security association / security context bruno saba dct/tv/in 03/05/2010

Security Association / Security Context

Bruno Saba

DCT/TV/IN

03/05/2010

Space Data Link Secure Protocol Simulator CNES DCT/TV/IN B. Saba 14/04/2010 2

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)


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


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.)


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


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)

security association / security context bruno saba dct/tv/in 03/05/2010

Documents