[Mimedefang] DomainKeys

[David F. Skoll]

On Thu, 19 Aug 2004, SM wrote:

> >Furthermore, DomainKeys is trivially defeated with a replay attack.
> >Send yourself the spam through the signing server.  Now you have a signed
> >spam that you can re-mail far and wide.  Of course, you can't mutate it,
> >which might increase the effectiveness of DCC and the like, but it still
> >means you can't *really* trust a properly-signed message.

> The Received headers are also signed.  This prevents a replay attack.

Not true.  Only the Received: headers after the signature are signed.
Additional Received: headers can be added before the signature (and if
you think about it, this *must* be allowed for any mail at all to
get through.  You can't sign unknown received headers that will be
added at each hop.)

Regards,

David.