At 05:17 18-06-2008, John Levine wrote:
[ not about ADSP, about DKIM ]
An acquaintance points out that one could prepend an extra From: or
Subject: header to a DKIM signed message, which wouldn't break the
signature, but would often be displayed by MUAs which show the new one
rather than the old one. Needless to say, that weakens the practical
benefit of DKIM for people with MUAs like that.
Yes. As you pointed out, the message would no longer be valid
according to 2822.
My theory is that DKIM only applies to valid 2822 messages, and it's not a
substitute for a sanity check for all the screwy things one can send in a
non-conformant message. Perhaps it would be a good idea someday to
collect experience and advice into an implmentation guide, but other
than that, it's not our problem. Agreed?
There is an implementation note about signing all end-user visible
header fields. The topic of multiple From headers came up during a
discussion about a DK implementation. It was suggested not to sign
such messages. If I recall correctly, the test was also done in the
DKIM implementation. At the verification stage, it's better to do a
sanity check on the headers before verifying the signature and flag
non-conformant messages.
Regards,
-sm
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