US 5,515,439 AGranted

Exchange certificate for one way validation of information

AssigneeInternational Business Machines Corporation

InventorsDavid Bantz, Frederic Bauchot, Eliane D. Bello, Shay Kutten, Hugo Krawczyk, Amir Herzberg, Yishay Mansour

Life of this patent

Estimating the term…

Loading patent…

Abstract

In a communications system, a method is described allowing two users having established a communication session identified by a unique session freshness proof, to transmit and validate a new value of a variable by using an exchange certificate which combines the following elements: the new value of the variable, a common secret key known by both users, an exchange counter representative of the number of values of said variable transmitted between the two users during the current communication session and a session freshness proof. Protection against potential eavesdroppers and intruders is provided by combining cryptographically the elements of the exchange certificate. Further protection is obtained by interrupting the current communication session and opening a new one characterized by a new unique session freshness proof when the exchange counter reaches its maximum value; thus avoiding the risk that the same value of the session freshness keeps being used when the exchange counter is reset to its initial value. Consequently a given pair of values of the session freshness proof and of the exchange counter will never be used more than one time, making eavesdropping and, replaying attacks from intruders more difficult. Preferably, the method used for opening a new communication session uses already known authentication methods based on the common secret key.

Claims18

Dependent claims

A method for transmitting a value K' of a variable, between a first user A of a communications system and a second user B, and for validating said value K', said users sharing a common secret key S and having established a first communication session identified by a first unique session freshness proof N2 known to both user A and user B, said method being characterized in that it comprises the steps of:

a. transmitting from A to B said value K' by means of an exchange certificate comprising at least two fields M1 and M2 of the minimum form:
M1=f( S, K', . . . )
M2=g( S, K', N2, c1, . . . )
wherein f( ) and g( ) are functions such that,
f( S, K', . . . )=m1 cannot be solved for K' without knowledge of S, m1 being a given value of field M1 and,
g( S, K', N2, c1, . . . )=m2 cannot be solved for K' without knowledge of S, m2 being a given value of field M2;
and wherein,
c1 is an exchange counter controlled by A and representative of the number of values of said variable exchanged between user A and user B during said first communication session;
b. processing by B of said exchange certificate M comprising the steps of:
.cndot.deriving from said exchange certificate M said value K' as a result of solving for K' equation:
f( S, K', . . . )=M1;
and
.cndot.validating said value K' as a result of the verification of a set of validation conditions comprising at least an equation of the minimum form:
g( S, K', N2, c2, . . . )=M2 wherein,
c2 is an exchange counter controlled by B and representative of the number of values of said variable exchanged between user A and user B during said first communication session.
c. interrupting at the initiative of either A or B said first communication session between A and B and opening a second communication session identified by a second unique session freshness proof upon occurrence of anyone of a set of session reset conditions, said set of reset conditions comprising failure of at least one of said validation conditions.

13 more elements

A system for transmitting a value K' of a variable, between a first user A of a communications system and a second user B, and for validating said value K', said users sharing a common secret key S and having established a first communication session identified by a first unique session freshness proof N2 known to both user A and user B, said system comprising:

a. means for transmitting from A to B said value K' by means of an exchange certificate comprising at least two fields M1 and M2 of the minimum form:
M1=f(S, K', . . . )
M2=g(S, K', N2, c1, . . . )
wherein F() and g() are functions such that,
f(S, K', . . . )=m1 cannot be solved for K' without knowledge of S, m1 being a given value of field M1 and,
g(S, K', N2, c1, . . .)=m2 cannot be solved for K' without knowledge of S, m2 being a given value of field M2;
and wherein,
c1 is an exchange counter controlled by A and representative of the number of values of said variable exchanged between user A and user B during said first communication session;
b. means for processing by B of said exchange certificate M comprising:
means for deriving from said exchange certificate M said value K' as a result of solving for K' equation:
f(S, K', . . . )=M1;
and
means for validating said value K' as a result of the verification of a set of validation conditions comprising at least an equation of the minimum form:
g(S, K', N2, c2, . . .)=M2 wherein,
c2 is an exchange counter controlled by B and representative of the number of values of said variable exchanged between user A and user B during said first communication session;
c. means for interrupting at the initiative of either A or B said first communication session between A and B and opening a second communication session identified by a second unique session freshness proof upon occurrence of any one of a set of session reset conditions, said set of reset conditions comprising failure of at least one of said validation conditions.

13 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/336,605Filed 9 Nov 1994
Priority: EP 934802103 Dec 1993
Granted: 7 May 1996
Term ends: Not estimatedThe source records don’t support an estimate.

Classification4 codes

H04L 9/0844
Involving Diffie-Hellman or related key agreement protocols: with user authentication or key authentication, e.g. ElGamal, MTI,…
H04L 9/0891
Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords: revocation or update of secret…
H04L 2209/80
Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication…
H04L
Digital communication