belongs the proper individual you can sign their public key indicating that you are sure it is a valid key To sign someone s public key l Select the key you want to sign 2 Choose Sign from the Keys menu The PGPkeys alert box appears PGPkeys RIES By signing the selected kev s you are certifying based on your own direct first hand knowledge that they belong to the selected user s Other people may rely on your signature and trust the key s as a result Sign the key s Send signature to keyserver Yes 3 Click Yes to indicate your certainty that the key does indeed belong to the purported owner If you would like to send the key with your signature to the key server check the Send signature to keyserver checkbox The public key on the server will subsequently be updated to reflect the inclusion of your signature Since most users prefer to use their own discretion when allowing others to sign their keys it is always a good idea to check with the owner before you add your signature to their key on the server 66 Chapter 5 Managing Keys And Setting You will then be asked to enter the passphrase for your default key pair PGP Signing Passphrase HEI Signing key Michael J lannamico lt mji pgp com gt x Enter passphrase IV Hide Typing I x Ga 4 Enter your passphrase and then click OK If you have another key pair that
98. in bold text to distinguish these keys from your other keys PGP for Personal Privacy Version 5 0 User s Guide for W indows 63 To specify your default key pair l Select the key pair you want designated as your default pair 2 Choose Set As Default Key from the Keys menu The selected key bold faced indicating that it is now designated as your default key pair Adding a New User Name or Address In some cases you may have more than one user name or e mail address for which you want to use the same set of keys After initially creating a new set of keys you can add alternate names and addresses to the key You can only add a new user name or e mail address when you have both the private and public keys To add a new user name or address to an existing key l Select the key pair for which you want to add another user name or address 2 Choose Add Name from the Keys menu The PGP New User Name dialog box appears PGP New User Name 21x New name to add to key New email address to add to key predamo OK Cancel 3 Enter the new name then press Tab to move to the next field 4 Enter the new e mail address 5 Click OK after you have entered the new name and address Chapter 5 Managing KeysAnd Setting The PGP Enter Passphrase dialog box appears requesting that you enter your passphrase PGP Enter Passphrase i2 x Passphrase of selected key Iv Hide Typing l Gees 6 Enter you passphrase
99. information or retain it in its encrypted form PGP for Personal Privacy Version 5 0 User s Guide for W indows 13 Opening the PGPkeys Window By choosing the Launch PGPkeys option from the PGP pop up menu you open the PGPkeys window that shows the private and public key pairs you have created for yourself as well as any public keys you have added to your public keyring If you have not already created a new key pair the PGP Key Wizard leads you through the steps necessary to create a new key pair However before going through the process of creating a new key pair you should see Chapter 3 for complete details regarding the various options vi PGPkeys D x File Edi Keys Help uL vaidiy_ _Tust_ Ceaton_ Sie _ __ E Qe Brett A Thomas lt bat pgp com gt 5 18 97 1024 2048 E D Carolyn Turbyfill lt turby pap com gt 4 8 97 1024 2048 Damon Gallaty lt dgal pgp com gt 5 20 97 1024 3072 E amp Dave Heller lt dheller pagp com gt 5 20 97 1024 2048 DJ Young DSS di pgp com 5 16 97 1024 2048 Lloyd L Chambers lt lloyd pagp com gt 5 20 97 1024 4096 Mark J McArdle lt markm pgp com gt 5 15 97 1024 2048 Qe Michael lannamico lt mji pgp com gt 5 19 97 1024 4021 Qe PGP Support Key DSS lt pgpsupport p 5 20 97 1024 1024 Qe Philip R Zimmermann lt prz pgp com gt 4 7 97 1024 2048 Pretty Good Privacy Inc Corporate Key 6 3 97 1024 2048 E Qe Will Price lt wprice pgp com gt 6 3 97 102
100. ion of 76 setting size of 26 signing 66 types of DSS Diffie Hellman 8 22 RSA 8 22 verifying authenticity of 40 viewing properties of 62 L legitimacy determining a key s 40 M making key pairs 22 managing keys 57 memory system requirements 7 message digest 94 MIME standard using to decrypt email 51 52 PG P for Personal Privacy Version 5 0 User s Guide for W indows 123 using to encrypt email 43 46 new email address adding 64 O obtaining others public keys 38 40 opening PGPkeys window 14 overviews checking digital signature 2 cryptography 2 decrypting email 2 digital signature 2 encrypting email 2 key concepts 21 keyrings 2 private keys 2 public key cryptography 2 public keys 2 signing email 2 verifying digital signature 2 P pass phrase 108 passphrase Change Passphrase property 63 changing 69 forgotten 73 setting 28 setting preferences 75 suggestions for 28 PEM 100 PGP compatibility 7 history 7 installing 12 overview of 2 running 12 124 upgrading from a previous version 8 upgrading from PG P Inc 8 upgrading from ViaCrypt 8 using from the Clipboard 13 using from the System tray 13 ways to use 12 PGP Key Wizard creating key pairs 14 using to create key pairs 22 PG P MIME standard compatibility 8 using to decrypt email 51 52 using to encrypt email 43 46 PG Pkeys window creating key pairs with 23 32 Creation label 60 description 58
101. is simple enough to guess PGP is not designed to protect your data while it is in plaintext form on a compromised system Nor can it prevent an intruder from using sophisticated measures to read your private key while it is being used You will just have to recognize these risks on multi user systems and adjust your expectations and behavior accordingly Perhaps your situation is such that you should consider only running PGP on an isolated single user system under your direct physical control Traffic Analysis Even if the attacker cannot read the contents of your encrypted messages he may be able to infer at least some useful information by observing where the messages come from and where they are going the size of the messages and the time of day the messages are sent This is analogous to the attacker looking at your long distance phone bill to see who you called and when and for how long even though the actual content of your calls is unknown to the attacker This is called traffic analysis PGP alone does not protect against traffic analysis Solving this problem would require specialized communication protocols designed to reduce exposure to traffic analysis in your communication environment possibly with some cryptographic assistance Cryptanalysis An expensive and formidable cryptanalytic attack could possibly be mounted by someone with vast supercomputer resources such as a government intelligence agency They might crack yo
102. k to make sure that the key has not been tampered with and that it really belongs to the purported owner You do this by comparing the unique fingerprint on your copy of someone s public key to the fingerprint on their original key When you are sure that you have a valid public key you sign it to indicate that you feel the key is safe to use In addition you can grant the owner of the key a level of trust indicating how much confidence you have in them to vouch for the authenticity of someone else s public key PGP for Personal Privacy Version 5 0 User s Guide for W indows Encrypt and Sign Your Email After you have generated your key pair and have exchanged public keys you can begin encrypting and signing email messages and file attachments f you are using an email application supported by the plug ins you can encrypt and sign your messages by selecting the appropriate options from your application s tool bar In addition if you are communicating with other PGP users who are using a version which adheres to the PGP MIME standard you can encrypt and sign messages as well as file attachments automatically when you send your mail If your email application is not supported by the plug ins you can copy the message to the clipboard and perform the appropriate functions from there If you want to include any file attachments you can encrypt and sign them from the Windows Explorer before attaching them to your email Decrypt and V
103. keys window and choose Paste from the Edit menu to copy the key The key will then show up as an icon in the PGPkeys window Verifying the Authenticity of a Key When you exchange keys with someone it is sometimes hard to tell if the key really belongs to that person PGP provides a number of safeguards which allow you to check a key s authenticity and to certify that the key belongs to a particular owner The PGP program will also warn you when you attempt to use a key that is not valid and can be set to optionally warn you when you are about to use a marginally trusted key One of the major vulnerabilities of public key encryption systems is the ability of some eavesdropper to mount a man in the middle attack by replacing someone s public key with one of their own In this way they can intercept any encrypted e mail intended for that person decrypt it using their own key then encrypt it again with the person s real key and send it on to them as if nothing had ever happened In fact this could all be done automatically through a sophisticated computer program that stands in the middle and deciphers all of your correspondence Chapter 3 Making and Exchanging Keys Based on this scenario you and those with whom you exchange e mail need a way to determine whether you do indeed have legitimate copies of each others keys The best way to be completely sure that a public key actually belongs to a particular person is to have the owner copy
