Section: 4.4.4.2 Integrity checking of NAS signalling messages in the UE
Content: Except the messages listed below, no NAS signalling messages shall be processed by the receiving EMM entity in the UE or forwarded to the ESM entity, unless the network has established secure exchange of NAS messages for the NAS signalling connection: - EMM messages: - IDENTITY REQUEST (if requested identification parameter is IMSI); - AUTHENTICATION REQUEST; - AUTHENTICATION REJECT; - ATTACH REJECT (if the EMM cause is not #25 or #78); - DETACH ACCEPT (for non switch off); - TRACKING AREA UPDATE REJECT (if the EMM cause is not #25 or #78); - SERVICE REJECT (if the EMM cause is not #25 or #78). NOTE: These messages are accepted by the UE without integrity protection, as in certain situations they are sent by the network before security can be activated. All ESM messages are integrity protected. Once the secure exchange of NAS messages has been established, the receiving EMM or ESM entity in the UE shall not process any NAS signalling messages unless they have been successfully integrity checked by the NAS. If NAS signalling messages, having not successfully passed the integrity check, are received, then the NAS in the UE shall discard that message. The processing of the SECURITY MODE COMMAND message that has not successfully passed the integrity check is specified in clause 5.4.3.5. If any NAS signalling message is received as not integrity protected even though the secure exchange of NAS messages has been established by the network, then the NAS shall discard this message.