The present invention discloses a method and system for maintaining privacy for transactions performable by a user device having a security module with a privacy certification authority and a verifier. The system comprises an issuer providing an issuer public key PKI; a user device having a security module for generating a first set of attestation-signature values DAA1; a privacy certification authority computer for providing an authority public key PKPCA and issuing second attestation values AV2; and a verification computer for checking the validity of the first set of attestation signature values DAA1 with the issuer public key PKI and the validity of a second set of attestation-signature values DAA2 with the authority public key PKPCA, the second set of attestation-signature values DAA2 being derivable by the user device 20 from the second attestation values AV2, wherein it is verifiable that the two sets of attestation-signature values DAA1, DAA2 relate to the user device.