Re: DK and mailinglists

[Murray S. K. <ms...@se...>]

SM wrote:
> I meant to say that the Received: headers are reordered during 
> canonicalization.  I didn't mean omitted from the signature.

Thanks for your help with tracking this down.  The issue appears to be the 
injection of a message with duplicate but separated headers.  For example, a 
dummy message like so:

	Received: data 1
	Received: data 2
	From: ms...@se...
	To: sa...@se...
	Subject: test

	test blah foo

...will sign and verify just fine.  If you add "-H" (which adds the "h=" header 
order tag to the signature), you can even tinker with the order for the most 
part and it will continue to work.  However, if you insert any of those headers 
between the two Received: headers, the signatures begin to fail.

The reason for this appears to be that the header sorting and canonicalizing 
code anticipates your use of "-H" and thus groups like headers when 
canonicalizing.  As such, the above instance will always work, but without "-H" 
this ordering will always fail:

	Received: data 1
	From: ms...@se...
	Received: data 2
	To: sa...@se...
	Subject: test

	test blah foo

If you don't use "-H", the verifier won't know you did the grouping when signing 
and will replay the headers in their original order.  So the sender's canonical 
form is what's above, but the verifier's is what's below, and you're sunk 
because they don't match.

I'll open this as a bug and get it fixed as soon as I can.