Am 2016-11-16 21:00, schrieb Murray S. Kucherawy:
On Wed, Nov 16, 2016 at 11:50 PM, Michael Storz
<Michael(_dot_)Storz(_at_)lrz(_dot_)de>
wrote:
Ok, I see you have removed the hashing of the recipient together
with the email itself. But how do you prevent a replay attack, if
the new tag is not bound to the email and signed with the DKIM-key
(that's how I read 4.1.4)? The spammer could remove the tag or
provide his own tag with the new recipient before resending the
email.
The signature signs itself, so removing or changing the tag
invalidates the signature. Have a look at RFC6376, Sections 3.5 and
5.1.
-MSK
Thanks, I see. That means the recipient is bound to the message and an
attacker cannot delete or change the new tags. Great solution, I like
it, though I do not like the consequences when this extension will go
into production.
Michael
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