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SSL certificates and MD5 collisions

SSL certificates and MD5 collisions

Posted Jan 15, 2009 9:04 UTC (Thu) by HenrikH (subscriber, #31152)
Parent article: SSL certificates and MD5 collisions

While not a fix for the problem as such, I think it would be good if the browser (say Firefox) did store the certificate's signature together with the URL in a database (for example the same database used for the address bra history).

That way it could be discovered when a site suddenly changes it's certificate. Now this will happen for legit reasons (some time before expiry date) but could also be a sign that some one is trying to forge the certificate.

Perhaps with more explicit warnings if the change was from say a certificate with extra validation (aka the green address bar certs) to a url only certificate.

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SSL certificates and MD5 collisions

Posted Jan 15, 2009 9:25 UTC (Thu) by (subscriber, #26289) [Link]

I have been wishing for such a feature for year. The way OpenSSH does it is perfect. I do trust my personnal certificate hash storage more than CAs, their search for profit prevents accurate verification of identities.

The probability that the site I visit was not showing the right certificate the first time I connected to it is very low and comparing the hash is adding a really useful security layer. Defense in depth.

SSL certificates and MD5 collisions

Posted Jan 15, 2009 15:06 UTC (Thu) by iabervon (subscriber, #722) [Link]

Beyond the profit motive, privacy concerns and scalability issues prevent CAs from really verifying identities usefully. In order for them to give useful verification, they'd have to not issue certificates to anyone other than my bank and credit card company; otherwise, there's the risk that some other entity will have a confusing site that makes me think that it's my bank when it is actually something else. Since the CA doesn't know what bank I use, and since it wants to be useful to customers of other banks, this is impossible.

SSL certificates and MD5 collisions

Posted Jan 15, 2009 19:02 UTC (Thu) by bronson (subscriber, #4806) [Link]

Ya, great. Now a simple DNS spoof/poisoning can replace all your browser certs with evil ones.

Beware the cure that's worse than the disease.

SSL certificates and MD5 collisions

Posted Jan 15, 2009 20:54 UTC (Thu) by HenrikH (subscriber, #31152) [Link]

Exactly how could your scenario replace my browser certs with evil ones when all my proposal does is to add an extra layer of verification (that the certificate has been changed since my last visit) ?

SSL certificates and MD5 collisions

Posted Jan 17, 2009 19:55 UTC (Sat) by bronson (subscriber, #4806) [Link]

Sorry, I misread your suggestion. I thought you were suggesting a CRL-like behavior. If you're just talking about adding an SSH-like warning, and not manipulating or revoking the certificates on the browser itself, then I take back what I said.

Of course, the SSH warning has been shown to be fairly ineffective in the real world. And that's with sysadmins who should know better! What about regular people? When presented a dialog box saying "The certificate for Chase Bailout Bank has changed! Do you want to continue?" I would guess that 99 out of 100 of them would simply click "Yes."

But, I agree, it wouldn't hurt.

SSL certificates and MD5 collisions

Posted Jan 20, 2009 9:33 UTC (Tue) by HenrikH (subscriber, #31152) [Link]

That is exactly my suggestion, to add a SSH-like warning. Agreed that not many people would benefit from it, but I know that I would :-)

SSL certificates and MD5 collisions

Posted Jan 19, 2009 14:44 UTC (Mon) by TRS-80 (subscriber, #1804) [Link]

Perspectives (LWN discussion) sort of does what you want, except storing the cert on public "network notary servers".

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