At 5:57 PM 12/27/94, Steve Kent wrote:
Steve,
One of my principal objections to the current MIME-PEM
proposal is that it has the flavor of "there is a baisc capability to
do a wide range of things; we have defined one example; other examples
may come along 9or we may already have them in mind but we aren't
telling you) and we'll figure out what the semantics is when we get
there (or when we decide to tell you)." The idea that the semantics
of multiple signatures applied to an object is up to the recipient
stikes me as complete foolishness! The signer(s) should have a means
of expressing the sematics to verifiers in an unabmiguous fashion, so
that two different verifiers don't interpret the signatures
differently.
Steve
Let me try to say this a bit differently. If A sends B a message and it
contains multiple signatures. What is B supposed to do? There has to be
some sort of agreement beforehand as to what the existence of multiple
signatures means and what actions are to be taken. That agreement cannot
be transmitted within the check. Therefore, it's something the receiver
already knows.
It's probably worth working through various cases to see the details, but I
don't see any way for the meaning of multiple signatures to be specified
within the message unless it's to choose from a pre-agreed roster of such
meanings or is the consequence of the meanings of the individual
signatures. (Nested signatures fall into the latter camp.)
You say "[t]he signer(s) should have a means of expressing the semantics to
verifiers in an unambiguous fashion so that two different verifiers don't
interpret the signatures differently." Implicit in this statement is the
idea that there might indeed be two or more different ways for the
signatures to be interpreted, and thus you are also saying the signer(s)
say(s) which of the different ways applies. Can you give an example of how
it can be menaingful for the signer(s) to specify the meaning of the
signatures?
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