GSM
Last updated
Last updated
Based on a secret key shared between the HLR and the station.
128 Ki, stored in the station’s SIM card.
Can only be used after entering a PIN.
Algorithms (initially not public):
A3 for authentication.
A8 for generating a session key.
A5 for encrypting the communication.
A3 and A8 are implemented by SIM cards.
Can be freely selected by the operator.
MSC fetches a trio from HLR.
RAND, SRES, Kc.
More than one is requested.
HLR generates RAND and corresponding trio using the subscriber’s Ki.
RAND, random value (128 bits).
SRES = A3 (Ki, RAND) (32 bits)
Kc = A8 (Ki, RAND) (64 bits)
Usually, operators use COMP128 for A3/A8.
Recommended by the GSM Consortium.
[SRES, Kc] = COMP128 (Ki, RAND).