104. l you into accepting his own bogus key as Alice s because no one else can forge signatures made by David A widely trusted person could even specialize in providing this service of introducing users to each other by providing signatures for their public key certificates This trusted person could be regarded as a Certifying Authority Any public key certificates bearing the Certifying Authority s signature could be trusted as truly belonging to whom they appear to Chapter 6 Security Features and Vulnerabilities belong to All users who wanted to participate would need a known good copy of just the Certifying Authority s public key so that the Certifying Authority s signatures could be verified In some cases the Certifying Authority may also act as a key server allowing users on a network to look up public keys by asking the key server but there is no reason why a key server must also certify keys A trusted centralized Certifying Authority is especially appropriate for large impersonal centrally controlled corporate or government institutions Some institutional environments use hierarchies of Certifying Authorities For more decentralized environments allowing all users to act as trusted introducers for their friends would probably work better than a centralized key certification authority One of the attractive features of PGP is that it can operate equally well in a centralized environment with a Certifying Authority or a more
105. locate your old 262 keyrings and follow the instructions to copy those keys to your new PGP 5 0 keyrings Restart your computer PGP for Personal Privacy Version 5 0 User s Guide for W indows 10 Upgrading from PGPmail 4 0 This process is the same as with PGP 2 6 2 ViaCrypt PGP must be manually removed and or archived Be sure to keep backups of your keyrings See also the ReadMe file for PGP 4 0 1 for UNIX and DOS which describes the patched version for reading PGP 5 0 keyrings with the old ViaCrypt software Upgrading from PGPmail 4 5 1 Make sure that you have exited all programs processes currently running on your computer 2 End the PGP Enclyptor process enclypt_32 exe that may be running soit can be uninstalled To determine if the Enclyptor is running look for it s floating palette or it s minimized item in the Taskbar name The Enclyptor As an alternate method you can use Control Alt Delete to bring up the Task Manager select the process named The Enclyptor and click the End Task button Open the Start menu s Settings Control Panel item Double click Add Remove Programs Select the PGPmail 4 5 item u A Uu Click the Add Remove button Allow the Uninstall utility to automatically delete all the necessary files for you and clean up your Registry file NOTE If you are asked about whether to delete any dll files during the uninstall process it s safe to remove them The
106. mico mji amp pgp com i Cancel Help All you need do to select a recipients public key is to drag the icon representing their key into the Recipient s list box and then click OK For complete instructions on how to encrypt and sign and decrypt and verify e mail see Chapter 4 Taking Shortcuts While you will find that PGP is quite easy to use a number of shortcuts are available to help you accomplish your encryption tasks even quicker For instance while you are managing your keys in the PGPkeys window you can click the right mouse button to perform all of the necessary PGP functions rather than accessing them from the menu bar You can also drag a file containing a key into the PGPkeys window to add it to your key ring Keyboard shortcuts are also available for most menu operations Chapter 2 Getting Started which allow you to instigate a function by holding down the Ctrl key and some other key These keyboard shortcuts are shown on all of the PGP menus and the other shortcuts are described in their proper context throughout this manual PGP for Personal Privacy Version 5 0 User s Guide for W indows 19 20 Chapter 2 Getting Started Chapter 3 Making and Exchanging Keys This chapter describes how to generate the private and public key pairs that you need to correspond with other PGP users It also explains how to distribute your public key and obtain the public keys of others so that you can begin exchanging p
107. move them from one area of the screen to the other PGP for Personal Privacy Version 5 0 User s Guide for W indows 45 46 The Validity bar indicates the minimum level of confidence that the public keys in the Recipient list are valid This validity is based on the signatures associated with the key and the trust indicates how well you can rely on the owner of the key to vouch for the authenticity of another users key See Chapter 5 for more details NOTE Ifyou are not using PGP MIME you must encrypt any files you want to send as attachments from the Windows Explorer before sending them 6 Click OK to send your mail Encrypting and Signing Via the Clipboard If you are using an e mail application that is not yet supported by the PGP plug ins you must encrypt and sign your e mail via the Windows clipboard You do this by clicking on the lock and key icon located in the System Tray and then choosing the appropriate option Essentially you copy the contents of your message to the clipboard encrypt and or sign its contents then paste it into your e mail editor before sending it If you plan to attach any files with your message you must encrypt them from the Windows Explorer before attaching them To encrypt and sign via the clipboard Here is the procedure for encrypting and signing an e mail message using the clipboard 1 Use the editor supplied with your e mail application or your favorite word processing program to co
108. mpose the message you want to send 2 When you are ready to send the message select the area of text you want to encrypt or choose Select All from the Edit menu available in most applications 3 Choose Copy from the Edit menu to copy the contents of your message to the clipboard You should note that any time you copy or cut text in your application it is temporarily stored on the clipboard Chapter 4 Sending and Receiving Private E mail 4 Click the lock and key icon in the System tray and choose either Encrypt Clipboard Sign Clipboard or Encrypt And Sign Clipboard depending on the operations you want to perform If you indicate that you want to encrypt the contents of the clipboard the PGP Key Selection Dialog box appears PGPmail Key Selection Dialog 2 x Drag users from this list to the Recipients list amp Michael lannamico lt mji pap com gt 2048 1024 amp Philip R Zimmermann lt prz acm org gt r mmm 1024 Recipients vai Tus Sie Michael J lannamico lt mji pgp com gt 2048 5 Drag the public keys for those who are to receive a copy of the encrypted e mail message into the Recipients list box The Validity bar indicates the minimum level of confidence that the public keys in the Recipient list are valid This validity is based on the signatures associated with the key and the trust indicates how well you can rely on the owner of the key to vouch for the
109. n If you are receiving e mail from someone who is not using a PGP MIME compliant e mail application you will decrypt the e mail messages by clicking the open envelope icon in your application s toolbar Also if there are any encrypted file attachments you will decrypt them from the Windows Explorer PGP for Personal Privacy Version 5 0 User s Guide for W indows 51 To decrypt and verify with supported e mail applications 1 Open your e mail message as you normally do You will see a block of unintelligible ciphertext in the body of your e mail message Version 5 0 alpha MessageID ll2sx9zzduBjOiEXMCqGGfnxLWhzpn6wv hQ EMAxrO 0Jt4ElllhAQfSG KSInRxO0GXylocNl1s0USdzsEb h5x6DpmRDE4qsAME thh5bU TydGwCoHR74S3X4GaH5VAyxZzaryEB gt laLahe nrhi3rW NvijUPaAKi FS4Gq FhO091IYec RapRGzlcjBnzhKIhTbkjrdmoRxeRHnLl2VF9Am4GtRHdKctTl Akqg9z5TcxZS9yE r9qnzGpHNuUVtLVQBX3 WEsQvRPh7006GkSaKKAZGIDaiCXZzZu 6Wu3a9Sv8sR58QVl62z6Xl1VyrkLu S3ddrbJS82rneR4hMxjwCeevJuDMWhNHh6vNM lHb9WzU6 21 c dmmhPzfTka4jlaFuBYvwX7tEWWJoAWFKUBUcgVwY36icHjQeFa8qLs DbEnVeMV2rXY5Gdzsyg0S McOgO0qrMgToycQOwZzUw g00GBu5VjO0CGRZ4mSyvS6f DUvqYeEAJXfdkyXPOnUJSBS6 9BEw DABCSR3rQADV4vCOjElOUOD6qLIRFxVORA DmSGBCbulE97qgjWfsMFHcEnjqBlUVQRNEiuSRGxEoF STbHPR3nvPER6ASDYZEKSDc n mhKb4ujmqFAlc5LJJelCzEBdk4Z4fUJAJec c ufs56crLozGVzIbTXluVifXBTTc e 5uD0AalEe48JM6fv6O0zgFJZlYZ4IZZfdlWAG6cUx9GUmQtCMBX np34oALlFZWpe2t PfExS3PXNLOSXUSwTetVAvs bQ lZRPYJlIMPKLEPejpqxbbGgAlXDX2CvzZPCDvkO0O LkH
110. n the screen move your mouse around and enter a series of random keystrokes until the progress bar in the dialog box is completely filled in Your mouse movements and keystrokes generate random information that is needed to create a unique key pair After the key generation process begins it may take a while to generate the keys In fact if you specify a size other than the default values for a DSS Diffie Hellman key the fast key generation feature is not used and it could take hours to generate your key Eventually the Key Generation Wizard indicates that the key generation process has completed 14 Click Next to advance to the next dialog box PGP for Personal Privacy Version 5 0 User s Guide for W indows 29 30 If you are creating a key with the same user name or e mail address as a previous key you are given the opportunity to sign the new key with your older key This will endow the new key with same level of validity and trust as your older key when someone adds it to their keyring The validity is based on those who have signed the key in the past but it does not include the signatures from your old key Key Generation Wizard You have an old private key on your keyring with the same name and email address as the key you ve just generated We recommend that you now sign your new key with your old one To do so simply enter the passphrase to your old private key in the field below If you do not wish to sign y
