Apple’s support document for FileVault 2 (a.k.a. “full disk encryption” or “FDE”) has lots of information about enabling FDE and what it means for booting the machine. However, it doesn’t cover one very important thing I’m trying to do: mount the drive in the Recovery HD environment to reinstall OS X on it. The Recovery HD environment asks me for the volume passphrase so it can mount my drive and try to install OS X onto it. If this were an external drive which I’d manually enabled FDE on with diskutil, or an external Time Machine volume, I’d know it because it makes you pick one (just like a regular login password), but FileVault 2 never asked me for a volume passphrase (I assume it selects one behind the scenes). I’ve tried my main user’s password, but that doesn’t work, and neither does the recovery key set for the volume. Keychain Access doesn’t have anything that I could find. How do I unlock this volume?