Method for the unique authentication of a user by service providers

1. A computer-based method for unique authentication of a user by at least one service provider, said method including a preliminary identity federation stage of federating an identity of said user for said service provider and an identity of said user for an identity provider, wherein said preliminary identity federation stage comprises the steps of:

a computing device of the user generating a non-masked user alias for that service provider and sending said identity provider a masked user alias deduced from said user alias;

a computing device of the identity provider associating, using a processor, said masked user alias for that service provider with the identity of the user and sending elements to the user that are based on a message containing the masked user alias;

the computing device of the user unmasking the masked user alias to get the non-masked user alias;

the computing device of the user calculating a signature of a message containing the non-masked user alias and sending the service provider said message with said signature; and

a computing device of the service provider verifying said signature, authenticating the user, and associating said non-masked user alias with the user's identity for the service provider;

wherein said elements provided by the identity provider represent a partially blind signature of the message containing said masked user alias and the partially blind signature is masked.

2. A method according to claim 1 , further comprising, in the event of a request for service to the service provider after said preliminary identity federation stage, an authentication stage including the steps of:

the identity provider authenticating the user for said service provider;

the identity provider searching for the masked user alias for said service provider associated with the identity of said user for said identity provider and sending elements to the user;

the user calculating a signature of a message containing the non-masked user alias and sending the service provider said message with said signature; and

the service provider verifying said signature, recovering the user's identity for the service provider from the user alias, and providing the service requested by the user.

3. A method according to claim 1 , wherein said preliminary identity federation stage comprises the steps of:

by a computing device of the user:

receiving from the service provider, received data that is at least one of non-confidential data M and confidential data m*,

generating a user alias m of the user for that service provider, and sending said identity provider:

said non-confidential data M, when said received data comprises said non-confidential data M,

said user alias m in masked form: m masked =m·g s mod p, where g and p are public elements and s an element chosen by the user, and,

said confidential data m*, in masked form, when said received data comprises said confidential data m*;

by a computing device of the identity provider:

associating said masked user alias m masked for this service provider with the identity of the user for the identity provider,

calculating the elements m 0 =g 1 H 1 (M) ·m masked ·g 3 m 0 =g 1 H 1 (M) ·m masked ·g 3 and z 0 =m 0 x mod p, where g 1 and g 3 are public elements, x is a private key of the identity provider associated with the public key h=g x mod p, and H 1 a hashing function,

proving interactively with the user that the discrete logarithm of h to base g is equal to that of z 0 to base m 0 , and

sending the user the partially-blind signature of a message msg=M∥m for non-confidential data, and msg=M∥m∥m* for confidential data;

the method further comprising:

by the computing device of the user, unmasking said partially blind signature and sending the service provider the unmasked signature with said message msg; and

by the computing device of the service provider, verifying the signature, extracting the user alias m from the message msg, authenticating the user, and associating said unmasked user alias m with the identity of the user for the service provider.

4. A method according to claim 3 , further comprising, in the event of a request for service by the service provider after said preliminary identity federation stage, an authentication stage including the steps of:

the user receiving from the service provider at least one of non-confidential data M and confidential data m*, being authenticated by said identity provider for said service provider, and sending the identity provider said non-confidential data M, if present, and said confidential data m*, if present, in masked form;

the identity provider searching for the masked user alias m masked for this service provider associated with the identity of the user for the identity provider, calculating the elements m 0 =g 1 H 1 (M) ·m masked ·g 3 and z 0 =m 0 x mod p, where g 1 and g 3 are public elements, x is a private key of the identity provider associated with the public key h=g x mod p, and H 1 a hashing function, proving interactively with the user that the discrete logarithm of h to base g is equal to that of z 0 to base m 0 , and sending the user the partially-blind signature of a message msg=M∥m, or, where appropriate, msg=M∥m∥m*;

the user unmasking said partially-blind signature and sending the service provider the unmasked signature with said message msg; and

the service provider verifying said signature, recovering the user's identity for the service provider from the unmasked user alias m extracted from the message msg, and providing the service requested by the user.

5. A non-transitory computer-readable storage medium having a computer program recorded thereon, the computer program including instructions that cause a data processing device to execute a method according to claim 1 when executed on the data processing device.