Section: 4.7.1.2a.3 Integrity checking of layer 3 signalling messages in the network
Content: Except the messages listed below, no GMM signalling messages shall be processed by the receiving GMM entity in the network or forwarded to the SM entity, unless integrity protection has been successfully negotiated: - GMM messages: - ATTACH REQUEST; - IDENTITY RESPONSE (if requested identification parameter is IMSI); - AUTHENTICATION AND CIPHERING FAILURE; - DETACH REQUEST; - DETACH ACCEPT. All SM messages are integrity protected. Once a valid UMTS security context exists, until integrity protection has been successfully negotiated, the receiving GMM entity in the network shall process the following GMM signalling messages, even if the MAC included in the LLC frame carrying the GMM message fails the integrity check or cannot be verified in the LLC layer, as the UMTS security context is not available in the network: - ATTACH REQUEST; - IDENTITY RESPONSE (if requested identification parameter is IMSI); - AUTHENTICATION AND CIPHERING FAILURE; - DETACH REQUEST (if sent before integrity protection has been activated); - DETACH ACCEPT; - ROUTING AREA UPDATE REQUEST; NOTE: These messages are processed by the GMM layer even when the MAC fails the integrity check or cannot be verified, as in certain situations they can be sent by the MS protected with an UMTS security context that is no longer available in the network. If an ATTACH REQUEST message fails the integrity check, the network shall authenticate the subscriber before processing the attach request any further. If a ROUTING AREA UPDATE REQUEST message fails the integrity check, the network shall initiate an re-authentication of the subscriber by initiating an authentication and ciphering procedure. Once integrity protection has been successfully negotiated, the receiving GMM or SM entity in the network shall not process any GMM or SM signalling messages unless they have been successfully integrity checked by the LLC layer. If any GMM or SM signalling message, having not successfully passed the integrity check, is received, then the LLC layer in the network discards that message. The processing of the AUTHENTICATION AND CIPHERING RESPONSE message when authentication is taking place, that has not successfully passed the integrity check at GMM layer is specified in subclause 4.7.7.3. If any GMM or SM signalling message is received, as not integrity protected even though integrity protection has been successfully negotiated, then the GMM layer shall discard this message.