Comment 2 for bug 1439869

Crypsetup returns 0 on success or non-zero on error.

       Error codes are: 1 wrong parameters, 2 no permission (bad passphrase),
       3 out of memory, 4 wrong device specified, 5 device already exists or
       device is busy.

http://manpages.ubuntu.com/manpages/precise/man8/cryptsetup.8.html