[ietf-dkim] Taking responsibility for a message

[Hector Santos]

As a follow up, here is a reason why I think Murray's definition is 
better using a twist on the MUA at ESP2 example:

      Date: Whatever
      From:  Joe  (Signed by: trustme.com. Click for Details)
      To:  Larry
      Subject: Your account is about to expire.

      Signer Details:

         Voucher:  ESP2 likes Trustme.com

         Trustme.com has authenticated the following fields:

         From:
         Date:
         To:
         List-ID:

For some stupid reason, the trustme.com signer did not include the 
subject to be hash bound to signature and we have no idea if the 
subject was modified in transit or reception.  But since the signer is 
not taking responsibility for subject alterations, the user will at 
least now some idea the subject can't be trusted.  Without the details 
like this, the user would not have any idea what could be wrong with 
this trusted message.

-- 
HLS

Hector Santos wrote:
> This is the problem with this ambiguous "responsibility" term in DKIM 
> and it becomes worst when blame or credit is distributed.
> 
> IMO, you can't have it both ways.
> 
> Sure, you are saying if unsigned parts altered or removed, then the 
> mail is still valid, everything is still A O K.  You don't care, you 
> are not responsible for these unsigned parts and most important of 
> all, the message is trusted if the signer is vouched for some way, 
> even if all unsigned parts is removed or altered!
> 
> But that can only be true specifically because of the hash bound PARTS 
> you signed and took responsibility for.  So in this vain, Murray 
> definition sound to be logical and technically correct:
> 
>      The signer is only accepting responsibility for the authenticity
>      of the specific parts it bound to the signature.
> 
> That is much clear than saying:
> 
>      "The signer takes some responsibility for the message."
> 
> when it doesn't care for what has changed in the message payload as it 
> travels.
> 
> Another perspective with be a DKIM ready MUA display.
> 
> The MUA at ESP1 displays:
> 
>      Date: Whatever
>      From:  Joe
>      To:  Larry
>      Subject: Bananas
>      Signed by: trustme.com
> 
> then I can see your viewpoint better.  There is something about
> the signer that it is claiming some responsibility for the message.
> 
> But the MUA at ESP2 displays:
> 
>      Date: Whatever
>      From:  Joe  (Signed by: trustme.com. Click for Details)
>      To:  Larry
>      Subject: Bananas
> 
>      Signer Details:
> 
>         Voucher:  ESP2 likes Trustme.com
> 
>         Trustme.com has authenticated the following fields:
> 
>         From:
>         Date:
>         Subject:
>         To:
>         List-ID:
> 
> Then Murray is again correct.
>