Paul Hoffman <paul(_dot_)hoffman(_at_)domain-assurance(_dot_)org> writes:
At 3:43 PM -0800 12/26/06, EKR wrote:
I don't know what's being proposed here, but as a technical matter
it's not really the case that you can't individually insulate each
header from breakage without doing a separate signature for each
one. Rather, you could simply include digests for the header value in
the header specification, i.e.,
DKIM-Signature: a=rsa-sha256; d=example.net; s=brisbane;
c=simple; q=dns/txt; i=(_at_)eng(_dot_)example(_dot_)net;
t=1117574938; x=1118006938;
h=from=<digest-value>:to=<digest-value>:subject-<digest-value>:date=<digest-value>;
...
This is actually less information than the z= tag, which says what the
value was when signed.
Yes, that's true, so even without this optimization it's not true
that you need to a separate signature for each header.
That said, this representation is more compact, so it's a tradeoff.
It also doesn't come with this restriction:
Verifiers MUST NOT use the header field names or copied values
for checking the signature in any way. Copied header field
values are for diagnostic use only.
But of course that restriction could be relaxed.
-Ekr
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