The random number (RAND) is used to check the subscriber's network access authorization in GSM networks
. The generation of a random number is based on a cryptic procedure for which the challenge-response method
. Thegenerated RAND is then transmitted to the mobile station
, anda 32-bit long value is calculated from the RAND number using the secret key and the A3 algorithm, both of which are stored on the SIM card
(SRES) and compared with the value calculated there. If the values match, the subscriber
isauthorized to access
The advantage of this procedure is that no personal data and keys are transmitted for the network access authorization check.