signature construct (was: Re: [ietf-dkim] DKIM BOF -- draft charter and agenda)

[william(at)elan.net]

On Sat, 15 Oct 2005, Earl Hood wrote:

> On October 14, 2005 at 12:08, Stephen Farrell wrote:
>
>> PS: Just so's I can reconstruct it for myself later, the construct
>> might end up something like:
>>    body-hash = Hash1(nonce, body)
>>    sig-bits  = Private-key(Hash2(nonce,header-stuff, body-hash))
>
> Actually the "data" hash would be more like:
>
>  data-hash = Hash1(nonce, header-stuff, body)
>  sig-bits  = Private-key(Hash2(nonce, DKIM-Signature-field))
>
> I.e. The digital signature is only on the DKIM-Signature field,
> nothing else.

For comparison META Signatures is something like:
  data-hash = hash1(nonce, some-headers, body-part)
  ; body-part can be particular mime part (or several) or entire message body
  ; some headers is optional and typically include only Content-* fields
  sig-bits = Private-key(hash2(nonce, meta-parts, data-hash, header-stuff))
  ; where meta-parts is META-Signature field with sig segment cut out

META-Signature design itself allows for inclusion of header fields in
either way listed in previous email (together with body hash or together 
with signature itself) but I obviously prefer inclusion with signature.

-- 
William Leibzon
Elan Networks
william at elan.net