AN510: Adding Security to EnOcean Receivers: NOTES FOR
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1. Code MSB Most Significant Byte PSK Pre shared Key PTM Pushbutton Transmitter Module RLC Rolling Code R ORG Message parameter identifying the message type SLF Security Level Format specifying which security parameters are used TXID ID of a transmitter VAES Variable AES 1 2 References 1 Security of EnOcean radio networks System Specification http www enocean com en security specification 2 http www kotfu net 2011 08 what does it take to hack aes 3 EEP Specification http www enocean alliance org eep 4 GP Specification http www enocean alliance org 5 EnOcean Radio Protocol 1 http www enocean com fileadmin redaktion pdf tec_docs EnOceanRadioProtocol pdf EnOcean www enocean com Marian H nsch September 2015 Page 3 12 APPLICATION NOTE 510 Green Smart Wireless enocean 6 Smart Acknowledge http www enocean com fileadmin redaktion pdf tec_docs SmartAcknowledgement pdf 7 Remote Management http www enocean com fileadmin redaktion pdf tec_docs RemoteManagement pdf 8 Gateway Controller http www enocean com en enocean software gateway controller 9 Dolphin V4 Gateway Controller http www enocean com en enocean software 10 EnOcean Link http www enocean com en enocean software enocean link 11 EnOcean Link Gateway example http www enocean com fileadmin redaktion support enocean link gateway exa2. of storing the RLC must be chosen The RLC is typically 2 or 3 bytes long but only one byte is changing therefore we do only a pre calculation based on the assumption that only one byte is written per write cycle With this byte an index of the device is written too Together two bytes are written Storing Rolling Code every 30 received Telegram 128 2 30 20 000 24 6 400 000 Telegrams per Device minimum the en durance can be much higher STM330 sends 96 Telegrams per day 6 400 000 96 187 years of operation Note By choosing a more effective RLC storage strategy this number can be in creased or optimized for a specific use case Please consider that erase operations require 20ms and 20 mA of current It is cru cial that the device does not lose power during a flash erase operation It has been reported that other pages can also be damaged in this case Please ensure that your device does not lose power during erase operations e g connect a capacitator as an energy buffer Consider turning off the radio during erase operations to lower the overall energy consumption Having a storing cycle higher than the rolling code window is not recommended If an unplanned power down of the receiver will occur then at power up the receiver will recover the last stored RLC The recovered RLC can be far less than the actual RLC of the transmitter If the storing cycle is bigger than the RLC window itself then the receiver and trans
3. 0 C U It can also be flashed to TCM 300 C U Dolphin V4 Gateway Controller The default firmware for TCM410 J and USB 400 In this case the security features are implemented on the external uC The EnOcean trans parent gateway forwards all messages unchanged to the uC Security features only affect the message payload which is not changed by the translation from the enocean radio to the enocean serial protocol Therefore a seamless bidirectional translation between radio and serial protocol including security features is also possible If a message is encrypted the encryption will remain when it has been translated from a radio to a serial message For illustration of this please see Figure 3 APPLICATION NOTE 510 Green Smart Wireless enocean 0X21 0x25 0x48 0x44 EnOcean Serial Protocol pe coan Madig 1 0 iE Wi re 1 SO IEC Al r T UART Signal Radio Signal Figure 3 Seamless translation between serial and radio protocol ISO IEC 14543 3 10 The pprocessing of security features is also possible in an external controller The next two chapters focus on their implementation 3 1 1 Using EnOcean Link EnOcean Link is middleware for the EnOcean Protocol stack It is a library delivered along with source code Its features provide and handle all tasks required to embed EnOcean into an application By embedding EnOcean Link on a HC you gain a very powerful tool which handles the processing of the en
4. APPLICATION NOTE 510 SECURITY IN RECEIVERS Green Smart Wireless enocean APPLICATION NOTE 510 Green Smart Wireless enocean Table of contents 1 2 3 INTRODUCTION 6essssisicesisssscecsssssdeasssacsacscccaceassacsseassscascasssasssasssaasaasscasssasssaaiaassiasssasssacisasasasisasasaniiasasaasiaees 3 1 1 TERINITIONS 5053 56 a Se tc cx nu gels cia hea 20 14 be 05 0 ia he tzce nu geslae lee ade 04 he ae sia betace ou E gesaevtegedace once 3 1 2 IREFERENGES SS E ie 5c face sagas oo 054 400 sige ta oie ge Saco od gas en Se a gsi a 04 eva ge Hace od gals SS SE hea asia ts ev iage Gace sd gens E 3 1 3 REVISION HISTORY mmmmimimi minie mm 4 SECURE LINE POWERED END DEVICEG cccccssssssssssssssssssssssssscssssscssssscssscccccccccscccscscecscscssessees 5 2 1 COMMON TASKS OF A SECURE LINE POWERED DEVICE ccccccccscccsccececccccccecceccccceceeeceeeeeeeeeeeceeeeeeeeeeeeeeeess 7 IMPLEMENTATION OF SECURITY IN LINE POWERED DEVICES 0000000000000000000000000000000000 8 3 1 SECURE APPLICATION WITH TRANSPARENT GATEWAY ccssssessseeseseesseseseeessesseeesesesesesssesesesssssessseeesenes 8 Ill Using EnOcean Link niecne n eee sa aea aE E e Er eee nee ehe 9 3 1 2 Implementing own security solution and functions uueseesseeessnssenesensenssennnenennnnnnsnnnnannennnnnnennennnen 10 3 2 SECURE APPLICATION WITH DECODING CONTROLLER uueessssssesssnennnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnen
