Patent ID: 7526651
Filing Date: 2009-04-28
Classification: H04L

Abstract:
1. A method of electronic signing a message by an anonymous signatory belonging to a group of r possible signatories each having an associated public key and an associated private key in an asymmetric cryptography scheme, r being an integer greater than 1, the method comprising the following steps executed in an electronic signature device of the anonymous signatory: obtaining at least r values of variability parameters including the values of r-1 variability parameters respectively associated with the other possible signatories of the group and at least one additional parameter value; enciphering the values of the r-1 variability parameters associated with the other possible signatories of the group, by means of the respective public keys of said other possible signatories, thereby producing r-1 enciphered values respectively associated with the other possible signatories of the group; determining a complementary value which satisfies a ring equation whose variables are the message to be signed, each of the r-1 enciphered values associated with the other possible signatories of the group, each additional parameter value and said complementary value; deciphering the complementary value determined, by means of the private key of the anonymous signatory, thereby producing the value of a variability parameter associated with the anonymous signatory; and delivering an electronic signature of the message comprising the respective public keys of the r possible signatories of the group, the values of the variability parameters respectively associated with the r possible signatories of the group and each additional parameter value, wherein at least one of the r variability parameter values is an identity trace of the anonymous signatory, determined as a function of anonymity withdrawal data stored and kept secret by at least one anonymity withdrawal entity in relation with an identification of the anonymous signatory; the method further comprising: authenticating the anonymous signatory at the anonymity withdrawal entity; drawing a random value at the anonymity withdrawal entity; storing and keeping secret at least said random value and an identification of the anonymous signatory as anonymity withdrawal data at the anonymity withdrawal entity; transmitting from the anonymity withdrawal entity to the electronic signature device of the anonymous signatory an intermediate value obtained by cryptographic hashing of said random value; and generating the identity trace of the anonymous signatory at the device of the anonymous signatory as a function of the intermediate value received from the anonymity withdrawal entity.