A secure communications method is provided for use in a telecommunications network, wherein a transaction between an entity A and an entity B of the network comprises: entity A sending an authorization request to an Authorization Server S, in which request the entity A identifies itself and authenticates itself; the entity A declares to the Authorization Server its intention to communicate with a certain entity B; the Authorization Server determines a secret key that it shares with the entity B; the Authorization Server generates a session key and sends it to the entity A; the session key being a one-way function of the secret key and also being a function of an integer (transaction number) allocated to the transaction; the Authorization Server also generates a transaction identifier that is a function depending at least on the transaction number in non-invertible manner.