111. nding and Receiving Private E mail Chapter 5 Managing Keys And Setting Preferences This chapter explains how to examine and manage the keys stored on your digital keyrings It also describes how to set your preferences to suit your particular computing environment Managing Your Keys The keys you create as well as those you collect from others are stored on digital keyrings which are essentially files stored on your hard drive or on a floppy disk Normally your private keys are stored in a file named secring skr and your public keys are stored in another file named pubring pkr These files are usually located in the same program directory as the other PGP program files The following icons are used to represent your private and public keyring files making them easy to distinguish when you are browsing through your files R amp Private Keyring Public Keyring NOTE Inthe event you have more than one key pair or if you are not comfort able storing your keys in the usual place you can choose a different file name or location See Setting Your Preferences PGP for Personal Privacy Version 5 0 User s Guide for W indows 5 58 On occasion you may want to examine or change the attributes associated with your keys For instance when you obtain someone s public key you might want to identify its type either RSA or DSS Diffie Hellman check its fingerprint or determine its validity based on any digital signatures include
112. new PGP 5 0 software will install newer versions of those files 7 Click on OK to complete the removal and dismiss the Add Remove panel when complete 8 Install the new PGP 5 0 software using the provided InstallShield utility It s recommended but not mandatory to direct the installer to the default install directory Chapter 2 Getting Started When the installer asks you if you have existing keyrings click on yes locate your old PGP 4 5 keyrings and follow the instructions to copy those keys to your new PGP 5 0 keyrings 10 Restart your computer Upgrading from previous beta versions of PGPmail 5 0 l ao u FF Uu Make sure that you have exited all programs processes currently running on your computer End the PGPtray task that may be running so it can be uninstalled To determine if PGPtray exe is running check in the Tray area of the Taskbar for a small PGP envelope icon if present PGPtray is running To end the task click on the PGP tray icon and select the Quit PGPtray command at the bottom of the menu You can also use Control Alt Delete to bring up the Task Manager select the Pgptray process and click the End Task button Open the Start menu s Settings Control Panel item Double click on Add Remove Programs Select the PGP 5 0bNN item Click the Add Remove button NOTE If you are asked whether to delete any dll files during the uninstall process it s safe to remove them
113. ng another version of PGP the first thing you need to do before sending or receiving encrypted and certified e mail is create a new key pair A key pair consists of two keys a private key that only you possess and a public key that you freely distribute to those with whom you correspond You generate a new key pair from the PGPkeys window using the PGP Key Wizard which guides you through the process Chapter 3 Making and Exchanging Keys To create a new key pair 1 Either click the Start button and then choose PGPkeys from the PGP submenu of the Programs menu or click the lock and key icon in the System tray and choose Launch PGPkeys You can also open this window by clicking the double keys icon located in your e mail application s toolbar The PGPkeys window opens File Edit Keys Help Keys _________ El Tus E Gesn lse Qe Brett Thomas lt bat pgp com gt 5 18 97 1024 2048 Qe Carolyn Turbyfill lt turby pgp com gt 4 8 37 1024 2048 Damon Gallaty dgal pgp com 5 20 97 1024 3072 Qe Dave Heller lt dheller pgp com gt 5 20 97 1024 2048 Qe DJ Young DS5 lt dj pap com gt 5 16 97 1024 2048 Qe Lloyd L Chambers lt lloyd pgp com gt 5 20 97 1024 4096 Qs Mark J McArdle lt markm pgp com gt 5 15 97 1024 2048 Michael lannamico lt mji pgp com gt 5 19 97 1024 4021 Qe PGP Support Key DSS lt pgpsupport p 5 20 97 1024 1024 Qe Philip R Zimmermann lt prz pgp com gt 4 7 97 1024 2048 Qe Pretty Good Privacy Inc
114. not been altered in any way during transit In the same way if you want to verify somebody else s digital signature or check the integrity of the e mail they send to you then you need a copy of their public key to do so This version of PGP supports two distinct types of keys the traditional RSA key used in older versions of PGP and a new type of key called DSS Diffie Hellman which is based on the latest advancements in cryptographic technologies If you plan to exchange e mail with someone who has PGP for Personal Privacy Version 5 0 or later then you can take advantage of the new DSS Diffie Hellman keys However if you are corresponding with someone who is using a previous version of PGP you have to use the traditional RSA keys to communicate with them NOTE Ifyou are upgrading from an earlier version of PGP you have probably already generated a private key and have distributed its matching public key to those with whom you correspond In this case you don t have to make a new key pair as described in the next section Instead you should have specified the location of your keys during the installation process and your keys will show up when you open the PGPkeys window If you have existing keys and did not specify their location during the installation you can go to the Key Files pane of the Preferences dialog box and enter the correct path to your existing keys Making a Key Pair Unless you have already done so while usi
115. osystems Advances in Computer Security Vol III edited by Rein Turn Artech House 1988 Chapter 6 Security Features and Vulnerabilities Glossary A Glossary of Terms ASCII Armored Text Binary information that has been encoded using a standard printable 7 bit ASCII character set for convenience in transporting the information through communication systems In the PGP program ASCII armored text files are given the asc default filename extension and they are encoded and decoded in the ASCII radix 64 format Authentication The determination of the origin of encrypted information through the verification of someone s digital signature or someone s public key by checking its unique fingerprint Certify To sign another person s public key Certifying Authority One or more trusted individuals are assigned the responsibility of certifying the origin of keys and adding them to a common database Decryption A method of unscrambling encrypted information so that it becomes legible again The recipient s private key is used for decryption Digital Signature See signature Encryption A method of scrambling information to render it unreadable to anyone except the intended recipient who must decrypt it to read it Introducer A person or organization who is allowed to vouch for the authenticity of someone s public key You designate an introducer by signing their public key Key A digital code used to encrypt and sign and d
116. other value Although it would be just about impossible for anyone to ever crack your key based on their knowl edge of these canned prime numbers some may want to spend the extra time to create a key pair with the maximum level of security Key Files Preferences Click the Key Files tab to advance to the pane in which you specify the location of the keyrings used to store your private and public keys PGP Preferences 21 x General Key Files Email KeyServer r Public Key Ring File C Program Files PGP PGP50 pub pubk Browse Private Key Ring File c Program Files PGP PGP50 secring skr Browse Cancel Help Public Key Ring File Shows the current location and name of the file where the PGP program expects to find your public keyring file If you plan to store your public keys in a file with a different name or in some other location you specify this information here You can use the Browse button to search through your files rather than having to explic itly type the path Chapter 5 Managing Keys And Setting Private Key Ring File Shows the current location and name of the file where the PGP program expects to find your private keyring file If you plan on storing your private keys in a file with a different name or in some other location you specify this information here Some users like to keep their private keyring on a floppy disk which they insert like a key wh
