I recently encrypted a disk with luks v 1.1.3. I can lock and unlock it without problems. So now I want to change to a new passphrase.
I'm using the "Disk Utility" on Debian 7.7. So I type int the current passphrase, two copies of the new passphrase, click authenticate, and type my root password.
It then complains my current passphrase is incorrect. Start over.
X10 times, no joy.
So I unlock the disk with the current passphrase and it opens fine. So I repeat the above, no joy.
X10 times.
But the current (soon to be old) passphrase unlocks the device no prob.
WHAT IS GOING ON HERE???

Every luks has a master password and user password. It might be asking for master password.

You can always change the key in terminal if disk utility isn't working out.

and of course, make sure you don't forget the new pass. You can also just add the new key and keep the old one until you're sure the new one is good.