Security Association / Security Context Bruno Saba DCT/TV/IN 03/05/2010

Space Data Link Secure Protocol Simulator CNES DCT/TV/IN B. Saba 14/04/ Security Association ■Defines cryptographic communication parameters to be used by both the sending and receiving ends of a Secure Channel ■Secure Channel =  One or more Global Virtual Channels (TM and AOS)  One or more Global VC/MAP (TC) ■SA uniquely identified by the Security Parameter Index (SPI) over a defined physical channel. The SPI is transmitted in each frame ■Up to 254 simultaneous SA per physical channel ■Each SA defines a cryptographic service :  Authentication Only (AO)  Encryption Only (EO)  Authenticated Encryption (AE) ■At least one cryptographic key associated to each SA ■SA can be pre-loaded prior to the launch, or dynamically created (mission dependant)

Space Data Link Secure Protocol Simulator CNES DCT/TV/IN B. Saba 14/04/ Security Context ■Defines cryptographic communication parameters to be used by both the sending and receiving ends of a Secure Channel ■Secure Channel =  One or more Global Virtual Channels (TM and AOS)  One or more Global VC/MAP (TC) ■SC uniquely identified by the Security Context Index (SCI) over a defined master channel. The SCI is transmitted in each frame ■Up to 255 simultaneous SC per master channel ■Each SC defines a cryptographic service :  Clear Mode  Authentication Only (AO)  Encryption Only (EO)  Authenticated Encryption (AE) ■No cryptographic key associated to the SC ■Key index transmitted in plaintext in the Security Header ■SC are pre-loaded prior to the launch, NOT dynamically created

Space Data Link Secure Protocol Simulator CNES DCT/TV/IN B. Saba 14/04/ Main Differences between SA / SC ■Security Associations can be dynamically created, Security Contexts are only pre-loaded before flight and can not be changed in flight  For SA, this is a mission dependant feature   If SA are pre-loaded before launch and not modified on flight, then no difference between SA and SC on this point ■Key management  Key directly associated with each Security Association  Key index transmitted in clear mode with Security Context concept  Max 254 pre-loaded keys with Security Association concept  Much more (K index length dependant) when using Security Context concept   If 254 pre-loaded keys is an acceptable limit, then no difference between SA and SC on this point  In each case, key management is to be defined (key revocation, key uploading, key activation, etc.)

Space Data Link Secure Protocol Simulator CNES DCT/TV/IN B. Saba 14/04/ Conclusion ■The main difference is in the key management  Key index transmitted in Security Header when using Security Context Concept  No key index transmitted when using Security Association concept  Less pre-loaded keys with Security Association concept  Max 254 pre-loaded keys when using SA  More key changes during satellite lifetime  Need to maintain a key change log file for deciphering old raw TM data  As the same SPI will be reused with different keys during satellite lifetime

Space Data Link Secure Protocol Simulator CNES DCT/TV/IN B. Saba 14/04/ Proposition ■Amend the proposed SDLS protocol standard  Add an additional attribute to SA : transmission of key index in-line or not. In this case, key index is no more an SA attribute  if key index transmitted in-line, add an additional field in security HDR (16-bit)