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Re: My $0.02 re MIME / secure mail

1993-11-02 08:34:29
(1) They are obviously incomplete since they only provide for PEM
secured messages and not for PGP secured messages.  The format should
be general enough that one could send out a message with a PEM
signature and a PGP signature (and a DSS signature...) and be able to
handle the more ugly and hopefully less common case where you need
more than one cyphertext version due to different algorithms, etc.

The incompleteness of the specification in this regard is intentional.
It is not our purpose to specify how PGP would fit into MIME hee.

However, your implicit assumption here seems to be that the structure is not
general enough to handle PGP. This is in fact untrue. As a matter of fact, it
should be possible to have a PEM and a PGP signature on the same document
without duplicating any content. (The encryption case requires repeated content
for obvious reasons.)

Work is now underway to clarify how these things are done. While this work
will probably stop short of specifying the handling of PGP, it sould
make it possible to address this issue with a relatively simple additional
specification. (This presupposes that PGP will elect to use this approach to
MIME encapsulation, which may not be the way the PGP community decides
to do it.)

(2) Soon, people are going to notice that when they reply to a message
and want to include an extract, they would like to have the extract
authenticated.  The only way I can see to do this is to include all of
the message responded to, with its signature/certificates, and provide
a MIME body part that is in effect a window into this message.  (Most
commonly to text but you might as well have a way to window into sound
or an image, etc.)  This also has the nice effect that a reader could
be provided with a way to see all of the original message being
replied to to see that the extract was/was-not out of context.  You
don't really want this "extract window" thing to be a multi-part with
the thing windowed into as the 2nd part or something (at least I don't
think so) as it is very common to have multiple windows into the same
base message.  You want it identified by id and have it been somewhere
else with presentation to the reader normally surpressed.

Well, it isn't quite this one-sided. MIME-PEM supports selective enhancement of
parts of a message. The price you pay for this, however, is the loss of overall
message integrity. The original sender could secure each section of the message
separately as well as secure the message as a whole, but the overhead involved
would be pretty big.

The pointer scheme you propose is another reasonable approach. Please note that
work is also underway to specify how internal references inside a message will
work. Once this is done it should be a relatively trivial matter to define some
very simple type of document that uses pointers to secured parts to build up a
composite response. 

                                        Ned

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