A few days ago, all my disk images, including my backups stopped mounting… flat. Once double-clicked, hdiutil complained about an authentication error and refused to go any further. Had I been bitten by the ghost of the FileVault bug? Nope, luckily!

Googling around for information did not help much. Even the hdiutil man pages referred only vaguely to a certificate-related issue and suggested adding a flag to bypass checks, which didn’t help much. I had already started trying to back everything up and to start fresh when I noticed the problem was much more widespread than I though: not only was I unable to mount my existing images, I couldn’t, no matter how hard I tried, create new ones…

Clearly, the problem was different than what I had originally thought. If I was unable to create new images chances that we were dealing with corruption were extremely slim. And yet… After much green tea, the word Authentication seemed to whisper something to me: look into the Keychain structure! Of course!

Keychain First Aid was of no help, which I have to say is rather uncommon. According to it, everything was peachy under the sun when it clearly wasn’t. Just for kicks, I proceeded to quit Keychain Access, rename my Login keychain and use Keychain First Aid again to re-create one and smooth problems out.

Guess what? Everything was now able to mount normally, even my old backups. What’s especially troubling to me is that there were no other issues whatsoever with the Keychain infrastructure and that I never used my login keychain to store any disk image passwords…

Yet, here laid the solution: replacing a stale login Keychain with something a tad healthier.

Amazing, eh?