[145547] in cryptography@c2.net mail archive
Re: Five Theses on Security Protocols
daemon@ATHENA.MIT.EDU (Guus Sliepen)
Sun Aug 1 13:02:49 2010
Date: Sun, 1 Aug 2010 15:07:46 +0200
From: Guus Sliepen <guus@sliepen.org>
To: cryptography@metzdowd.com
Mail-Followup-To: Guus Sliepen <guus@sliepen.org>,
cryptography@metzdowd.com
In-Reply-To: <E1OfWb5-0003Xm-4p@wintermute02.cs.auckland.ac.nz>
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On Sun, Aug 01, 2010 at 11:20:51PM +1200, Peter Gutmann wrote:
> >But, if you query an online database, how do you authenticate its answer=
? If
> >you use a key for that or SSL certificate, I see a chicken-and-egg probl=
em.
>=20
> What's your threat model?
My threat model is practice.
I assume Perry assumed that you have some pre-established trust relationship
with the online database. However, I do not see myself having much of those.
Yes, my browser comes preloaded with a set of root certificates, but Verisi=
gn
is as much a third party to me as any SSL protected website I want to visit.
Anyway, suppose we do all trust Verisign. Then everybody needs its public k=
ey
on their computers to safely communicate with it. How is this public key
distributed? Just like those preloaded root certs in the browser? What if t=
heir
key gets compromised? How do we revoke that key and get a new one? We still
have all the same problems with the public key of our root of trust as we h=
ave
with long-lived certificates. Perry says we should do online checks in such=
a
case. So which online database can tell us if Verisign's public key is still
good? Do we need multiple trusted online databases who can vouch for each
other, and hope not all of them fail simultaneously?
Another issue with online verification is the increase in traffic. Would
Verisign like it if they get queried for a significant fraction of all the =
SSL
connections that are made by all users in the world?
--=20
Met vriendelijke groet / with kind regards,
Guus Sliepen <guus@sliepen.org>
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