Section: 4.7.1.2a Integrity protection of layer 3 signalling messages (A/Gb mode only and when integrity protection is required) 4.7.1.2a.1 General
Content: The requirements in subclause 4.7.1.2a are only applicable for MSs and networks supporting EC-GSM-IoT (see 3GPP TS 43.064[ None ]  [159]). For the MS, integrity protected signalling is mandatory for the GMM messages and SM messagres once a valid UMTS security context exists and has been taken into use. For the network, integrity protected signalling is mandatory for the GMM messages and SM messages once authentication and ciphering procedure is initiated by the network. Integrity protection of all GMM signalling messages and SM messages is the responsibility of the LLC layer. In addition, the GMM layer protects the AUTHENTICATION AND CIPHERING REQUEST message and the AUTHENTICATION AND CIPHERING RESPONSE message by a message authentication code (MAC) calculated at the GMM layer when an authentication takes place in the Authentication and Ciphering procedure. This message authentication code is included in the AUTHENTICATION AND CIPHERING REQUEST message and the AUTHENTICATION AND CIPHERING RESPONSE message. The GMM layer is always using the new UMTS security context derived from the AKA taking place in the Authentication and Ciphering procedure when calculating the message authentication code (MAC) at GMM layer. The GMM layer activates integrity protection in the LLC layer by providing an indication when integrity protection shall be started. Integrity protection is initiated in the MS upon request from the network. This is done using the authentication and ciphering procedure at the GMM layer (3GPP TS 43.020[ Security related network functions ]  [13] and 3GPP TS 44.064[ Mobile Station - Serving GPRS Support Node (MS-SGSN); Logical Link Control (LLC) Layer Specification ]  [78a]). Details of the integrity protection and verification of GMM signalling messages are specified in 3GPP TS 43.020[ Security related network functions ]  [13].