Re: [dmarc-ietf] third party authorization, not, was non-mailing list

[Doug Foster <[e-mail]>]

Are the weak signatures vulnerable to a replay attack?    I thought that one of the reasons that DKIM signatures included the whole body was to prevent the signature from being reused.

 

DF

 

From: dmarc [mailto:[e-mail]] On Behalf Of Dotzero
Sent: Tuesday, August 25, 2020 1:51 PM
To: John R Levine
Cc: IETF DMARC WG
Subject: Re: [dmarc-ietf] third party authorization, not, was non-mailing list

 

 

 

On Tue, Aug 25, 2020 at 12:22 PM John R Levine <[e-mail]> wrote:

On Tue, 25 Aug 2020, Dotzero wrote:
>> https://tools.ietf.org/html/draft-levine-dkim-conditional-00?

> Under my concept, all mail would still be signed in full. The weak
> signature would be in addition to the full signature and the intermediary
> would be expected to sign in full as well. If the original full signature
> is broken you are left with the original "weak signature" which authorizes
> the intermediary and the full signature of the intermediary.

Take another look at my old draft.  Sounds like exactly the same plan.

 

I will. 


> I would expect there to be multiple potential approaches to identifying
> acceptable intermediaries.

The harder part is to decide which intermediary gets to re-sign which 
message at the time you apply the weak signature.

 

It would have be the domain in the "To" field.  It wouldn't work with random unknown intermediaries. It would address the MLM issue as long as the MLM domain is the same as the "To" domain when the message was originally sent. It could also presumably work for vanity domains if they DKIM sign. It wouldn't work for forwards on the receiver side that the sender is unaware of.

 

Michael Hammer