Section: 4.3.2.7 Handling of keys at intersystem change from Iu mode to A/Gb mode
Content: At inter-system change from Iu mode to A/Gb mode, ciphering may be started (see 3GPP TS 44.018[ None ]  [84]) without any new authentication procedure. Deduction of the appropriate security key for ciphering in A/Gb mode, depends on the current GSM/UMTS security context stored in the MS and the network. The ME shall handle the GSM ciphering key and a potential GSM Kc128 according to table 4.3.2.7.1. Table 4.3.2.7.1/3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ] : Inter-system change from Iu mode to A/Gb mode NOTE: A USIM with UMTS security context, passes the UMTS ciphering key, the UMTS integrity key and the derived GSM ciphering key to the ME independent on the current radio access being UTRAN or GERAN.