117. ou Encrypting and Signing E mail The quickest and easiest way to encrypt and sign e mail is with an application supported by the PGP plug ins Although the procedure varies slightly between different e mail applications you perform the encryption and signing process by clicking the appropriate buttons in the application s toolbar In addition if you are using an application which supports the PGP MIME standard you can encrypt and sign your e mail messages as well as any file attachments when you send or receive your e mail If you are using an e mail application that is not supported by the PGP plug ins you can encrypt and sign your e mail messages via the Windows clipboard by selecting the appropriate option from the lock and key icon located in the System Tray To include any file attachments you encrypt the files from the Windows Explorer before attaching them Encrypting and Signing with Supported E mail Applications When you are encrypting and signing with an e mail application that is supported by the PGP plug ins you have two choices depending on what type of e mail application the recipient is using If you are communicating with other PGP users who have an e mail application that supports the PGP MIME standard you can take advantage of a PGP MIME feature to PGP for Personal Privacy Version 5 0 User s Guide for W indows 43 44 encrypt and sign your e mail messages and any file attachments automatically when you
118. ou could just go out behind the barn and have your conversation there No one could listen in without your knowledge The right to a private conversation was a natural right not just in a philosophical sense but in a law of physics sense given the technology of the time But with the coming of the information age starting with the invention of the telephone all that has changed Now most of our conversations are conducted electronically This allows our most intimate conversations to PGP for Personal Privacy Version 5 0 User s Guide for W indows 81 82 be exposed without our knowledge Cellular phone calls may be monitored by anyone with a radio Electronic mail sent across the Internet is no more secure than cellular phone calls E mail is rapidly replacing postal mail becoming the norm for everyone not the novelty it was in the past And e mail can be routinely and automatically scanned for interesting keywords on a large scale without detection This is like driftnet fishing Perhaps you think your e mail is legitimate enough that encryption is unwarranted If you really are a law abiding citizen with nothing to hide then why don t you always send your paper mail on postcards Why not submit to drug testing on demand Why require a warrant for police searches of your house Are you trying to hide something If you hide your mail inside envelopes does that mean you must be a subversive or a drug dealer or maybe a paranoid
119. our new key with your old one now uncheck Sign my new key now and press Nest You can always sign your new key at a later date from within PGPkeys Old Private Key Passphrase M Hide Typing 15 If applicable sign your new key with the older key and enter the passphrase for the old key then click Next Chapter 3 Making and Exchanging Keys The Key Generation Wizard indicates that you have successfully generated a new key pair and asks you if you want to send your public key to the public key server Key Generation Wizard If you have an Internet connection we suggest that you send your new key to the keyserver p This will make it easy for your correspondents to get your key and communicate with you securely B If you don t have an Internet connection or are not connected right now leave Send my key to the keyserver now unchecked You can send your key later from within PGPkeys NN B N Beck Cancel Heb 16 Specify whether you want your new public key to be sent to the key server and then click Next By sending your public key to the key server anyone will be able to get a copy of your key when they need it For complete details see the section Distributing Your Public Key later in this chapter PGP for Personal Privacy Version 5 0 User s Guide for W indows 31 When the Key Generation process completes the final dialog box appears Key Generation Wizard
120. procedures to follow that can greatly reduce the chances of viral infection A complete treatment of anti viral and anti worm countermeasures is beyond the scope of this document PGP has no defenses against viruses and assumes your own personal computer is a trustworthy execution environment If such a virus or worm actually appeared hopefully word would soon get around warning everyone Another similar attack involves someone creating a clever imitation of PGP that behaves like PGP in most respects but doesn t work the way it s supposed to For example it might be deliberately crippled to not check signatures properly allowing bogus key certificates to be accepted You should make an effort to get your copy of PGP directly from Pretty Good Privacy There are other ways to check PGP for tampering using digital signatures You could use another trusted version of PGP to check the signature on a suspect version of PGP But this will not help at all if your operating system is infected nor will it detect if your original copy of pgp exe has been maliciously altered in such a way as to compromise its own ability to Chapter 6 Security Features and Vulnerabilities check signatures This test also assumes that you have a good trusted copy of the public key that you use to check the signature on the PGP executable Swap Files or Virtual Memory PGP was originally developed for MS DOS a primitive operating system by today s standards Bu
121. r each use Nonetheless it seems prudent to try to keep it from falling into the wrong hands If possible make the file readable only by you If this is not possible do not let other people indiscriminately copy disks from your computer How Decryption Works As shown in Figure 4 the decryption process is just the reverse of encryption The recipient s private key is used to recover the temporary session key and then that session key is used to run the fast conventional secret key algorithm to decipher the large ciphertext message PGP for Personal Privacy Version 5 0 User s Guide for W indows 91 Figure 4 Recipient s Private Key 0100000101000011 4 5 Session Key Encrypted L IS SessinniKey Decryption Using Public Key Encrypted i Decryption Using Plainte Message Conventional Messag Secret Key Using PGPmail recipient recovers session key and decrypts the file or message in a single operation How Digital Signatures Work PGP uses digital signatures to provide message authentication The sender s own private key can be used to encrypt a message digest thereby signing the message A message digest is a 160 bit or a 128 bit cryptographically strong one way hash function It is somewhat analogous to a checksum or CRC error checking code in that it compactly represents the message and is used to detect changes in the message Unlike a CRC
122. rary copies of your text are deleted by the word processor when it s done but these sensitive fragments are still on your disk somewhere PGP for Personal Privacy Version 5 0 User s Guide for W indows 109 110 The only way to prevent the plaintext from reappearing is to somehow cause the deleted plaintext files to be overwritten Unless you know for sure that all the deleted disk blocks will soon be reused you must take positive steps to overwrite the plaintext file and also any fragments of it on the disk left by your word processor You can take care of any fragments of the plaintext left on the disk by using any of the disk utilities available that can overwrite all of the unused blocks on a disk For example the Norton Utilities for MS DOS can do this Viruses and Trojan Horses Another attack could involve a specially tailored hostile computer virus or worm that might infect PGP or your operating system This hypothetical virus could be designed to capture your Passphrase or private key or deciphered messages and covertly write the captured information to a file or send it through a network to the virus s owner Or it might alter PGP s behavior so that signatures are not properly checked This attack is cheaper than cryptanalytic attacks Defending against this falls under the category of defending against viral infection generally There are some moderately capable anti viral products commercially available and there are hygienic
123. ressed For the technically curious the program uses the freeware ZIP compression routines written by Jean Loup Gailly Mark Adler and Richard B Wales This ZIP software uses compression algorithms that are functionally equivalent to those used by PKWare s PKZIP 2 x This ZIP compression software was selected for PGP mainly because it has a really good compression ratio and because it s fast About the Random Numbers used as Session Keys PGP uses a cryptographically strong pseudo random number generator for creating temporary session keys If this random seed file does not exist it is automatically created and seeded with truly random numbers derived from your random events gathered by the PGP program from the timing of your keystroke and mouse movements This generator reseeds the seed file each time it is used by mixing in new material partially derived from the time of day and other truly random sources It uses the conventional encryption algorithm as an engine for the random number generator The seed file contains both random seed material and random key material used to key the conventional encryption engine for the random generator This random seed file should be protected from disclosure to reduce the risk of an attacker deriving your next or previous session keys The attacker would have a very hard time getting anything useful from capturing this random seed file because the file is cryptographically laundered before and afte
