Section: 4.3.2.13 Derivation of keys at CS to PS SRVCC handover from A/Gb mode to Iu mode
Content: At change from A/Gb mode to Iu mode due to CS to PS SRVCC handover (see 3GPP TS 23.216[ Single Radio Voice Call Continuity (SRVCC); Stage 2 ]  [126]), the MS shall derive a UMTS security context for the PS domain from the current GSM or UMTS security context for the CS domain. At change from A/Gb mode to Iu mode due to CS to PS SRVCC handover, ciphering may be started and integrity protection shall be started (see 3GPP TS 25.331[ None ]  [23c]) without any new authentication procedure. Derivation of the appropriate security keys for ciphering and integrity protection for the PS domain in Iu mode depends on the current GSM or UMTS security context for the CS domain stored in the MS and the network. The ME shall handle the PS UMTS ciphering key and the PS UMTS integrity key according to table 4.3.2.13.1. Table 4.3.2.13.1/3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ] : CS to PS SRVCC handover from A/Gb mode to Iu mode The network shall replace an already established GSM or UMTS security context for the PS domain, if any, when the CS to PS SRVCC handover from A/Gb mode to Iu mode has been completed successfully. If the CS to PS SRVCC handover from A/Gb mode to Iu mode has not been completed successfully, the MS and the network shall delete the new derived GSM or UMTS security context for the PS domain. Additionally, the network shall delete the already established GSM or UMTS security context for the PS domain, if the GPRS CKSN of the already established GSM or UMTS security context is equal to the GPRS CKSN of the new derived GSM or UMTS security context for the PS domain.