5. ams may be trans lated or tunnelled by a different protocol For example a protocol gateway 1 illustrates the different application types with security TCM 310 C U or TCM 410 with an external CPU running EnOcean Link TCM 310 C U or TCM 410 with and external CPU and security functions imple mented by the customer TCM 315 with external CPU TCM 415 with external CPU A stand alone EnOcean Module with security features implemented using the Dol phin API by a customer In this application note it will be demonstrated how security features are implemented in each of these use cases APPLICATION NOTE 510 Green Smart Wireless enocean EnOcean Software Customer Application Security processing here Dolphin API used by customer K Security functions embedded by customer Figure 1 Security in receiver applications Line powered devices are considered to have unlimited energy and large computing capa bilities In the most common scenario there are many energy autarkic devices Sensors but only one or two line powered devices actuators Therefore line powered devices are designed to be able to receive and process telegrams from more than one device at once The receiver has to know the security parameters of all the devices that send telegrams to it These are the security level format SLF security key KEY and rolling code RLC This information combined builds a security profile The s
6. ecurity profile of every incoming de vice must be stored APPLICATION NOTE 510 Green Smart Wireless enocean 2 1 Common tasks of a secure line powered device In this chapter the additional tasks of a secure device compared to a non secure device are discussed These are as follows Store and maintain security profiles This means that the device needs non volatile memory with a large number of write cycles as the RLC will change frequently The alternative is not to store every change of the RLC but only every 30th or 50th for example This will reduce the number of write cycles enabling memories with lower endurance to be used On the other hand it can result in application instability If the device loses power unexpect edly it can lose synchronisation with the RLCs of the incoming devices Process Security teach In messages Most actuators or Smart Home boxes have a Teach In mode This mode is used to logically link sensors and actuators If a receiver supports security this teach in pro cess must be extended to accept and process secure teach in telegrams Devices which do not have a teach in mode must incorporate security teach in processing in the backbone or somewhere else in the system architecture Process telegrams with security features The essential task of a receiver is to be able to apply the defined security features The security features supported by a device can vary The definition of what s
7. ennnnnnnsnnnnnnnnnenn 10 3 3 CUSTOM SECURITY SOLUTION ON ENOC NO SECURE TRANSMISSION EAN MODULES WITH DOLPHIN API 11 gt APPLICATION NOTE 510 Green Smart Wireless enocean NOTES FOR SECURITY IN DIFFERENT RECEIVER APPLICATION 1 INTRODUCTION This document describes how to add security to line powered applications primarily gate ways and actuators Before reading this document you should be familiar with the specification Security of EnOcean Radio Networks 1 You can also find a good summary of this in application note 509 1 1 Definitions Term Abbr Description HC Microcontroller external AES Advanced Encryption Standard API Application Programming Interface APP Application ASK Amplitude Shift Keying CBC Cipher Block Chaining CMAC Cipher Based Message Authentication Code CRC Cyclic Redundancy Codes DATA Payload of a radio telegram Device Customer end device with an integrated EnOcean radio module EEP EnOcean Eguipment Profile EHW Energy Harvested Wireless protocol ERP EnOcean Radio Protocol ERP1 Version 1 ERP2 Version 2 ESP3 EnOcean Serial Protocol V3 FSK Frequency Shift Keying Gateway Module with a bidirectional serial communication connected to a HOST GP Generic Profiles ID Unique module identification number KEY Specific parameter used to encrypt decrypt transform DATA MAC Message Authentication
