receiving a validation message from a merchant party via an input port of a computer, the validation message comprising a proof signature produced by a customer party and an encrypted payment message, the proof signature being derived from a zero-knowledge proof 1) of knowledge of a customer secret key, a customer certificate, and at least one customer attribute, 2) that the encrypted payment message encrypts said customer attribute, and 3) that said customer certificate is valid and is related to said customer secret key, thereby allowing said customer secret key, said customer certificate, and said at least one customer attribute to remain anonymous to said merchant party;

verifying, by said computer, a validity of the proof signature based on an issuing public key, a verification public key, and the encrypted payment message;

decrypting, by said computer, at least part of the encrypted payment message based on a verification secret key corresponding to the verification public key, thereby obtaining a customer information related to the at least one customer attribute; and

in an event of the validity of the proof signature, the computer using the obtained customer information for initializing an authentication of the payment, and, in an event the proof siginature is not valid, the computer provides an indication that the proof siginature was not valid.