a first step of calculating, at first calculation means of a trusted authority, a pair of asymmetric keys common to the members of the group and comprising a common public key and a common private key;

a second step of calculating, at the first calculation means of the trusted authority, a group public key associated with the members of the group;

a third step of calculating, during an interaction between the calculation means of the trusted authority and the calculation means of the member, a group private key for each member of the group and storing the private key in the storage means of the each member, each group private key being associated with the group public key and being different for each member of the group;

a fourth step of determining, at the first calculation means of the trusted authority, as many symmetrical secret keys as there are members of the group; and

a fifth step of encrypting, at the first calculation means of the trusted authority, the common private key using each of the symmetrical secret keys to obtain as many encrypted forms of the common private key as there are non-revoked members;

on each revocation of a member from the group, the method further comprising:

a sixth step of modifying, at the first calculation means of the trusted authority, the pair of asymmetric keys common to the group to create an up-to-date common public key and an up-to-date common private key;

a seventh step of encrypting, at the first calculation means of the trusted authority, the up-to-date common private key using each of the symmetrical secret keys to obtain as many encrypted forms of the up-to-date common private key as there are non-revoked members; and

when a non-revoked group member anonymously signs a message to be sent to an addressee, the method further comprising:

an eighth step of updating the common private key stored in the storage means of the signing member only if one encrypted value of the up-to-date common private key may be decrypted using the symmetrical secret key stored in the storage means of the signing member;

a ninth step of calculating, at the calculation means of the signing member, an anonymous signature of the message using the group private key for the signing member; and

a tenth step of calculating, at the calculation means of the signing member, an additional signature of a combination comprising the message and the anonymous signature using the up-to-date common private key of the signing member;

wherein the group is constituted at a date t1 and the method further comprises:

during the first step associating, at the first calculation means, the common private key with an updated date equal to t1; and

during the third step storing, at the storage means of each member, the updated date of the common private key;

wherein at the time of each revocation within the group at a date t2:

during the sixth step modifying, at the first calculation means of the trusted authority, the updated date to determine an updated date equal to the date t2; and

wherein on each anonymous signing by the member of the group of the message to be sent to the addressee:

during the eighth step, the common private key stored in the storage means of the signing member is updated only if the updated date in the storage means of the signing member is also different from the updated date of the up-to-date common private key updated by the first calculation mean.