8. it is described how the tasks discussed in chapter 2 1 can be implemented for each scenario shown in Figure 1 In general security functionality can be implemented u In EnOcean Modules For small applications with dedicated long term use cases e g HVAC control In external uCs for applications in dynamic environments e g smart home When deciding where to implement the security functionality one has to also consider the computing effort required to perform the security features For example on the EnOcean Dolphin Platform with Dolphin API one ASE128 computing cycle takes 0 25 1ms In this case with a rolling code window of 100 the validation of a message can take in worst case 25 100ms Other external CPUs may have better performance so please also consider how this process is implemented 3 1 Secure application with transparent gateway This application scenario consists of an EnOcean Gateway and an external controller The typical use cases are for example set up boxes TVs and Smart Home boxes The EnOcean Gateway is a transparent modem which forwards all telegrams received without any change to the serial interface and sends out all serial requests to the radio interface This use case is shown in Figure 2 HC ie ARMv7 Figure 2 Security with transparent gateway For the EnOcean transparent gateway you can use for example Gateway Controller Firmware 8 The default firmware for TCM 310 C U and USB 30
9. mitter may become desynchronised even if the device pow ered up immediately after losing power This will result in repeated resynchronisa tion which requires in most cases some action from the user Choose the RLC win dow and storage window carefully Disclaimer The information provided in this document describes typical features of the EnOcean radio system and should not be misunderstood as specified operating characteristics No liability is assumed for errors and or omissions We reserve the right to make changes without prior notice For the latest documentation visit the EnOcean website at www enocean com
10. mple 8cpp example html 12 Decoding Gateway http www enocean com en enocean software decoding gateway controller 13 DolphinAPI http www enocean com en download 14 http www enocean com en enocean software 1 3 Revision History No Major Changes 1 0 First version 1 1 Language Corrections APPLICATION NOTE 510 Green Smart Wireless enocean 2 SECURE LINE POWERED END DEVICES When we consider line powered applications we traditionally refer to them as receivers This convention is based on the very basic use case of a sensor sending data to an actuator But over time the features of EnOcean networks and devices have expanded so that today most line powered devices are actually transceivers This document focuses on security features in line powered devices also taking bidirectional communication in to considera tion A receiver application can consist of one or more processing units The most common re ceiving applications are Figure Ei Stand alone units the EnOcean module handles all application tasks For example an HVAC actuator Dual processing units the EnOcean Module is used as a transparent gateway and there is an external CPU which implements all application relevant functions For ex ample a Smart Home box Distributed Systems the EnOcean Module is also used as a transparent gateway but the external CPU only forwards the telegram further The telegr
11. n implement the security features your self This means that you have to implement all features described in the specification 1 on your uC The following must be implemented E AES 128 encryption and decryption algorithm VAES encryption and decryption AES CBC encryption and decryption CMAC validation Secure teach in processing The storage of security profiles SLC RLC and KEYs The VEAS CMAC and AES CBC tasks require a common AES 128 implementation Depend ing on microcontroller platform and development environment it may be possible find a reference implementation or source code on the Internet 3 2 Secure application with decoding controller This application also consists of an EnOcean Gateway and an external uC but compared to the use case in 0 the EnOcean Gateway handles the security tasks The typical use cases are dedicated actuators and controllers such as light actuators or HVAC controllers Here it is assumed that the external uC has comparable computing capacities and features as the EnOcean module Otherwise it may make more sense to implement the security functions into the external uC Please see visualization of this case in Figure 5 HC ie Atmel 32 bit PTM only HC ie Atmel 32 APPLICATION NOTE 510 Green Smart Wireless enocean Figure 5 Security with decoding gateway In this application the HC only controls the learn mode of the decoding gateway Storage of the security pr
