The Authentication Center (AUC) is a facility in GSM networks and Tetra networks that serves to authenticate mobile subscribers. Authentication itself is performed by identifying and verifying the data stored on the SIM card.
Once the subscriber is authenticated, the Authentification Center generates the security parameters relevant to the GSM network. These include the storage of the secret authentication key( Ki), the session key( Kc), which is generated from the authentication key and a random number, and authentication via the challenge- response method. The authentication center sends the random number(RAND) to the mobile station, receives its response, and compares it with a self-generated value.