Section: 6.8.9.2 GSM security context
Content: A GSM security context is only established for GSM subscribers. At the network side, two cases are distinguished: a) In case of a PS intra SGSN handover the SGSN derives UMTS cipher/integrity keys CK and IK from the 64-bit GSM cipher key Kc (using the conversion functions c4 and c5) agreed during the latest GSM AKA procedure and sends them to the target RNC or BSC. b) In case of a PS Inter SGSN handover the initial SGSN sends the 64-bit GSM cipher key Kc agreed during the latest GSM AKA procedure to the new SGSN controlling the target RNC or BSC. The new SGSN becomes the new anchor point for the service. The new SGSN stores the 64-bit GSM cipher key Kc and derives the UMTS cipher/integrity keys CK and IK which are then forwarded to the target RNC or BSC. At the user side, in all cases, the ME derives the UMTS cipher/integrity keys CK and IK from the 64-bit GSM cipher key Kc (using the conversion functions c4 and c5) received from the SIM during the latest GSM AKA procedure and applies them.