Method of authenticating a transponder in communication with a server, the transponder comprising a processing unit linked to a memory unit, to a counter and to wireless linking means so as to establish a communication with the server, characterised in that the method comprises the steps of: - incrementing the counter value of the transponder by a new random number generated in the processing unit, the incrementation resulting in a new value of the transponder counter, - defining a Nonce word in the processing unit of the transponder during a communication operation, where the Nonce consists of the new counter value of the transponder, - calculating a first one-time password in the processing unit of the transponder with the aid of a dedicated algorithm, the said algorithm being stored, and of a secret key on the basis of the Nonce word generated in the processing unit, - transmitting the Nonce word and the first one-time password to the server, by checking, that the Nonce word received from the transponder is a new value strictly greater than the previous value of the Nonce word from a previous use or reading, - calculating a second one-time password in the server on the basis of the secret key and the Nonce word received from the transponder by means of one and the same dedicated algorithm identical to that of the transponder, - checking whether the second one-time password calculated is identical to the first one-time password received from the transponder so as to authenticate the transponder and authorise access to a site determined by the server by having verified knowledge of the secret key used to calculate the first and second passwords in the transponder and the server, in that at each reading of the transponder, the state of the counter for generating the Nonce authentication word is incremented by a random number lying between 1 and M, where M is an integer number, and in that the count size of the counter of the transponder is P times greater than the random increment M, this number P, which is an integer number, being at least equal to 256 times greater than the number M. - incrementing the counter value of the transponder by a new random number generated in the processing unit, the incrementation resulting in a new value of the transponder counter, - defining a Nonce word in the processing unit of the transponder during a communication operation, where the Nonce consists of the new counter value of the transponder, - calculating a first one-time password in the processing unit of the transponder with the aid of a dedicated algorithm, the said algorithm being stored, and of a secret key on the basis of the Nonce word generated in the processing unit, - transmitting the Nonce word and the first one-time password to the server, by checking, that the Nonce word received from the transponder is a new value strictly greater than the previous value of the Nonce word from a previous use or reading, - calculating a second one-time password in the server on the basis of the secret key and the Nonce word received from the transponder by means of one and the same dedicated algorithm identical to that of the transponder, - checking whether the second one-time password calculated is identical to the first one-time password received from the transponder so as to authenticate the transponder and authorise access to a site determined by the server by having verified knowledge of the secret key used to calculate the first and second passwords in the transponder and the server, in that at each reading of the transponder, the state of the counter for generating the Nonce authentication word is incremented by a random number lying between 1 and M, where M is an integer number, and in that the count size of the counter of the transponder is P times greater than the random increment M, this number P, which is an integer number, being at least equal to 256 times greater than the number M.