124. ring PGP will not copy the trust information along with the key because your private opinions on trust are regarded as confidential When PGP is calculating the validity of a public key it examines the trust level of all the attached certifying signatures It computes a weighted score of validity e g two marginally trusted signatures are deemed as credible as one fully trusted signature The program s skepticism is adjustable for example you may tune PGP to require two fully trusted signatures or three marginally trusted signatures to judge a key as valid Your own key is axiomatically valid to PGP needing no introducers signature to prove its validity PGP knows which public keys are yours by looking for the corresponding private keys on the private key PGP also assumes you ultimately trust yourself to certify other keys As time goes on you will accumulate keys from other people whom you may want to designate as trusted introducers Everyone else will choose their own trusted introducers And everyone will gradually accumulate and distribute with their key a collection of certifying signatures from other people with the expectation that anyone receiving it will trust at least one or two of the signatures This will cause the emergence of a decentralized fault tolerant web of confidence for all public keys This unique grass roots approach contrasts sharply with standard public key management schemes developed by government or other
125. rivate and certified e mail Key Concepts PGP is based on a widely accepted and highly trusted public key encryption system by which you and other PGP users generate a key pair consisting of a private key and a public key As its name implies only you have access to your private key but in order to correspond with other PGP users you need a copy of their public key and they need a copy of your public key You use your private key to sign the e mail messages and file attachments you send to others and to decrypt the messages and files they send to you Conversely you use the public keys of others to send them encrypted mail and to verify their digital signatures NOTE Without going into too much technical detail you might be interested to know that it is not actually the content of the e mail that is encrypted using the public key encryption scheme Instead the data is encrypted using a much faster single key algorithm and it is this single key that is actually encrypted using the recipients public key The recipient then uses their private key to decrypt this key which allows them to decipher the encrypted data PGP for Personal Privacy Version 5 0 User s Guide for W indows 21 22 Your private key is also used to sign the contents of a given e mail message or file attachment Anyone who has a copy of your public key can check your digital signature to confirm that you are the originator of the mail and that the contents have
126. rsion 5 0 User s Guide for W indows vi System RROHITORITBEITUS iuda dd 8 9r UR d aaea REY RAE dedo Rai 7 Compatibility with Other Versions 0 nn 7 Upgrading from a Previous Version 1 cece n 8 Upgrading from PGP 2 6 2 MIT Freeware cece ees 9 Upgrading from PaPinall 4 0 i55 4459444 44444 644659 0440444044440 08 10 Upargdiig Tom POPE AS 222i uo sed gat Y aca Sede wk da wae wes 10 Upgrading from previous beta versions of PGPmail 5 0 Pags 11 Dr qul A TCPTPPCPPcrr rrr 12 Te Install PGP ioma CD BO ME os ceo seats koe Rr bt Re ERE RR OUR aed i2 Tonsil PIS P from PIS Ps WI Sb SNE i oon sese m dme e Re y Ree RR css 12 RUNING PGP 4 cusacacexope p cbbpbGooobboDD XO REOR RR RR UR CR RR dk Le Using PGP from the System tray B Sao RR Ros TT TP Bi Bowe seres LS Performing PGP functions from the Clipboard 0 0 0 c eee eee eee 13 Opening the PGPkeys Window cee ee 14 beilo Prefere ES a o ses ai dtt a eG aged ie ecd acd ugue dr aU ada 15 etiig Help duecossedeRtAEREEERESU ER eain E KR edd d OR des 15 UNE POP utate d aod qo deu de Eo e acl Oh ec d ee eure 15 Using PGP from Supported E mail Applications ies 16 Using PGP from the Windows Explorer ATTE uns oe Terre Ter l Selecting Reciplents ii sees te assacsk x err hirit ee ire nnna E GA AA 18 Tali SPORUS cpcrennrepireniii ac aE EE CR 18 Chapter 3 Making and Exchanging KeyS i e 21 K EOE dee ee eae ns Goa 21 Hare hee P
127. s Public Ke About the Message Digest The message digest is a compact 160 bit or 128 bit distillate of your message or file checksum You can also think of it as a fingerprint of the message or file The message digest represents your message such that if the message were altered in any way a different message digest would be computed from it This makes it possible to detect any changes made to the message by a forger A message digest is computed using a cryptographically strong one way hash function of the message It should be computationally infeasible for an attacker to devise a substitute message that would produce an identical message digest In that respect a message digest is much better than a checksum because it is easy to devise a different message that would produce the same checksum But like a checksum you can t derive the original message from its message digest The message digest algorithm now used in PGP Version 5 0 and later is called SHA which stands for Secure Hash Algorithm designed by the NSA for National Institute of Standards and Technology NIST SHA is a Chapter 6 Security Features and Vulnerabilities 160 bit hash algorithm Some people might regard anything from the NSA with suspicion because the NSA is in charge of intercepting communications and breaking codes But keep in mind that the NSA has no interest in forging signatures and the government would benefit from a good unforgeable d
128. s menu The Export Key to File dialog box appears Expors Key to File Save in EPGP rl amp e z f bn dl fa bn ib at Enclypt 32 5 fa DelsL1 isu a keydb lib fa DelsL 2 isu 4 KEYMGMI fa DelsL3 isu a keys aexpk aj DelsL4 isu B license tet gt Save as type tf rj Cancel 3 Enter the name of the file where you want the key to be exported and then click Save The exported key is saved to the named file in the specified directory location Revoking a Key If the situation ever arises that you can no longer trust your personal key pair you can issue a revocation to the world telling everyone to stop using your public key The best way to circulate a revoked key is to place it on a public key server To revoke a key l Select the key pair to revoke 2 Choose Revoke from the Keys menu Chapter 5 Managing KeysAnd Setting A message appears with some brief information on the implications of revoking a key and asking you to specify whether you really want to revoke the selected key PGPkeys N You are about to revoke your default signing encryption key You will no longer be able to sign with this key and once distributed others will be unable to encrypt data to this key Are you sure you want to do this 3 Click Yes to confirm your intent to revoke the selected key The Enter Passphrase dialog box appears asking you to enter the pas
129. se from being able to use your private key you should only store it on your own computer If your computer is attached to a network you should also make sure that your files are not automatically included in a system wide backup where others might gain access to your private key Given the ease with which computers are accessible over today s networks if you are working with extremely sensitive information you may want to keep your private key on a floppy disk which you can insert like an old fashioned key whenever you want to read or sign your private mail As another security precaution consider assigning a different name to your private keyring file and then storing it somewhere other than in the default PGP file directory where it will not be so easy to locate You use the Keys pane of the PGPkeys Preferences dialog box to specify a name and location for your private and public key ring files Chapter 3 Making and Exchanging Keys Distributing Your Public Key After you create your keys you need to make them available to others so that they can send you encrypted e mail and verify your digital signature You have several alternatives for distributing your public key Make your public key available through a public key server Include your public key in an e mail message Export your public key or copy it to a text file Since your public key is basically composed of a block of text it is really quite easy to make it availabl
130. se it bears your signature It PGP for Personal Privacy Version 5 0 User s Guide for W indows 97 98 may be ill advised to rely on hearsay don t sign her public key unless you have independent first hand knowledge that it really belongs to her Preferably you should sign it only if you got it directly from her In order to sign a public key you must be far more certain of that key s ownership than if you merely want to use that key to encrypt a message To be convinced of a key s validity enough to use it certifying signatures from trusted introducers should suffice But to sign a key yourself you should require your own independent firsthand knowledge of who owns that key Perhaps you could call the key s owner on the phone and read the key fingerprint to her to confirm that the key you have is really her key and make sure you really are talking to the right person Bear in mind that your signature on a public key certificate does not vouch for the integrity of that person but only vouches for the integrity the ownership of that person s public key You aren t risking your credibility by signing the public key of a sociopath if you are completely confident that the key really belongs to him Other people would accept that key as belonging to him because you signed it assuming they trust you but they wouldn t trust that key s owner Trusting a key is not the same as trusting the key s owner It would be a good idea to keep
