Re: [ietf-dkim] [dmarc-ietf] a slightly less kludge alternative to draft-kucherawy-dmarc-rcpts

[Michael Storz <[e-mail]>]

Am 2016-11-16 21:00, schrieb Murray S. Kucherawy:
> On Wed, Nov 16, 2016 at 11:50 PM, Michael Storz <[e-mail]>
> 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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