On 4/11/2025 1:03 PM, Richard Clayton wrote:
> There has been a continuing need to be able to add/replace crypto
algorithms.
> So the dexterity is a legitimate need, but is not new. And it is
already
> supported in DKIM. And, really, it has nothing to do with the
status of P-Q
> concerns.
it is mainly about post-quantum if we write MUST for both RSA and EC
_and_ enough people use EC to shame the people who ignore that MUST :-)
Since DKIM already provides the desired 'dexterity', this is another
example of needing a BCP and not a protocol revision.
>> 4.9. Reducing crypto-calculations
>>
>> Experience at large mailbox providers is that incoming messages can
>> have large numbers of DKIM signatures all of which need to be
>> checked.
> But, do they really /all/ have to be checked? Seriously, why can't
there be
> some selectivity?
They all need to be checked because of feedback loops
Please explain.
>> For DKIM2, in the common case where email has not been
>> altered by earlier hops, it will only be necessary to check the
first
>> DKIM2 signature, the one applied by the previous hop and, if
>> "feedback" is to be provided, the signatures of any entities that
>> have requested feedback.
> huh? This does not seem at all obvious.
nevertheless I believe it to be a correct statement ... which other
signatures do you think need to be checked and to what purpose ?
Your text makes an assertion of fact. I invited you to explain that
assertion.
I continue that invitation.
> Also, it is not obvious that the current use of DKIM requires
checking all the
> signatures. Please explain why.
see above
see above.
>> If DKIM-replay is felt to be an issue (and some providers will
detect
>> this by identifying non-unique signatures)
> Non-unique signatures? Since I am quite sure this does not mean two
different
> signatures that produce the same value, what does this mean and how
is it a
> problem?
I discuss DKIM-replay in another of these emails so I will not repeat
that commentary here
So far, I haven't seen any explanation of the rather curious term
'non-unique signature', yet that was what I asked about.
>> then more DKIM2 headers
>> may need to be processed to establish the veracity of an alleged
>> forwarding path. Additionally any attempt to do forensics or to
>> assign reputation to intermediates will require more signatures
to be
>> checked.
> What is meant by forwarding path?
the path taken by the email to arrive at the current machine
> How is it specified?
in the DKIM2 headers
> What does it me to
> 'establish the veracity' of it?
is there a correlation between RCPT-TO:<n-1> and MAIL-FROM:<n> ?
Since SMTP does not require any correlation between these, it appears
you are proposing a change to SMTP.
note that systems which know there is not a correlation can generate a
DKIM2 header to show the correlation -- the entity that signs that DKIM2
header will be taking some responsibility (to coin a phrase) for that
> As for needing to check signatures by intermediaries, before performing
> reputation analysis... yup? What is the problem?
Interesting this did not garner a response.
d/
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net
bluesky: @dcrocker.bsky.social
mast: @[email protected]
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