Cryptographic authentication with ephemeral modules

1. A method for allowing a first computer device to be authenticated by at least one second computer device during a communication session of limited duration between the first computer device and the at least one second computer device, the method comprising:

a step, for a user, of logging on said first computer device by executing a log-on software program and by introducing personal identifiers, said personal identifiers enabling the checking of the identity of said user and the accessing of a private signature key of said user;

a step, for said log-on software program, of producing:

a session identifier data Id,

a set of one or more private numbers Q 1 , Q 2 , . . . , Q m and respective public numbers G 1 , G 2 , . . . , G m , each pair of numbers (Q i , G i ) verifying either the equation G i ·Q i v ≡1 mod n or the equation G i ≡Q i v mod n, wherein m is an integer greater than or equal to 1, i is an integer between 1 and m, and wherein v is a public exponent, and wherein n is a public module equal to the product of f private prime factors designated by p 1 , . . . , p f , at least two of these prime factors being different from each other, wherein f is an integer greater than 1, said public module n being small relative to the private signature key and such that said public module n cannot be factorized by a computer having state-of-the-art computing power in a time as short as the duration of said session, and

a certificate, by signing with said private signature key at least said session identifier data Id and said public module n;

disabling the execution of the log-on software program after the log-on process is completed;

the method further comprising, at least during the first connection of said first computer device to each of said at least one second computer devices:

a step, for said user, of starting execution of a proof software program acting as a witness in a zero-knowledge authentication protocol; sending said certificate to the at least one second computer device;

a step, for said at least one second computer device, of starting execution of a verification software program acting as a verifier in said zero-knowledge authentication protocol;

a step, for said verification software program, of opening said certificate with a public key associated with said private signature key, and of extracting from this certificate the session identifier data Id and the public module n; and

a step, for the proof software program and for the verification software program of completing said zero-knowledge authentication protocol.

2. The method according to claim 1 , wherein said first computer device contains a cryptogram of said private signature key, the method further comprising a step, for said log-on software program, of deciphering said cryptogram by using said personal identifiers.

3. The method according to claim 1 , wherein a cryptogram of said private signature key is contained in a memory card held by said user, the method further comprising:

a step, for said user, of inserting said memory card in a memory card reader associated with said first computer device; and

a step, for said log-on software program, of deciphering said cryptogram by using said personal identifiers.

4. The method according to claim 1 , wherein said private signature key is located together with signature algorithms in a memory card held by said user, the method further comprising:

a step, for said user, of inserting said memory card in a memory card reader associated with said first computer device; and

a step, for said log-on software program, of producing said certificate by executing said signature algorithms with said private signature key.

5. The method according to claim 1 , wherein said zero-knowledge authentication protocol is of the Guollou-Quisquater Zero (GQ0) type.

6. The method according to claim 1 , wherein said zero-knowledge authentication protocol is of the Guollou-Quisquater One (GQ1) type authentication protocol, and wherein said public exponent v is prime with all numbers (p j −1), where the numbers p j , for j=1, . . . , f, are the prime factors of the public module n, and wherein each public number G i , where i=1, . . . , m, is obtained by applying an Rivest-Shamir-Adleman (RSA) standard signature format Red to a respective message m i , and wherein the private numbers Q i , where i=1, . . . , m, are such that Q i ≡G i s mod n, where s is a private exponent such that (sv−1) is a multiple of all numbers (p j −1) for j=1, . . . , f.

7. The method according to claim 1 , wherein said zero-knowledge authentication protocol is of the Guollou-Quisquater Two (GQ2) type authentication protocol, and wherein v=2 k , where k is a security parameter having an integer value greater than 1, and wherein each public number G i (for i=1, . . . , m) is such that G i ≡g i 2 mod n, where g i (for i=1, . . . , m) is a base number having an integer value greater than 1, and wherein the private numbers Q i , where i=1, . . . , m, are such that Q i ≡G i mod n, where s is a private exponent such that (sv−1) is a multiple of all numbers (p j −1), where the numbers p j for j=1, . . . , f, are the prime factors of public module n.

8. The method according to claim 1 , wherein the step of extracting further comprises:

extracting from this certificate at least one element of the group comprising said public exponent v and said public numbers G 1 , G 2 , . . . , G m .

9. A system comprising a first computer device and at least one second computer device, said computer devices being connected to a communications network, said system allowing the first computer device to be authenticated by the at least one second computer device during a communication session of limited duration between the first computer device and the at least one second computer device,

the first computer device comprising:

a memory on which is recorded a log-on software program to be executed by a user when logging on said first computer device by activating a control unit and by introducing personal identifiers through said control unit, said personal identifiers enabling the checking of the identity of said user and the accessing of a private signature key of said user;

first computation means, controlled by said log-on software, having means for producing:

a session identifier data Id,

a set of one or more private numbers Q 1 , Q 2 , . . . , Q m and respective public numbers G 1 , G 2 , . . . , G m , each pair of numbers (Q i ,G i ) verifying either the equation G i ·Q i ≡1 mod n or the equation G i ≡Q i v mod n, wherein m is an integer greater than or equal to 1, i is an integer between 1 and m, and wherein v is a public exponent, and wherein n is a public module equal to the product of f private prime factors designated by p 1 , . . . , p f , at least two of these prime factors being different from each other, wherein f is an integer greater than 1, said public module n being small relative to the private signature key and such that said public module n cannot be factorized by a computer having state-of-the-art computing power in a time as short as the duration of said session, and

a certificate, by signing with said private signature key, at least said session identifier data Id and said public module n;

disabling means having means for disabling the execution of the log-on software program after the log-on process is completed;

a memory on which is recorded a proof software program having instructions for controlling said first computation means, and for acting, when executed by said user at least during the first connection of said first computer device to each of said at least one second computer device by activating said control unit, as a witness in a zero-knowledge authentication protocol;

means for sending said certificate to the at least one second computer device; and

the at least one second computer device comprising:

a memory on which is recorded a verification software program having instructions for controlling second computation means, for opening said certificate with a public key associated with said private signature key, and for extracting from said certificate the session identifier data Id and the public module n, in order to act as a verifier in said zero-knowledge authentication protocol; and

launching means for launching the execution of said verification software program.

10. The system according to claim 9 , wherein:

said first computer device further comprises a cryptogram of said private signature key; and

said log-on software program has instructions for deciphering said cryptogram by using said personal identifiers.

11. The system according to claim 9 , further comprising:

a memory card held by said user and containing a cryptogram of said private signature key; and

a memory card reader associated with said first computer device for reading said memory card; and

wherein said log-on software program has instructions for deciphering said cryptogram by using said personal identifiers.

12. The system according to claim 9 , further comprising:

a memory card held by said user and containing said private signature key together with signature algorithms; and

a memory card reader associated with said first computer device for reading said memory card; and

wherein said log-on software program has instructions for producing said certificate by executing said signature algorithms with said private signature key.