Re: [ietf-822] A permission to re-sign header

[Paul Smith <[e-mail]>]

On 22/04/2014 11:15, Alessandro Vesely wrote:
> On Tue 22/Apr/2014 04:58:21 +0200 Ned Freed wrote:
>>> On Sat, Apr 19, 2014 at 09:05:23AM -0400, Michael Richardson wrote:
>>> There are mailing lists that want to "fix" broken messages, yes, but
>>> if we need to provide end-to-end assurance that the message really
>>> came from the originator, disallowing this behavior so that things
>>> like S/MIME and PGP signatures don't get broken might be an
>>> engineering tradeoff that we might have to make.
>> That's possible, but then you run into other problems. Take the issue
>> of adding a disclaimer. You can certainly do this without damaging
>> the S/MIME signature by converting a MIME structure of:
>>
>>     multipart/signed
>>       text/html
>>       application/signature-whatever
>>
>> to:
>>
>>     multipart/mixed
>>       multipart/signed
>>         text/html
>>         application/signature-whatever
>>       text/plain - disclaimer
>>
>> But then you have to take into account how this gets displayed, and what
>> it means when it is displayed.
> That alters the content-type and the very beginning of the message body.
> The result may be more difficult to display/interpret than a signed
> attachment.
>
> For a related trifle, no PGP or S/MIME signatures could have pointed out
> that I altered a few bits in the text quoted above, attributed to Ned.
> Did I thus break authentication, non-repudiation, or integrity?
>
I know people think I'm wrong, but I think it needs to be looked at a 
different way. As a recipient, I don't want 'proof' that this message 
came from Alessandro, I want 'proof' that it came from the 
[e-mail] mailing list.

I have chosen to trust that mailing list. What I don't want is to 
receive messages pretending to be from that mailing list, but not really 
coming from it.

Then, because I trust that mailing list, I trust that it has done what 
it can to be sure that messages which claim to come from Alessandro 
really did.

So, I see the mailing list as being the 'final' recipient of the message 
from Alessandro. Then, the mailing list sent a new message to me, 
containing (to a reasonable degree) the content of the message which 
Alessandro sent. I did NOT receive the message from Alessandro, I 
received the 'essence' of that message, in a new message from the 
mailing list. The mailing list is not simply a forwarder/redistribution 
list, it is an entity in its own right, which receives and sends 
messages. (If you want, you could get the mailing list to include the 
original message as an attachment, so signatures etc can be validated in 
that).

Once you think of it in that way, then the problems become a lot fewer, 
IMHO. I don't really see how it can work any other way, without 
castrating the mailing list system so it just becomes a dumb 
distribution system.

-


Paul Smith Computer Services
Tel: [phone]
Vat No: GB 685 6987 53