Section: 4.1.1.1.1 Integrity Checking of Signalling Messages in the Mobile Station (Iu mode only)
Content: In Iu mode only, integrity protected signalling is mandatory with one exception regarding emergency calls (see subclause 4.1.1.1.1a). In Iu mode only, all layer 3 protocols shall use integrity protected signalling once the security mode procedure has been successfully activated in the network and the MS. Integrity protection of all layer 3 signalling messages is the responsibility of lower layers. It is the network which activates integrity protection. This is done using the security mode control procedure (3GPP TS 25.331[ None ]  [23c] and 3GPP TS 44.118[ None ]  [111]). The supervision that integrity protection is activated shall be the responsibility of the MM and GMM layer in the MS (see 3GPP TS 33.102[ 3G security; Security architecture ]  [5a]). In order to do this, the lower layers shall provide the MM and GMM layer with an indication on when the integrity protection is activated in the MS (i.e. one indication to the MM layer when a security mode control procedure for the CS domain is processed successfully and one indication to the GMM layer when a security mode control procedure for the PS domain is processed successfully). The CS and PS domains in the network and the MM and GMM layers in the MS, are not aware of whether integrity protection has been started in the lower layers by the other domain. It is mandatory for the network to initiate one security mode control procedure for the CS domain and one for the PS domain. Except the messages listed below, no layer 3 signalling messages shall be processed by the receiving MM and GMM entities or forwarded to the CM entities, unless the network has activated the integrity protection for that domain. - MM messages: - AUTHENTICATION REQUEST - AUTHENTICATION REJECT - IDENTITY REQUEST - LOCATION UPDATING ACCEPT (at periodic location update with no change of location area or temporary identity, and, any Per MS T3212 value is not changed) - LOCATION UPDATING REJECT (if the cause is not #25) - CM SERVICE ACCEPT, if the following two conditions apply: - no other MM connection is established; and - the CM SERVICE ACCEPT is the response to a CM SERVICE REQUEST with CM SERVICE TYPE IE set to 'emergency call establishment' - CM SERVICE REJECT (if the cause is not #25) - ABORT - GMM messages: - AUTHENTICATION & CIPHERING REQUEST - AUTHENTICATION & CIPHERING REJECT - IDENTITY REQUEST - ATTACH REJECT (if the cause is not #25) - ROUTING AREA UPDATE ACCEPT, if any of the following conditions applies: - the MS performs periodic routing area updating with: - no change in routing area or temporary identities; - no change in T3312 extended value; - no change in Network feature support value; and - extended DRX parameters IE not included. - the GMM entity in the MS has received an ATTACH ACCEPT message with neither ciphering nor integrity protection applied in response to an ATTACH REQUEST message with attach type set to "emergency attach"; or - the MS has performed intersystem change from S1 mode to Iu mode with a PDN connection for emergency bearer services for which the "null integrity protection algorithm" EIA0 has been used while in S1 mode. - ROUTING AREA UPDATE REJECT (if the cause is not #25) - SERVICE REJECT (if the cause is not #25) - DETACH ACCEPT (for non power-off) - ATTACH ACCEPT, if the ATTACH ACCEPT is the response to an ATTACH REQUEST with attach type set to "emergency attach". - SERVICE ACCEPT, if any of the following conditions applies: - the GMM entity in the MS has received an ATTACH ACCEPT message with neither ciphering nor integrity protection applied in response to an ATTACH REQUEST message, with attach type set to "emergency attach"; or - the MS has performed intersystem change from S1 mode to Iu mode with a PDN connection for emergency bearer services for which the "null integrity protection algorithm" EIA0 has been used while in S1 mode. - CC messages: - all CC messages, if the following two conditions apply: - no other MM connection is established; and - the MM entity in the MS has received a CM SERVICE ACCEPT message with no ciphering or integrity protection applied as response to a CM SERVICE REQUEST message, with CM SERVICE TYPE set to 'Emergency call establishment’ sent to the network; - the MM connection was established locally due to the SRVCC handover of a PDN connection for emergency bearer services for which the "null integrity protection algorithm" EIA0 has been used while in S1 mode or for which integrity protection has not been activated while in Iu mode; or - the MM connection was established locally due to the 5G-SRVCC handover from NG-RAN to UTRAN of an emergency PDU session for which the "null integrity protection algorithm" 5G-IA0 has been used while in N1 mode. - SM messages: - all SM messages, if any of the following conditions applies: - the GMM entity in the MS has received an ATTACH ACCEPT message with neither ciphering nor integrity protection applied in response to an ATTACH REQUEST message, with attach type set to "emergency attach"; or - the MS has performed intersystem change from S1 mode to Iu mode with a PDN connection for emergency bearer services for which the "null integrity protection algorithm" EIA0 has been used while in S1 mode. Once integrity protection is activated, the receiving layer 3 entity in the MS shall not process any layer 3 signalling messages unless they have been successfully integrity checked by the lower layers. If any signalling messages, having not successfully passed the integrity check, are received, then the lower layers in the MS shall discard that message (see 3GPP TS 25.331[ None ]  [23c] and 3GPP TS 44.118[ None ]  [111]). If any layer 3 signalling message is received, in either PS or CS domains, as not integrity protected even though the integrity protection has been activated in the MS by that domain in the network, then the lower layers shall discard this message (see 3GPP TS 25.331[ None ]  [23c] and 3GPP TS 44.118[ None ]  [111]). Integrity checking on the network side is performed by the RNC and is described in 3GPP TS 25.331[ None ]  [23c] and 3GPP TS 44.118[ None ]  [111].