name: CKSN
full_form: Ciphering Key Sequence Number
context: At PS to CS domain change from S1 mode due to SRVCC or vSRVCC handover of a PDN connection for which the "null integrity protection algorithm" EIA0 has not been used (see 3GPP TS 23.216 [126]), when the MS receives the command to perform handover, the MS shall derive a UMTS security context for the CS domain from the current EPS security context. The MS shall set the CKSN of the derived UMTS security context to the value of the eKSI of the EPS security context and derive security keys CKSRVCC and IKSRVCC as specified in 3GPP TS 33.401 [123]. The ME shall also derive the security key GSM ciphering key Kc from CKSRVCC and IKSRVCC using the conversion function c3 as specified in 3GPP TS 33.102 [5a]. The MS shall apply these derived security keys, handle the STARTCS value as specified in 3GPP TS 25.331 [23c] and replace an already established UMTS security context for the CS domain, if any, in the USIM, when the SRVCC or vSRVCC handover from S1 mode has been completed successfully. NOTE: Because of deriving a new UMTS security context for the CS domain, a new GSM ciphering key needs also to be derived from the new derived UMTS security keys for the CS domain (i.e. CKSRVCC and IKSRVCC). Note that the new GSM ciphering key is also part of the new UMTS security context for the CS domain as well, as 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 used. The network shall replace an already established UMTS security context for the CS domain, if any, when the SRVCC or vSRVCC handover from S1 mode has been completed successfully. If the SRVCC or vSRVCC handover from S1mode 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.
description: The CKSN is an identifier for the ciphering key used in mobile networks.
explanation: Categorized as a Key Identifier because it uniquely identifies a ciphering key.
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biotag_Description: O,B-Parameter,O,O,O,O,O,O,O,O,O,O,O