name: CK
full_form: Ciphering Key
context: The cipher key CK is 128 bits long. There may be one CK for CS connections (CKCS), established between the CS service domain and the user and one CK for PS connections (CKPS) established between the PS service domain and the user. The CK to use for a particular radio bearer is described in 6.6.5. For UMTS subscribers, CK is established during UMTS AKA, as the output of the cipher key derivation function f3, available in the USIM and in HLR/AuC. For GSM subscribers that access the UTRAN, CK is established following GSM AKA and is derived from the GSM cipher key Kc, as described in 8.2. CK is stored in the USIM and a copy is stored in the ME. CK is sent from the USIM to the ME upon request of the ME. The USIM shall send CK under the condition that a valid CK is available. The ME shall trigger a new authentication procedure if the current value of STARTCS or STARTPS in the USIM have reached THRESHOLD. The ME shall delete CK from memory after power-off as well as after removal of the USIM.
description: The Ciphering Key (CK) is a critical network attribute used for encrypting and decrypting data in telecommunications, specifically in UMTS and GSM networks. It is a 128-bit key established during authentication procedures, such as UMTS AKA or GSM AKA, and stored in the USIM and ME.
explanation: The context explicitly describes CK as a key used for ciphering, which justifies its classification as a Parameter. The detailed description of its establishment, storage, and usage within the network further supports this categorization.
section_title: 6.6.4.2	CK
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