Patent ID: 7222237

Claim:
A secure method of digital data transmission between a sender and a receiver, including the following phases: receiver authentication by a symmetrical authentication key sharing algorithm with no transmission of the key; data watermarking by using the authentication key as the watermarking key; and transmission of the watermarked data, wherein the authentication phase includes the steps of: transmission, from the sender to the receiver, at least of a random number and of an identifier of the sender; calculation of the authentication key by the receiver based at least on the sender identifier and on a secret quantity of the receiver; transmission, from the receiver to the sender, at least of an identifier of the receiver and of a first quantity representing said random number, encrypted with the authentication key calculated by the receiver; and calculation of the authentication key by the sender based at least on the identifier of the receiver and on a secret quantity of the sender, wherein the step of authentication key calculation by the sender is followed by the steps of: calculation of a second quantity representing said random number, encrypted with the authentication key calculated by the sender; and identity checking between the first and second encrypted quantities.