Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1988-03-10
1990-03-06
Cangialosi, Salvatore
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380 24, 380 25, H04L 900
Patent
active
049072706
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for certifying the authenticity of a datum exchanged between two devices locally or remotely by a transmission line, in which each device includes at least one memory and processing circuits.
The invention is applicable in particular to memory cards remotely coupled with an external device for certifying, via the card, the authenticity of a datum transmitted by the external device or for certifying, via the external device, the authenticity of a datum transmitted by the card.
The majority of applications using memory cards use standard operations for writing and reading data in the memory on the card. The validity of these operations assumes the authenticity of the data exchanged between the card and the external device; that is, it is assumed that a datum received is indeed identical to the datum transmitted. This authenticity is not guaranteed, when the card the external device are connected remotely via a standard transmission route susceptible to observation by a defrauder capable of modifying the data in the course of transmission. This problem is a major one, especially in banking applications where the data exchanged relate to credits or debits of sums of money.
One solution to this problem may comprise enciphering the data to be transmitted, but this solution is not entirely satisfactory. In effect, the receiver deciphers the datum, in order to obtain a datum in the clear, but it is not certain that this datum does indeed correspond to the one transmitted.
The invention overcomes this disadvantage and makes it possible to authenticate a datum received as being not merely identical to the datum transmitted, but also as having been transmitted by an authorized transmitting device. Thus the invention makes it possible to detect both a datum that has been modified in the course of its transmission and a datum transmitted from an transmitter device that is not authorized.
The invention accordingly proposes 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: 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 daum (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: 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).
One advantage of the invention is that information can be written at a distance and in complete security in a receiving device, in particular comprising a portable object such as a credit card.
Further advantages, characteristics and details will become apparent from the ensuing description, referring to the accompanying drawing, which is given by way of example and schematically shows the principal elements or circuits with which the method according to the invention can be performed .
Referring to the drawing, two electronic devices (1, 2) are connected locally or at a distance by a standard transmission route (L) which is electrical or optical.
The device (1) includes at least one memory (M1), processing circuits (T1) and an input/output interface (I1). All these circuits are connected with on another via a connecting bus (b1).
The device (2) includes at
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Bull CP8
Cangialosi Salvatore
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