How is authentication implemented in GSM?

A.
Using public key cryptography

B.
It is not implemented in GSM

C.
Using secret key cryptography

D.
Out-of-band verification

Explanation:
Authentication is effected in GSM through the use of a common
secret key, Ks, that is stored in the network operator’s Authentication
Center (AuC) and in the subscriber’s SIM card. The SIM card may be in
the subscriber’s laptop, and the subscriber is not privy to Ks. To begin
the authentication exchange, the home location of the subscriber’s
mobile station, (MS), generates a 128-bit random number (RAND) and
sends it to the MS. Using an algorithm that is known to both the AuC
and MS, the RAND is encrypted by both parties using the secret key,
Ks. The ciphertext generated at the MS is then sent to the AuC and
compared with the ciphertext generated by the Auc. If the two results
match, the MS is authenticated and the access request is granted. If
they do not match, the access request is denied. The other answers are, therefore, incorrect.