On Sat, 16 Aug 2008, Ted Lemon wrote:
> On Aug 16, 2008, at 9:35 PM, Dean Anderson wrote:
> > - If Mal cracks someone else's server, that server still doesn't have
> > the bank's certificate, and won't have the bank's dns domain, either.
> > So the browser should think that it got the wrong certificate.
>
> No, that wasn't my point. My point is that sometimes browsers will
> warn you if you submit a form to a non-SSL server. So an attacker
> can get rid of that warning by suborning an SSL server and directing
> your response toward it. You won't get a warning that your data is
> being submitted over an insecure link, because it's not. The link is
> perfectly secure - the problem is that it's the wrong link, and
> someone's listening on the other end who shouldn't be.
Anytime the browser takes a certificate that is not user-checkable as
being both secure and trusted, there will be problems.
> So any attack that can make things not look funny is a valuable
> attack. And the Kaminsky attack is such an attack. You're right that
> it's not the only one, but eliminating it still has appreciable value.
One can live with things that are untrustworthy, so long as you know
they are untrustworthy and takes the appropriate steps to avoid placing
trust decision on untrustworthy information. SSL/TLS certificate
procedures the appropriate steps to obtain secure and trusted
communication.
Changing DNS doesn't eliminate the attack of misplaced trust. It merely
eliminates one method we know of for accomplishing the attack, at great
expense and great risk, I might add. Addressing the misplaced trust
attack in the wrong place incorrectly signals to users/browsers that
they don't need to check the certificates for trustworthiness.
DNS spoofing isn't the only way to accomplish a misplaced trust attack.
Cross site scripting and javascript viruses are another way.
Cryptographic verification just proves the CA issued the certificate.
Checking that the verified identity is one we trust is what ensures
trustworthiness. The combination of both checks the only thing that
ensures trustworthiness. One can't eliminate either check and remain
trustworthy. Every certificate that a browser uses for trustworthiness
has to be both verified cryptographically and checked by the user for
trust. Multi-site secure operations have to either have multiple
certificate checks, or depend on a private CA whose certificates are
always trusted.
--Dean
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