131. se that identifies a key pair For example one common format for a User ID is the owner s name and e mail address The User ID helps users both the owner and colleagues identify the owner of the key pair Verification The act of comparing a signature created with a private key to its public key Verification proves that the information was actually sent by the signer and that the message has not been subsequently altered by anyone else PGP for Personal Privacy Version 5 0 User s Guide for W indows 119 120 A Glossary of Terms Index A address adding new email 64 attributes changing your keyrings 58 63 viewing your keyrings 58 63 C certifying authority 96 public keys 3 96 Certifying A uthority 96 Change passphrase property 63 changing passphrases 69 checking authenticity of a key 40 fingerprints 65 checksum 94 Clipboard decrypting via the 53 encrypting via the 46 48 using PGP from 13 verifying via the 53 comparing fingerprints 41 compatibility PGP MIME standard 8 versions of PGP 7 with DSS Diffie Hellman technology 8 Created property 62 creating key pairs 22 private and public key pairs 14 cryptography overview 2 D decrypting email 4 from others 51 overview 2 file attachments 54 from the Clipboard 13 from W indows Explorer 54 54 56 via the Clipboard 53 decryption how it works 21 setting preferences 75 defaults specifying 63 deleting digital signatures 69 keys 69
132. send them mail and also relieves you from having to store a lot of keys on your public key ring Chapter 3 Making and Exchanging Keys There are a number of public key servers such as the one maintained by PGP Inc where you can locate the keys of most PGP users If the recipient has not pointed you to the Web address where their public key is stored you can access any key server and do a search for the user s name or e mail address since all key servers are regularly updated to include the keys stored on all the other servers However with this version of PGP don t have to go through this old fashioned method but can instead quickly locate a specific user s key when you are sending e mail or managing your keys from the PGPkeys window To get someone s public key from a key server 1 Open the PGPkeys window by clicking on the lock and key icon in the Win95 tray or click the Start button and choose PGPkeys from the PGP submenu of the Programs menu 2 Choose Find New Key from the Keyserver submenu of the Keys menu The Find Key dialog box appears Email Address or Key ID NENNEN Cancel 3 Enter the e mail address or user name to locate the users public key If a public key for the specified user is found you are asked whether you want to add it to your public keyring When you add a public key to your keyring the key will show up in the PGPkeys window where you can examine it to make sure that it is valid Adding Pu
133. sphrase PGP Enter Passphrase i2 x Passphrase of selected key v Hide Typing l n 4 Enter your passphrase and then click OK When you revoke a key it is crossed out with a red line to indicate that it is no longer valid 5 Send the revoked key to the server so everyone will know not to use your old key It is possible that you might forget your passphrase someday In that case you would never be able to use your key again and you would have no way of revoking your old key when you create a new one To safeguard against this possibility you can create a revocation key by making a copy of your private key revoking the copy and saving it in a safe place You can then send the revoked copy to a public key server if you ever forget your password However you should be very careful about where you PGP for Personal Privacy Version 5 0 User s Guide for Windows 13 store the revoked version of your key If someone were to get hold of the revoked key they could revoke your key and replace it with one of their own making Setting Your Preferences PGP is configured to accommodate the needs of most users but you have the option of adjusting some of the settings to suit your particular computing environment You specify these settings through the Preferences dialog box which you can access using one of the following methods Click the lock and key icon and choose Preferences Choose Preferences from the Edit menu in the P
134. st level of validity based on the assumption that you will only sign someone s key if you are totally convinced that it is valid The validity of any other keys which you have not personally signed depends on the level of trust you have granted to any other users who have signed the key If there are no signatures associated with the key then it is not considered valid and a message indicating this fact appears whenever you use the key Indicates the level of trust you have granted to the owner of the key to serve as an introducer for the public keys of others This trust comes into play when you are unable to verify the validity of someone s public key for yourself and instead elect to rely on the judgement of other users who have signed the key When you create a set of keys they are considered implicitly trustworthy as represented by the striping in the trust and validity bars When you receive a public key from someone that has been signed by another of the user s keys on your public keyring the level of authenticity is based on the trust you have granted to the signer of that key You assign a level of trust either Complete Marginal or Untrusted in the Properties dialog box PGP for Personal Privacy Version 5 0 User s Guide for W indows 59 Creation Size Shows the date when the key was originally created You can sometimes make an assumption about the validity of a key based on how long it has been in circu lation If
135. t or perhaps more abruptly from the bombing of a Federal building A year after the 1994 Digital Telephony bill passed the FBI disclosed plans to require the phone companies to build into their infrastructure the capacity to simultaneously wiretap one percent of all phone calls in all major US cities This would represent more than a thousandfold increase over previous levels in the number of phones that could be wiretapped In previous years there were only about 1000 court ordered wiretaps in the US per year at the federal state and local levels combined It s hard to see how the government could even employ enough judges to sign enough wiretap orders to wiretap 1 of all our phone calls much less hire enough federal agents to sit and listen to all that traffic in real time The only plausible way of processing that amount of traffic is a massive Orwellian application of automated voice recognition technology to sift through it all searching for interesting keywords or searching for a particular speaker s voice If the government doesn t find the target in the first 1 sample the wiretaps can be shifted over to a different 1 until the target is found or until everyone s phone line has been checked for subversive traffic The FBI says they need this capacity to plan for the future This plan sparked such outrage that it was defeated in Congress at least this time around in 1995 But the mere fact that the FBI even asked for these broad pow
136. t as it was ported to other more complex operating systems such as Microsoft Windows or the Macintosh OS a new vulnerability emerged This vulnerability stems from the fact that these fancier operating systems use a technique called virtual memory Virtual memory allows you to run huge programs on your computer that are bigger than the space available in your computer s semiconductor memory chips This is handy because software has become more and more bloated since graphical user interfaces became the norm and users started running several large applications at the same time The operating system uses the hard disk to store portions of your software that aren t being used at the moment This means that the operating system might without your knowledge write out to disk some things that you thought were kept only in main memory Things like keys passphrases or decrypted plaintext PGP does not keep that kind of sensitive data lying around in memory for longer than necessary but these is some chance that the operating system could write it out to disk anyway The data is written out to some scratchpad area of the disk known as a swap file Data is read back in from the swap file as needed so that only part of your program or data is in physical memory at any one time AII this activity is invisible to the user who just sees the disk chattering away Microsoft Windows swaps chunks of memory called pages using a Least Recently Used LRU pag
137. t data only while it s encrypted direct physical security violations can still compromise plaintext data or written or spoken information This kind of attack is cheaper than cryptanalytic attacks on PGP Tempest Attacks Another kind of attack that has been used by well equipped opponents involves the remote detection of the electromagnetic signals from your computer This expensive and somewhat labor intensive attack is probably still cheaper than direct cryptanalytic attacks An appropriately instrumented van can park near your office and remotely pick up all of your keystrokes and messages displayed on your computer video screen This would compromise all of your passwords messages etc This attack can be thwarted by properly shielding all of your computer equipment and network cabling so that it does not emit these signals This shielding technology is known as Tempest and is used by some government agencies and defense contractors There are hardware vendors who supply Tempest shielding commercially Protecting Against Bogus Timestamps A somewhat obscure vulnerability of PGP involves dishonest users creating bogus timestamps on their own public key certificates and signatures You can skip over this section if you are a casual user and aren t deeply into obscure public key protocols Chapter 6 Security Features and Vulnerabilities There s nothing to stop a dishonest user from altering the date and time setting of his own syst