12. ofiles and all security tasks are handled in the decoding gateway It is rec ommended to connect an external EEPROM through CC to the decoding gateway to store the security profiles outside of the EnOcean module You can find as more detailed description of this in the User Manual of the decoding Gate way 12 The TCM 315 is currently capable to decode only PTM 210 telegrams for feature requests please contact us support enocean com The TCM 415 is capable of bidirec tional communication and processing of all possible security features 3 3 Custom security solution on EnOcean Modules with Dolphin API This application is constrained in resources and features compared to applications in chap ter 3 2 and 3 3 but it can still offer a valid baseline for many small or specific applications In general here all aspects of security implementation as described in chapter 3 1 2 must be considered but without the actual security functionality implementation These tasks are handled by the DolphinAPI The DolphinAPI offers these security implementation functions sec_convertToNonsecure SeeBeonver loseeurze sec _createTeachIn sec parseTeachIn For details and usage please refer to the Dolphin API user manual 13 There you can find examples and implementation references The following tasks remain The storage of security profiles SLC RLC and KEYs Implementation of application logic For the storage of security profiles we rec
13. ommend the use of external memory e g EEPROM A receiver must be able to update and store the RLC of all incoming devices Storage of every change of every RLC requires memory which can endure a high number of write cycles The number of write cycles can be reduced by only storing every 30 or 50 change of the RLC and allows memories with lower endurance to be used E g The RLCs may be stored in the flash memory of the Dolphin chip Please consider the example application using a receiver only no secure transmission and storing RLCs in Dolphin Module flash memory Datasheet Dolphin Flash Page 20 000 Erase cycles per page minimum specified endurance E Flash page size 256 bytes E Erasing current typ 20 mA E Erasing time typ 20 ms APPLICATION NOTE 510 Green Smart Wireless enocean Storing keys 2 flash pages to store keys and Device IDs A key is 16 bytes and a device ID is 4 bytes long Total 20 bytes each 2 256 20 24 possible keys devices Storing Rolling Code 2 flash pages for storage of the rolling code 128 writes of a rolling code and index can be written before erasing one page one byte of RLC stored one byte index Note A page can have up 256 write operations before an erase is required But the same byte of a flash page cannot be written twice without first erasing the whole page Rewriting a byte which was already written will result in a failure Here a suitable strategy
14. pecific features a transmitting device uses is defined in the SLF format during the secure teach in process 1 A receiver should support all security features to be interoper able An exception to this can be made for receivers with predefined communication partners which do not use all security features Transmit secure teach in and data telegrams This task is required for secure bidirectional communication To establish a bidirec tional secure link both devices need to send a secure teach in and thus manage each other s security profile A line powered device needs a separate security profile for every outgoing secure communication Resynchronisation A receiver must have the possibility to resynchronize itself with the rolling code of incoming devices For example if a receiver is powered down for a long time but the transmitter continues transmitting and incrementing its RLC the devices may become unsynchronised At start up the receiver will load the last stored RLC but the RLC transmitted may have been incremented outside of the RLC window In this case the devices need to be resynchronized Please see details on resynchronisation in the specification 1 A loss of synchronization may also be caused if the transmit ter is out of range of the receiver or ifthe channel becomes blocked APPLICATION NOTE 510 Green Smart Wireless enocean 3 IMPLEMENTATION OF SECURITY IN LINE POWERED DEVICES In this chapter
15. tire EnOcean protocol stack including the security fea tures For further EnOcean Link information please see reference 10 For the use case visualization with an EnOcean transparent gateway please see Figure 4 Figure 4 A Security implementation with EnOcean Link and an EnOcean gateway Security is an essential part of EnOcean Link By embedding EnOcean Link you will auto matically receive all security functionality for both unidirectional and bidirectional communi cation There are no additional tasks required EnOcean link will also handle all tasks re garding storage and updating of RLCs see Class eoDevice 11 An example can be re viewed in the EnOcean Link user manual for this see Gateway example 11 The security teach in process and profile teach in process are separate actions separate telegrams The EoLink function gateway Receive will return the flag APPLICATION NOTE 510 Green Smart Wireless enocean RECV_SECTEACHIN when a security teach in message is received and the flag RECV_PROFILE when a profile teach in is received The application does not have to per form any explicit action at security teach in For details on the returned flag information please see links 11 and 10 For the use case of a transparent gateway and external HC we recommend using EnOcean Link as the best solution 3 1 2 Implementing own security solution and functions If the use of EnOcean Link is not applicable you ca
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