Patent ID: 8336087

Claim:
A method, performed by an authentication server, of authenticating a user in a communication system comprising a user terminal and the authentication server which is capable of storing two types of nonce values comprising dedicated nonce values unique in the system and common nonce values constant and common to all users managed by the authentication server during a fixed time period, the method comprising: receiving from the user terminal an access request; determining, using a given criterion, the type of a first nonce value to be sent to the user terminal as a response to the access request, wherein, in case the given criterion is fulfilled the type of the first nonce value is a dedicated nonce value, otherwise the type of the first nonce value is a common nonce value which is constant and common to all of the users managed by the authentication server during the fixed time period; sending the first nonce value which has been determined; receiving a response from the user terminal, the response comprising a second nonce value and a response code to the first nonce value sent by the authentication server; and determining whether the response code is correct and whether the second nonce value corresponds to the first nonce value sent by the authentication server.