On Jul 4, 2006, at 10:22 PM, Jim Fenton wrote:
Paul Hoffman wrote:
At 10:40 AM +0100 7/4/06, Stephen Farrell wrote:
#3 1.1, 2nd set of bullets. dkim *does* require a ttp - the DNS.
Better to say that dkim requires no *new* ttp.
I don't see DNS as a "third party" in the same sense as a CA for
certs. Yes, DNS has to work, but it isn't a third party (unless
you
want to count the root servers, I suppose). By this logic, we
should also include the multiple third parties that run the routers
and all the rest of the infrastructure.
In my little PKI-riddled mind, the DNS is a TTP since it supplies
the
public keys and if/when DNSSEC were used, it starts to look quite
like
a PKI. The routers etc. won't ever really be supplying signed key
records. But if no-one else thinks the same, leaving as-is if of
course
right.
My brain has the same affliction as Stephen's in this department. The
keys have to be distributed somehow. The keys are not inherently
trusted. DKIM users trust the keys they get from the DNS. The DNS is
the trusted third party who hands out keys.
I'm also with Stephen on this. I think it helps our credibility to
acknowledge the dependency on DNS, although the threat document has
already spelled that out in some detail.
DKIM generally represents a domain wide entity. A trusted third
party (TTP) establishes trust between two parties when both trust the
third party. For DKIM, the TTP would be the signing domain verified
by DNS. To be a TTP, the signing domain would need to be known and
trusted by verifier (the second party) for signing email-addresses of
different domains (the first party) or this does not represent three
parties. DNSSEC, except making a stronger verification of the
signing domain, does not alter this model. Unless DKIM is expected
to be commonly used with third-party signatures, it seems
inappropriate to describe DNS as a TTP, nor does DNS represent a
discrete entity or party.
-Doug
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