Editing Network switching subsystem (section)

===Description===
The '''authentication center''' (AuC) is a function to [[authentication|authenticate]] each [[SIM card]] that attempts to connect to the '''gsm''' core network (typically when the phone is powered on). Once the authentication is successful, the HLR is allowed to manage the SIM and services described above. An [[encryption key]] is also generated that is subsequently used to encrypt all wireless communications (voice, SMS, etc.) between the mobile phone and the GSM core network.

If the authentication fails, then no services are possible from that particular combination of SIM card and mobile phone operator attempted. There is an additional form of identification check performed on the serial number of the mobile phone described in the EIR section below, but this is not relevant to the AuC processing.

Proper implementation of security in and around the AuC is a key part of an operator's strategy to avoid [[SIM cloning]].

The AuC does not engage directly in the authentication process, but instead generates data known as ''triplets'' for the MSC to use during the procedure.  The security of the process depends upon a [[shared secret]] between the AuC and the SIM called the ''K<sub>i</sub>''. The ''K<sub>i</sub>'' is securely burned into the SIM during manufacture and is also securely replicated onto the AuC. This ''K<sub>i</sub>'' is never transmitted between the AuC and SIM, but is combined with the IMSI to produce a [[Challenge–response authentication|challenge/response]] for identification purposes and an encryption key called ''K<sub>c</sub>'' for use in over the air communications.