Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1996-01-11
1998-03-17
Cangialosi, Salvatore
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380 25, 380 44, H04L 908
Patent
active
057296090
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for producing a common key K assigned to an arbitrary device CE.sub.k of a set of first devices CE and to an arbitrary device PME.sub.i of a set second devices PME so that these two devices will implement a common cryptographic procedure.
DESCRIPTION OF RELATED ART
A conventional method consists of assigning all the first devices CE a common mother key, and all the second devices PME a different daughter key, obtained by diversification of the mother key by means of an identification datum of the second device in question.
A hierarchy is thus established between the first and second devices, since the level of security of the first devices is higher than that of the second devices.
During a session between a first device CE and a second device PME, the latter transmits its identification datum to the former, in such a way that the first device calculates the daughter key of the second device on the basis of its mother key; this daughter key constitutes the common key K.
This method is satisfactory in the event of attempted fraud at one of the second devices PME. The violation of the second device PME will allow the defrauder to discover only one daughter key at best, but not to learn the mother key, which would be the only one that could allow him to produce new, fraudulent daughter keys compatible with the mother key in order to fabricate fraudulent second devices PME.
However, if the defrauder violates one of the first devices CE, there is the risk that he can gain access to the mother key.
SUMMARY OF THE INVENTION
The problem the invention seeks to solve is to propose a method of the type defined at the outset above that offers good immunity to violation of an arbitrary one of the two devices PME and CE between which a common cryptographic procedure takes place.
To that end, the method of the invention includes the steps comprising assigning a first mother key KC to each of said first devices CE, and a second mother key KP to each of said second devices PME; assigning at least one daughter key KP.sub.ck to each first device CE.sub.k, based on the second mother key KP relating to the second devices PME.sub.i and on an identification datum ck assigned to this first device CE.sub.k ; assigning at least one daughter key KC.sub.pi to each second device PME.sub.i, based on the first mother key KC relating to the first devices CE.sub.k and on an identification datum pi assigned to the second device PME.sub.i, each time a cryptographic procedure between a first device PME.sub.i and a second device CE.sub.k is requested; transmitting the identification datum pi, ck from each of these two devices to the other device; in each of these two devices, developing a daughter key KP.sub.ck, KC.sub.pi, based on the mother key KP, KC of the applicable device and on the identification datum ck, pi received from the other device; in each of these two devices, selecting the daughter key KC.sub.pi, KP.sub.ck corresponding to the identification datum pi, ck received from the other device; and associating the two daughter keys constituted by the daughter key KP.sub.ck ; KC.sub.pi developed on the occasion of this procedure and the daughter key selected KC.sub.pi ; KP.sub.ck to form a pair constituting said common key K.
Thus, surprisingly, the most secret data, that is, the mother keys KC, KP, are distributed in the first and second devices, moreover regardless of the difference in hierarchical level that may exist between the two sets of devices and may be associated with the application in question (as an example, between a data base server and a terminal that provides access to it, or between an electronic cash register of a merchant and an electronic billfold of a customer). With respect to the nature of the keys held by the first and second devices, both devices have the same level of security.
Violating a first or second device PME.sub.i at best allows the defrauder to procure one of the mother keys, KP, but not the other, KC. To the extent that the daughter k
REFERENCES:
patent: 5204901 (1993-04-01), Hershey
patent: 5602915 (1997-02-01), Campana et al.
Ramesh Karri `IEEE INFOCOM`88. "The Conference on Computer Communications: Proceedings. A Security Imbedded Authentication Protocol" Mar. 1988, Institute of Electrical & Electronics Engineers, New Orleans, US XP 000093591 152169.
Dawirs Michel
Hazard Michel
Moulart Yves
Cangialosi Salvatore
CP8 Transac
Kondracki Edward J.
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