A Ciphering Key (CK) and an Integrity Key (IK) are generated by the Core Network (CN) and the UE respectively, using a shared secret and a random number (RAND) that is transferred from the CN to the UE during Non Access Stratum (NAS)-level authentication procedures. The Direction bit depends on whether it is an uplink (UL) or a downlink (DL). The COUNT-I for Radio Resource Control (RRC) and Radio Link Control (RLC) Protocol Data Unit (PDU)s and COUNT-C are parameters that increment every RLC PDU. The structure of the COUNT-C depends on the RLC mode used and is shown in FIG. 3.saf12zcv545%K:JFD()$#_*(本文来自移动通信网www.mscbsc.com,版权所有
The structure of the COUNT-I is shown in FIG. 4.
Both COUNT-C and COUNT-I are initialized by the UE and the RNC using the parameter START sent by the UE in its RRC Connection Setup Complete message. The FRESH parameter is generated by the RNC and sent to the UE in its Security Mode Command.&#*($(哦*K:JFD()$#本文来自移动通信网www.mscbsc.com,版权所有
The CK, IK, COUNT-C, COUNT-I and FRESH parameters along with the ciphering and integrity protection procedures being used, constitute the security context that is necessary for the UE and RNC (or in the new system, the eNB) to perform ciphering and/or integrity protection. For example, an eNB and a UE must share common keys and integrity procedures in order to properly communicate data/information between them.
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