The second solution is also straightforward (see
Figure 6). It consists in sending to the card all
elements of the ``black list'' one by one, each of them signed by
the group manager. It is yet necessary to add a revocation
number (a sequence number: number 1 corresponds to the first
revoked member, etc.) to prevent some attacks (for example
addition or substitution of some identifiers). In addition, GM
signs the date of his updating of the ``black list'' and
the number of revoked members.