Method for certifying the authenticity of a datum exchanged between two devices connected locally or remotely by a transmission line

Claim 1

A method for certifying the authenticity of a datum exchanged between two transmitter and receiver devices connected by a standard transmission route, each device including at least one memory and processing circuits, characterized in that it comprises, in the transmitter device (2), fashioning an enciphered message (M) by application of the enciphering function (f2) of a nonsingular algorithm implemented by a program (P2) executed by the processing circuits (T2) and such that: M=f2(S2, X) where (S2) is the enciphering key of the algorithm prerecorded in the memory (M2) of the transmitter device (2) and (X) is a parameter organized into at least one field (X1) satisfying a predetermined condition and one field (X2) representative of the value (v) of the datum (d), transmitting this message (M) to the receiving device (1), deciphering this message (M) by application of the deciphering function (f1) of said algorithm to obtain a parameter (X') such that: X'=f1(M, S1) where (S1) is the deciphering key prerecorded in the memory (M1) of the receiving device (1), organizing the parameter (X') into at least one field (X'1) and one field (X'2), and verifying that the field (X'1) verifies the same predetermined condition as the field (X1) of the parameter (X) so as to deduce from this that the value of the datum of the field (X'2) is equal to the value of the datum (d) of the field (X2).

Claim 2

A method for certifying the authenticity of a datum exchanged between two transmitter and receiver devices connected by a standard transmission route, each device including at least one memory and processing circuits, characterized in that it comprises, in the transmitter device (2), fashioning an enciphered message (M) by application of the enciphering function (f2) of a nonsingular algorithm implemented by a program (P2) executed by the processing circuits (T2) and such that: M=f2(S2, X) where (S2) is the enciphering key of the algorithm prerecorded in the memory (M2) of the transmitter device (2) and (X) is a parameter organized into at least one field (X1) satisfying a predetermined condition and one field (X2) representative of the value (v) of the datum (d), transmitting this message (M) to the receiving device (1), deciphering this message (M) by application of the deciphering function (f1) of said algorithm to obtain a parameter (X') such that: X'=f1(M, S1) where (S1) is the deciphering key prerecorded in the memory (M1) of the receiving device (1), organizing the parameter (X') into at least one field (X'1) and one field (X'2), and verifying that the field (X'1) verifies the same predetermined condition as the field (X1) of the parameter (X) so as to deduce from this that the value of the datum of the field (X'2) is equal to the value of the datum (d) of the field (X2).