Section: 6.8.1.5 USIM
Content: The USIM shall support UMTS AKA and may support backwards compatibility with the GSM system, which consists of: Feature 1: 64-bit GSM cipher key derivation (conversion function c3) to access GSM BSS attached to a R99+ VLR/SGSN using a dual-mode R99+ ME; Feature 2: GSM AKA to access the GSM BSS attached to a R98- VLR/SGSN or when using ME not capable of UMTS AKA; Feature 3: SIM-ME interface (GSM 11.11) to operate within ME not capable of UMTS AKA. When the ME provides the USIM with RAND and AUTN, UMTS AKA shall be executed. If the verification of AUTN is successful, the USIM shall respond to the ME with the UMTS user response RES and the UMTS cipher/integrity keys CK and IK. The ME shall store CK and IK as current security context data on the USIM. If the USIM supports access to 64-bit GSM cipher key derivation (feature 1), the USIM shall also derive the 64-bit GSM cipher key Kc from the UMTS cipher/integrity keys CK and IK using conversion function c3 and send the derived Kc to the ME. In case the verification of AUTN is not successful, the USIM shall respond with an appropriate error indication to the ME. When the ME provides the USIM with only , and the USIM supports GSM AKA (Feature 2), GSM AKA shall be executed. The USIM first computes the UMTS user response RES and the UMTS cipher/integrity keys CK and IK. The USIM then derives the GSM user response SRES and the 64-bit GSM cipher key Kc using the conversion functions c2 and c3 and send the GSM user response SRES and the 64-bit GSM cipher key Kc to the ME. The ME shall store the 64-bit GSM cipher key Kc as the current security context on the USIM. In case the USIM does not support 64-bit GSM cipher key derivation (Feature 1) or GSM AKA (Feature 2), the ME shall be informed. An ME with a USIM that does not support GSM cipher key derivation (Feature 1) shall not perform the GSM cipher key derivation (conversion function c3) in the ME and therefore cannot operate in any GSM BSS with 64-bit key ciphering enabled. An ME with a USIM that does not support GSM AKA (Feature 2) cannot operate under a R98- VLR/SGSN. A USIM that does not support GSM AKA (Feature 2) cannot work within a ME that is not capable of UMTS AKA.