Patent ID: 7900051

Claim:
A multimedia digital data transmission system, comprising: a sender including a message insertion device; and a receiver including a message decoding device; the message insertion device of the sender configured to: authenticate the receiver by a symmetrical authentication key sharing algorithm with no transmission of the key; watermark data by using the authentication key as the watermarking key; and transmit the watermarked data, wherein authenticating the receiver includes: 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; 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; 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.