ietf-smime
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RE: Is 7bit restriction to signature practical?

1997-09-12 13:33:12
On Thursday, September 11, 1997 7:49 PM, Kazu Yamamoto
[SMTP:Kazu(_at_)Mew(_dot_)org] wrote:
Do other UA implementors agree that this MIME requirement is
reasonable and practical to you?

I personally think it's reasonable, just because of the reality of the
situation.  I don't think it's practical, but practicality is a
secondary goal to compatibility which would be sacrificed in this
particular case.

The fact is that a message will have to travel over an arbitrary path to
its destination.  When sending a signed message, all of the things along
that path need to be able to pass the signed part along completely
intact without modification (in order for the signature to be valid).
In a pure Internet environment, it seems that you might encounter 8bit
friendly and 8bit, uh, unfriendly hops.  If the original data is
multipart/signed with 8bit inside, an intermediate 7bit-only hop can do
a bunch of things:

1. Puke.  Forget to analyze the incoming content and it ends up broken
when it comes out (8bit data over 7bit transport)
2. Convert the offending 8bit stuff to QP or some other effectively 7bit
CTE (breaking the signature)
3. Understand that the message is multipart/signed, and bounce it
because it knows that it will be smashing the signature in the event
that it changes the CTE for any of the content.
4. Perform step 2 and remove the signature.

I think that 1 and 2 are the current mode of operation.  Ned has
consistently argued that we should put some language somewhere to
address this, since the lack of MTA / gateway language is what is
causing some of the current problems (including the one you are pointing
out, I believe) with multipart/signed.  I believe that discussing this
more is a good idea, despite any previous comments that may have
indicated the contrary.

So the bottom line on how to fix this is to come up with gateway / MTA
specific language about how to deal with multipart/signed.

Blake
--
Blake C. Ramsdell
Worldtalk Corporation
For current info, check http://www.deming.com/users/blaker
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