[ietf-dkim] one more comment I forgot...

[Douglas Otis]

On Jan 11, 2006, at 11:19 AM, Michael Thomas wrote:

> Stephen Farrell wrote:
>>
>> Yes, but mucking up a signature is already covered in the draft  
>> whereas totally ditching one isn't.
>>
>> (Perhaps "forwarder" wasn't the right term - if not, mea culpa.)
>
> From a threat perspective, the two are identical, right?

The term mediator may have been better.  Removal of a signature  
within that role may also introduce a new signature by the mediator.   
In this case, a signature has been removed and replaced with a  
different signature.  In the case of replacement, the results should  
not be identical.  Being able to define the role of the signer may  
help resolve handling issues.

> If a receiver in any way treats broken signatures different than  
> missing signatures, an attacker can exploit the preferable  
> treatment trivially.

This was not about a broken signature, but a deliberately removed  
signature.  Once there is a greater concern related to the overhead  
associated with handling multiple signatures, how this gets handled  
will have greater importance.  A bad actor could trivially increase  
recipient burdens by introducing multiple signatures with various  
body lengths and multiple From addresses.  Unfortunately, due to the  
authorization scheme, this may also become a common practice by  
legitimate mediators. : (

-Doug