Section: 4.7.1.2a.6 Change of security keys
Content: When the network initiates a re-authentication to create a new UMTS security context, the AUTHENTICATION AND CIPHERING REQUEST message and AUTHENTICATION AND CIPHERING RESPONSE message exchanged during the authentication and ciphering procedure are integrity protected with the new UMTS security context at GMM layer by including a MAC. The AUTHENTICATION AND CIPHERING REQUEST message and AUTHENTICATION AND CIPHERING RESPONSE message may be also integrity protected at the LLC layer using the current UMTS security context, if any. Both UE and network shall continue to use the current UMTS security context, until the network initiates a re-authentication in the authentication and ciphering procedure. The AUTHENTICATION AND CIPHERING REQUEST message sent by the network includes the CKSN of the new UMTS security context to be used. The SGSN shall send the AUTHENTICATION AND CIPHERING REQUEST message integrity protected with the new UMTS security context at GMM layer by including a MAC, but unciphered. When the UE responds with an AUTHENTICATION AND CIPHERING RESPONSE message, it shall send the message integrity protected with the new UMTS security context at GMM layer by including a MAC, but unciphered. The UE shall take the new UMTS security context and the indicated integrity algorithm and encryption algorithm received in the AUTHENTICATION AND CIPHERING REQUEST message, into use in the LLC layer after sending the AUTHENTICATION AND CIPHERING RESPONSE message. The network shall take the new UMTS security context and the indicated integrity algorithm and encryption algorithm sent in the AUTHENTICATION AND CIPHERING REQUEST message, into use in the LLC layer in the network after receiving the AUTHENTICATION AND CIPHERING RESPONSE message and a successful check of the RES.