Patent ID: 8683194

Claim:
A secure communications method for use in a telecommunications network, wherein a transaction between an entity A and an entity B of said network comprises the following steps: a) the entity A sends an authorization request to an Authorization Server S, in which request the entity A identifies itself and authenticates itself as the holder of an identifier ID A ; b) the entity A declares to the Authorization Server S its intention to communicate with a certain entity B; the Authorization Server S determines a secret key K SB that it shares with the entity B; and c) the Authorization Server S generates a session key K AB,N and sends it to the entity A; wherein said session key K AB,N is a one-way function of said secret key K SB and is also a function of an integer N allocated to said transaction, which integer is referred to as the transaction number, and further comprising the following steps: d) the Authorization Server S also generates a transaction identifier IDTR N that is a function depending at least on said transaction number N in non-invertible manner; e) the Authorization Server S causes elements to reach the entity B, which elements comprise at least said transaction identifier IDTR N ; and f) the entity B verifies at least that the value of the transaction identifier IDTR N received during said step e) appears within a set of values precalculated by the entity B and corresponding to at least one predicted value for a transaction number; if so, the entity B deduces therefrom firstly the current value of the transaction number N and subsequently the value of the session key K AB,N .