I see a problem here - given that PEM is at least trying to be a scheme
where the signatures will be (at least close to) legally binding, allowing the
recipient to decide could be a problem. Do you really want somebody being
allowed to change his mind about what you intended after the fact, especially
if a deal has gone sour and you're at each other's throats? ;)
There's no way the sender can bind the receiver to a specific set of rules
for interpreting or accepting multiple signatures. That has to be agreed
to out of band. All of the problems you suggest can happen no matter
what's in the message.
Steve
--------------------
Steve Crocker
CyberCash, Inc. Work: +1 703 620 1222
2086 Hunters Crest Way Fax: +1 703 391 2651
Vienna, VA 22181
crocker(_at_)cybercash(_dot_)com