algorithm 3 (A3)

The A3 algorithm is an encryption for the authentication of the mobile subscriber in GSM networks.

The A3 algorithm works according to the challenge- response method and is implemented in the SIM card and in the Authentication Center( AC) of the GSM network. The A3 algorithm can be specified by the GSM network operator, but it does not apply to all carriers and is thus not uniform in GSM. It is used to authenticate the subscriber and to generate a key for encrypting voice and data traffic. When generating the encryption key, a random number(RAND) is associated with the key. In practice, the A3 algorithm is implemented together with the A8 algorithm.