IMS-AKA (IMS Authentication and Key Agreement)

Also known as: IMS Authentication and Key Agreement, TS 33.203 AKA

IMS-AKA is the authentication and key agreement protocol used to register a subscriber with the IMS core over the Gm interface. It reuses the 3GPP AKA challenge-response run between the ISIM and the HSS, carried inside SIP REGISTER exchanges with the P-CSCF, and derives keys that protect the SIP signalling with IPsec ESP in transport mode. IMS-AKA is specified in 3GPP TS 33.203 and is mandatory for VoLTE and VoNR access to the IMS.

Categories: Radio Access NetworkCore NetworkSignaling

IMS-AKA in context

The radio access network is the layer where mobile devices attach to the operator's infrastructure. Attacks in this layer include IMSI catching, rogue base stations, downgrade attacks and jamming, and defenses hinge on mutual authentication, integrity-protected signaling and Open RAN supply-chain hygiene.

The mobile core is where subscriber sessions, mobility and policy live. In 4G it is the EPC (MME, HSS, S/PGW); in 5G it is the Service-Based Architecture with AMF, SMF, UPF, AUSF, UDM and the NRF. Core exposure is the difference between a single-subscriber leak and a fleet-wide breach.

To place IMS-AKA in the wider telecom-security picture, review IPsec, GTP-U, N3, IAP, User Plane Security and NGAP.

Related terms

Equipment

IMS core (CSCF, TAS, MRF, MGCF, BGCF)

Articles in the P1 mobile network security guide

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