Section: 6.8.1.3 R99+ VLR/SGSN
Content: The AKA procedure will depend on the terminal capabilities, as follows: UMTS subscriber with R99+ ME When the user has R99+ ME, the VLR/SGSN shall send the ME a UMTS authentication challenge (i.e. RAND and AUTN) using a quintet that is either: a) retrieved from the local database, b) provided by the HLR/AuC, or c) provided by the previously visited R99+ VLR/SGSN. Note: Originally all quintets are provided by the HLR/AuC. When the ME is capable of the USIM-ME interface, then UMTS AKA is performed and the VLR/SGSN receives the UMTS response RES. UMTS AKA results in the establishment of a UMTS security context; the UMTS cipher/integrity keys CK and IK and the key set identifier KSI are stored in theVLR/SGSN. When the user is attached to a UTRAN, the UMTS cipher/integrity keys are sent to the RNC, where the cipher/integrity algorithms are allocated. When the user is attached to a GSM BSS, UMTS AKA is followed by the derivation of the GSM cipher keys Kc (and Kc128 when needed)from the UMTS cipher/integrity keys. When the user receives service from an MSC/VLR, the derived cipher keys Kc (and Kc128 when needed) are then sent to the BSC (and forwarded to the BTS). When the user receives service from an SGSN, the derived cipher key Kc or Kc128 applied in the SGSN itself. UMTS authentication and key freshness is always provided to UMTS subscribers with R99+ ME independently of the radio access network. When the ME is not capable of the USIM-ME interface, then GSM AKA is performed and the VLR/SGSN receives the GSM response SRES. GSM AKA results in the establishment of a GSM security context; the 64-bit GSM cipher key Kc and the cipher key sequence number CKSN are stored in the VLR/SGSN. The R99+ VLR/SGSN shall reject authentication if SRES is received in response of a UMTS challenge (RAND, AUTN) over an Iu-Interface. The R99+ VLR/SGSN shall accept authentication if a valid SRES is received in response of a UMTS challenge (RAND, AUTN) over A or Gb-Interface. This will happen in case a UICC is inserted in a ME that is not capable of UMTS AKA and is attached to a GSM BSS. In this case the R99+ VLR/SGSN uses function c2 to convert RES (from the quintet) to SRES to verify the received SRES. UMTS subscriber with R98- ME When the user has R98- ME, the R99+ VLR/SGSN sends the ME a GSM authentication challenge using a triplet that is either: a) derived by means of the conversion functions c2 and c3 in the R99+ VLR/SGSN from a quintet that is: i) retrieved from the local database, ii) provided by the HLR/AuC, or iii) provided by the previously visited R99+ VLR/SGSN, or b) provided as a triplet by the previously visited VLR/SGSN. NOTE 1: R99+ VLR/SGSN will always provide quintets for UMTS subscribers. NOTE 2: For a UMTS subscriber, all triplets are derived from quintets, be it in the HLR/AuC or in an VLR/SGSN. GSM AKA results in the establishment of a GSM security context; the 64-bit GSM cipher key Kc and the cipher key sequence number CKSN are stored in the VLR/SGSN. In this case the user is attached to a GSM BSS. When the user receives service from an MSC/VLR, the 64-bit GSM cipher key is sent to the BSC (and forwarded to the BTS). When the user receives service from an SGSN, the derived cipher key Kc is applied in the SGSN itself. UMTS authentication and key freshness cannot be provided to UMTS subscriber with R98- ME.