A variant of the first solution consists in replacing the ``black list'' by a much shorter digest, so that the verification step becomes in average much faster. If the output of this step is ``no'', then we are sure that the member is not revoked and the card accepts to sign. However, if the output is ``yes'' then we cannot definitely conclude and the whole ``black list'' should be requested for a complete verification. We now briefly describe in the following subsection a possible way of achieving a compression of this kind.