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 "Ki". The "Ki" is securely burned into the SIM during manufacture and is also securely replicated onto the AuC. This "Ki" is never transmitted between the AuC and SIM, but is combined with the IMSI to produce a challenge/response for identification purposes and an encryption key called "Kc" for use in over the air communications.