Section: 4.3.2.11.1 PDN connection with integrity protection
Content: At PS to CS domain change from Iu mode to Iu mode due to SRVCC handover of a PDN connection for which integrity protection has been activated, ciphering and integrity may be started (see 3GPP TS 25.331[ None ]  [23c]) without any new authentication procedure. Deduction of the appropriate security keys for ciphering and integrity check in Iu mode, depends on the current GSM or UMTS security context for the PS domain stored in the MS and the network. The ME shall handle the UMTS ciphering key and the UMTS integrity key according to table 4.3.2.11.1. Table 4.3.2.11.1/3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ] : SRVCC handover from Iu mode to Iu mode NOTE 1: For the case of an established UMTS security context for the PS domain, because of deriving a new UMTS security context for the CS domain, a new GSM ciphering key needs to be derived from the new derived UMTS security keys (i.e. CK' and IK'). Note that the new GSM ciphering key is also part of the new UMTS security context for the CS domain, and therefore any old GSM ciphering key stored in the USIM and in the ME belongs to an old UMTS security context for the CS domain and can no longer be taken into use. The network shall replace an already established GSM or UMTS security context for the CS domain, if any, when the SRVCC handover from Iu mode to Iu mode has been completed successfully. If the SRVCC handover from Iu 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 CS domain. Additionally, the network shall delete the already established GSM or UMTS security context for the CS domain, if the CKSN of the already established GSM or UMTS security context is equal to the CKSN of the new derived GSM or UMTS security context for the CS domain.