138. tem tray You can access many of the main PGP functions by clicking the lock and key icon that is normally located in the System tray and then selecting the appropriate menu item If you cannot find this icon in your System tray you need to run PGP from the Start menu Encrypt Clipboard Sign Clipboard Encrypt And Sign Clipboard Decrypt Verify Clipboard Add Key from Clipboard Edit Clipboard Text Launch Associated Viewer Launch PGPkeys PGP Preferences Help Quit PGPtray 10 28 AM Performing PGP functions from the Clipboard You will notice that many of the options on this menu refer to PGP functions that you perform from the Windows clipboard If you are using an e mail application that is not supported by the PGP plug ins or you are working with text generated by some other application you perform your encryption decryption and signature V verification functions via the Windows clipboard For instance to encrypt or sign text you copy it from your application to the clipboard encrypt and sign it using the appropriate PGP functions then paste it back into your application before sending it to the intended recipient s When you receive an encrypted or signed e mail message you simply reverse the process and copy the ciphertext from your application to the clipboard decrypt and verify the information and then view the contents After you view the decrypted message you can decide whether to save the
139. ter to prevent others from accessing them To access PGP functions from the Windows Explorer choose the appropriate option from the PGP submenu of the File menu pen Print Add to Zip Send To gt Encrypt eR z Sign Create Shortcut Delete Rename Properties Close The options that appear depend on the current state of the file you have selected If the file has not yet been encrypted or signed then the options for performing these functions appear on the menu If the file is already encrypted or signed then options for decrypting and verifying the contents of the file are displayed PGP for Personal Privacy Version 5 0 User s Guide for W indows 17 18 Selecting Recipients When you send e mail to someone whose e mail application is supported by the PGP plug ins the recipient s e mail address determines which keys to use when encrypting the contents However if you enter a user name or e mail address that does not correspond to any of the keys on your public keyring or if you are encrypting from the clipboard or the Windows Explorer you must manually select the recipient s public key from the PGP Key Selection Dialog box PGPmail Key Selection Dialog L2 x Drag users from this list to the Recipients list Validit amp Michael lannamico lt mji pap com gt 2048 1024 amp Philip R Zimmermann lt prz acm org gt rc mmm 1024 Validity Tus Size 2048 Michael J lanna
140. transmitted via secure channels so that both parties can know it before encrypted messages can be sent over insecure channels This may be inconvenient If you have a secure channel for exchanging keys then why do you need cryptography in the first place 0101011001001001 Message Encryption Encrypted Message How Public Key Cryptography Works In public key cryptography as shown in Figure 2 everyone has two related complementary keys a public key and a private key Each key unlocks the code that the other key makes Knowing the public key does not help you deduce the corresponding private key The public key can be published and widely disseminated across a communications network This protocol provides privacy without the need for the same kind of secure channels that conventional secret key encryption requires Chapter 6 Security Features and Vulnerabilities Anyone can use a recipient s public key to encrypt a message to that person and that recipient uses her own corresponding private key to decrypt that message No one but the recipient can decrypt it because no one else has access to that private key Not even the person who encrypted the message with the recipient s public key can decrypt it igure Public Key Cryptography Public Key Private Key CLIII Purchase Order Encryption Encrypted Message rypti Messaia How Your Files and Messages are En
141. tware The information in this document is subject to change without notice Pretty Good Privacy Inc does not warrant that the in formation meets you requirements or that the information is free of errors The information may include technical inaccuracies or typographical errors Changes may be made to the information and incorporat ed in new editions of this document if and when made available by Pretty Good Privacy Inc Export of this software and documentation may be subject to compliance with the rules and regulations promulgated from time to time by the Bureau of Export A dministration United States Department of Com merce which restrict the export and re export of certain products and technical data PRETTY GOOD PRIVACY INC 2121 South El Camino Real Suite 902 San Mateo CA 94403 415 631 1747 415 572 1932 fax info pgp com http www pgp com LIMITED WARRANTY Pretty Good Privacy Inc warrants that the Softwarewill perform substantially in ac cordance with the written materials in this package for a period of 90 days from the date of original purchase Pretty Good Privacy Inc s entire liability and your exclusive remedy shall be at Pretty Good Privacy Inc s option either a return of the purchase price paid for the license or b repair or replacement of the Software that does not meet Pretty Good Privacy Inc s limited warranty and which is returned at your expense to Pretty Good Privacy Inc with a copy of
142. uld create notarized signatures with a trustworthy timestamp This would not necessarily require a centralized authority Perhaps any trusted introducer or disinterested party could serve this function the same way real notary publics do now When a notary signs other people s signatures it creates a signature certificate of a signature certificate This would serve as a witness to the signature the same way real notaries now witness handwritten signatures The notary could enter the detached signature certificate without the actual whole document that was signed into a special log controlled by the notary Anyone can read this log The notary s signature would have a trusted timestamp which might have greater credibility or more legal significance than the timestamp in the original signature PGP for Personal Privacy Version 5 0 User s Guide for W indows 113 114 There is a good treatment of this topic in Denning s 1983 article in IEEE Computer see the Recommended Introductory Readings section below Future enhancements to PGP might have features to easily manage notarized signatures of signatures with trusted timestamps Exposure on Multi user Systems PGP was originally designed for a single user PC under your direct physical control If you run PGP at home on your own PC your encrypted files are generally safe unless someone breaks into your house steals your PC and convinces you to give them your passphrase or your passphrase
143. ur RSA key by using some new secret factoring breakthrough But civilian academia has been intensively attacking it without success since 1978 Chapter 6 Security Features and Vulnerabilities Perhaps the government has some classified methods of cracking the IDEA conventional encryption algorithm used in PGP This is every cryptographer s worst nightmare There can be no absolute security guarantees in practical cryptographic implementations Still some optimism seems justified The IDEA algorithm s designers are among the best cryptographers in Europe It has had extensive security analysis and peer review from some of the best cryptanalysts in the unclassified world It appears to have some design advantages over DES in withstanding differential cryptanalysis Besides even if this algorithm has some subtle unknown weaknesses PGP compresses the plaintext before encryption which should greatly reduce those weaknesses The computational workload to crack it is likely to be much more expensive than the value of the message If your situation justifies worrying about very formidable attacks of this caliber then perhaps you should contact a data security consultant for some customized data security approaches tailored to your special needs In summary without good cryptographic protection of your data communications it may have been practically effortless and perhaps even routine for an opponent to intercept your messages especially thos
