H.8 Definition of MAC-GMM in GMM Authentication and Ciphering Request and GMM Authentication and Ciphering Response messages

3GPP43.020Release 16Security related network functionsTS

H.8.1 Inputs and outputs

The following description in this clause is only applicable to when the GMM Authentication and Ciphering procedure is used for authentication. This clause is not applicable to the use case when the GMM Authentication and Ciphering procedure is used for switchin algorithm or setting the GSM ciphering mode only (and not used for authentication). The SGSN and UE shall not calculate and include a MAC-GMM in the GMM protocol for the GMM Authentication and Ciphering Request and GMM Authentication and Ciphering Response messages when no authentication takes place in the Authentication and Ciphering procedure.

NOTE: The MAC-GMM is not present when the ciphering or integrity protection algorithms are changed.

The SGSN shall include a MAC-GMM in the GMM Authentication and Ciphering Request message and the UE shall include a MAC-GMM in the GMM Authentication and Ciphering Response message; to be used for integrity protection and replay protection of the GMM messages. The MAC-GMM is a 32-bit message authentication code that protects the integrity of the GMM message. The SGSN and the UE calculate the MAC-GMM at the GMM protocol layer using the Ki128 integrity key. The GMM message shall be integrity protected with the same selected integrity algorithm to be used in LLC layer (see H.5.3).

In order to calculate the MAC-GMM for the GMM Authentication and Ciphering Request message, the SGSN shall use the following inputs:

– Integrity key Ki128 shall be set to Ki128 integrity key used in LLC layer;

– all Input-I bits shall be set to 0;

– MESSAGE shall be set to the GMM Authentication and Ciphering Request message, with all bits of the value part of the Message authentication code information element set to zero;

– DIRECTION bit shall be set to 1;

– FRAMETYPE=255;

The MAC-GMM shall be the 32 least significant bits of the output of the used integrity algorithm.

The GMM layer in the UE checks and verifies the MAC-GMM received in GMM Authentication and Ciphering Request message in the same way as the SGSN as described above by using the integrity key Ki128.

If the UE receives a GMM Authentication and Ciphering Request message without a MAC-GMM parameter then the UE shall silently discard the message.

If the verification of the MAC-GMM received in the GMM Authentication and Ciphering Request message is not successful in the UE, then the UE shall silently discard the message.

In order to calculate the MAC-GMM for GMM Authentication and Ciphering Response message, the UE shall use the following inputs:

– Integrity key Ki128 shall be set to Ki128 integrity key used in LLC layer;

– all Input-I bits shall be set to 0;

– MESSAGE shall be set to the GMM Authentication and Ciphering Response message, with all bits of the value part of the Message authentication code information element replaced with zero;

– DIRECTION bit shall be set to 0;

– FRAMETYPE=255;

The MAC-GMM shall be the 32 least significant bits of the output of the used integrity algorithm.

The GMM layer in the SGSN checks and verifies the MAC-GMM received in GMM Authentication and Ciphering Response message in the same way as the UE as described above by using the integrity key Ki128.

If the SGSN receives a GMM Authentication and Ciphering Response message without a MAC-GMM parameter then the SGSN shall silently discard the message.

If the check and verification of the received MAC-GMM in the GMM Authentication and Ciphering Response message is not successful in the SGSN, then the SGSN shall ignore the message.