Hi,
[ASRG removed, since I cannot see even a little bit how this is
on-topic there. But if you think it is, feel free to republish this
as you like.]
On Tue, Jun 09, 2009 at 08:54:48AM +0900, Masataka Ohta wrote:
As has been discussed in the thread, DNSSEC is NOT a protection
against cache poisoning, because caches poisoned with forged
certificate breaks the security.
To beat the stain on the ground that betokens the long-since-passed
equine presence, you haven't answered the question, posed to you
several times, how this poison-with-forged-certificate is supposed to
work.
If I have a validating resolver, and I get data from a poisoned cache,
then I attempt to validate the signature over that data, checking
the chain of signatures from that data all the way back to some trust
anchor I have configured. Therefore, in order to poison a cache with
a forged certificate, one of two things has to have happened:
1. The forger managed to forge keys and inject them in the
poisoned cache such that one of those keys will be valid according
to the trust anchor I have installed. Is this the threat you
claim? If so, and assuming you're not saying that the crypto is
weak (in which case we have way bigger problems than forged DNS
data), that just seems to be a claim that the signing procedures
can be subverted. And yes, of course, a security system is
possibly subverted by poor operation. I'm not sure what the
surprise is supposed to be here. You can argue just as easily
that the DNS is badly secured because it's possible to convince a
registrar to publish the wrong data for a domain (a problem we've
certainly seen in action more than once). It is indeed possible
to get bad data into the system, and DNSSEC doesn't completely
protect against such bad data coming in; but that is no criticism
of DNSSEC.
2. The forger managed to forge data that is not validatable in a
chain from any trust anchor I have, and managed to convince me to
trust it anyway. If this is the threat you claim, I want to know
how this works. If you're right, then DNSSEC is indeed completely
broken. We need to know that now, before more deployment goes on.
If neither of (1) or (2) happens, then my attempt to validate the data
will fail, marking the data bogus. It is true that this is a vector
for denial of service: I won't connect to a site with invalid DNS
data. I'm having a hard time coming up with a reason why that is
worse than "I go to the site controlled by Dr Evil."
Best regards,
Andrew
--
Andrew Sullivan
ajs(_at_)shinkuro(_dot_)com
Shinkuro, Inc.
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