144. ur public key to a key server 1 Open the PGPkeys window by clicking on the lock and key icon in the Win95 tray or click the Start button and choose PGPkeys from the PGP submenu of the Programs menu 2 Select the icon that represents the public key you want to post on the key server 3 Choose Send Selected Keys from the Keyserver submenu of the Keys menu As an alternative you can click the right mouse button and select this option from the pop up menu After placing a copy of your public key on a key server you can tell those who want to send you encrypted mail or verify your digital signature to get a copy of your key from the server Even if you don t explicitly point someone to your public key they can get a copy by searching the key server for your name or e mail address Many people include the Web address for their public key in the footer of their of their e mail messages in many cases the recipient can just double click the address to access a copy of your key on the server If you ever need to change your e mail address or you acquire new signatures all you have to do to replace you old key is send a new copy to the server and the information is automatically updated However you should keep in mind that public key servers are only capable of updating new information and will not be updated to reflect user names or signatures which have been removed from your key If your key is ever compromised you can revoke your key whic
145. ver your data has been compromised Sometimes commercial packages use the Federal Data Encryption Standard DES a fairly good conventional algorithm recommended by the government for commercial use but not for classified information PGP for Personal Privacy Version 5 0 User s Guide for W indows 103 104 oddly enough Hmmm There are several modes of operation DES can use some of them better than others The government specifically recommends not using the weakest simplest mode for messages the Electronic Codebook ECB mode But they do recommend the stronger and more complex Cipher Feedback CFB or Cipher Block Chaining CBC modes Unfortunately most of the commercial encryption packages I ve looked at use ECB mode When I ve talked to the authors of a number of these implementations they say they ve never heard of CBC or CFB modes and didn t know anything about the weaknesses of ECB mode The very fact that they haven t even learned enough cryptography to know these elementary concepts is not reassuring And they sometimes manage their DES Keys in inappropriate or insecure ways Also these same software packages often include a second faster encryption algorithm that can be used instead of the slower DES The author of the package often thinks his proprietary faster algorithm is as secure as DES but after questioning him I usually discover that it s just a variation of my own brilliant scheme from college days Or maybe he
146. y clicking a button when sending or receiving your e mail If you are using an email application that is not supported by the plug ins you can easily transfer the text of your email messages to the clipboard and perform the necessary functions from there In addition if you need to encrypt or decrypt entire file attachments you can do so directly from the Windows Explorer by choosing the appropriate menu option Here are some of the features offered by PGP e Widely trusted encryption and decryption incorporating maximum strength cryptographic technologies Digital signature and verification for certifying messages and files Quick access to all functions from easily selectable menu items PGP for Personal Privacy Version 5 0 User s Guide for W indows Integrated plug in support for popular email applications Implementation of PGP MIME for quick encryption and decryption of messages and file attachments when sending and receiving email e Simple key generations with up to 4096 bit keys and support for multiple key formats RSA and DSS Diffie Hellman e Sophisticated key management with graphical representations of key properties Integrated support for distributing and retrieving keys from public key servers NOTE Ifyou are running the DSS Diffie Hellman version of PGP for Personal Privacy it does not generate keys using the RSA algorithm nor does it encrypt decrypt sign or verify using RSA keys If you find
147. you want to sign with click the down arrow and select the desired key 5 Once you have signed someone s public key a quill icon associated with your user name is shown for that key Granting Trust for Key Validations Besides certifying that a key belongs to someone you can assign a level of trust to the user of the keys indicating how well you trust them to act as an introducer to others whose keys you may get in the future This means that if you ever get a key from someone that has been signed by an individual that you have designated as trustworthy the key is considered valid even though you have not done the check yourself To grant trust for a key l Select the key for which you want to change the trust level 2 Choose Key Properties from the Keys menu PGP for Personal Privacy Version 5 0 User s Guide for W indows 67 68 The Properties dialog box appears test lt mji aol com gt 24 x General KepID 0x52163581 Created 5 1 97 Key Type RSS Expires Never Trust Model Validity Invalid Invalid Valid Untusted Trusted Trust Untrusted Es r Eingerprint 9355 7D36 3DF8 467E 7C43 688E 0780 7834 v Enabled Cancel Help 3 Use the trust level sliding bar to choose the appropriate level of trust for the key You have a choice of Untrusted Marginal or Complete 4 Click OK to accept the new setting Disabling and Enabling Keys Sometimes you may want to temporarily
148. your own public key on hand with a collection of certifying signatures attached from a variety of introducers in the hopes that most people will trust at least one of the introducers who vouch for the validity of your public key You could post your key with its attached collection of certifying signatures on various electronic bulletin boards If you sign someone else s public key return it to them with your signature so that they can add it to their own collection of credentials for their own public key PGP Keeps track of which keys on your public keyring are properly certified with signatures from introducers that you trust All you have to do is tell PGP which people you trust as introducers and certify their keys yourself with your own ultimately trusted key PGP can take it from there automatically validating any other keys that have been signed by your designated introducers And of course you can directly sign more keys yourself Make sure that no one else can tamper with your own public keyring Checking a newly signed public key certificate must ultimately depend on the integrity of the trusted public keys that are already on your own public keyring Maintain physical control of your public keyring Chapter 6 Security Features and Vulnerabilities preferably on your own personal computer rather than on a remote timesharing system just as you would do for your private key This is to protect it from tampering not from disclosure
149. your receipt This limited warranty is void if failure of the Software has re sulted from accident abuse or misapplication Any repaired or replacement Software will be warranted for the remainder of the original warranty period or 30 days whichever is longer IF THE SOFTWARE IS EXPORT CONTROLLED SEE BELOW THESE REMEDIES ARE NOT AVAIL ABLE OUTSIDE THE UNITED STATES OF AMERICA NO OTHER WARRANTIES EXCEPT FOR THE WARRANTIES SET FORTH HEREIN THE SOFTWARE AND DOCUMENTATION ARE PROVIDED AS IS AND PRETTY GOOD PRIVACY INC DISCLAIMS ALL OTHER WARRANTIES EITHER EXPRESS OR IM PLIED INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY FITNESS FOR A PARTICULAR PURPOSE CONFORMANCE WITH DESCRIPTION AND NON INFRINGEMENT OF THIRD PARTY RIGHTS THIS LIMITED WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS YOU MAY HAVE OTHERS WHICH VARY FROM STATE TO STATE LIMITATION OF LIABILITY PRETTY GOOD PRIVACY INC S CUMULATIVE LIABILITY TO YOU OR ANY OTHER PARTY FOR ANY LOSS OR DAMAGES RESULTING FROM ANY CLAIMS DEMANDS OR ACTIONS ARISING OUT OF OR RELATING TO THIS AGREEMENT SHALL NOT EXCEED THE PURCHASE PRICE PAID FOR THE LICENSE IN NO EVENT SHALL PRETTY GOOD PRIVACY INC OR ITS SUPPLIERS BE LIABLE FOR ANY INDIRECT IN CIDENTAL CONSEQUENTIAL SPECIAL OR EXEMPLARY DAMAGES OR LOST PROFITS WHATSOEV ER INCLUDING WITHOUT LIMITATION DAMAGES FOR LOSS OF BUSINESS PROFITS BUSINESS INTERRUPTION LOSS OF BUSINESS INFORMATION OR OTHER PECUNIARY LOSS ARIS
150. yptand sign from the Windows Explorer ccc cee eee 48 Decrgp ng and Verifying E mall cic cede ted Y Y 90 RO eo 51 Decrypting and Verifying from Supported e mail Applications 51 To decrypt and verify with supported e mail applications 00eu 52 Decrypting and Verifying Via the Clipboard see 53 To decrypt and verify using the clipboard 1 cece cee eee ees 53 Decrypting and Verifying from the Windows Explorer 0 cee u eee eas 54 To decrypt and verify from the Windows Explorer cee eevee une 54 PGP for Personal Privacy Version 5 0 User s Guide for W indows vii Chapter 5 Managing Keys And Setting Preferences isses 57 LENCMUIDUEOGNETX PPP PTTTTPT R 57 The PGPkeys Window TETE ETETE TET eee were TUE shih Sistas PG Pkeys Attribute Definitions ccc eee es TTD 59 PPkeys kon Ben mtis 1nucoussd kde eee lb goce d iR Ek Ange ee duse 60 Examining a Key s Properties bd Gerais odii ere Pip ds vy dg Specihung a Dersulb Roy Pall cc cece xd pp eee E UE CES E HERER P E Er 63 To specify your default key pair liess 64 Adding a New User Name or Address T TT kor oon hd 64 To add a new user name or address to an existing key ccc eee 64 Checking d Key S FIBBEIDHBE eb apes se OG ESE ESSE EERE LEGS OLE E RE 65 Te checka Kees NOEP uoa eacus abo qid iG eq d RR aden 65 Signing Someone s Public KBy scsskessc rat RR RR
151. ypting from 48 50 signing from 48 50 verifying from 54 56 worm 110 Index PG P for Personal Privacy Version 5 0 User s Guide for Windows 127 128 Index

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Pretty Good Privacy™ PGP for Personal Privacy, Version 5.0