Resetting your Master Password on 10.4.
I recently ran into a situation where the master password for a Mac had been set, but nobody could remember what it was. Since there wasn’t any FileVault-enabled accounts on the Mac, this wasn’t a killer problem yet, but it could be at some point so we wanted to get it fixed. Here’s how you do it on 10.4 (should also work on 10.3, but we didn’t test that.)
Go to /Library/Keychains/
Delete the two Filevault files by throwing them in the trash. (Authenticate as an admin account when prompted.)
Go to System Preferences: Security and reset the master password to the correct one there.
(Hat tip: Random Techie Mac Stuff)