Safari suddenly can't connect to any HTTPS site because it "can't establish a secure connection".

This is on an administrator account, not a managed account.

A different administrator account is able to use Safari with HTTPS, so must be something specific to my account, but I have no idea what.

Google Chrome has no problems connecting to HTTPS sites.

Things I have tried:

* emptied Safari's cache
* deleted Safari's preferences
* reset Safari entirely
* repaired Keychain (no errors found)
* deleted Keychain (didn't help)
* repaired permissions in Disk Utility
* rebooted
* hoped it would suddenly fix itself

All of the google results I saw suggested either repairing the Keychain (which I tried and which did not help) or were only applicable if there were "Parental Controls" involved, which doesn't apply here.

If I had to guess, I would think that wherever Safari is checking for "certificates" is somehow corrupted, but I could be wrong. I'm not even sure where to look for those - maybe `~/Library/`?