broken passphrase / reveal active passphrase on open LUKS [SOLVED]

[confrused]

My LUKS encrypted volume on an external drive is open and accessible in Linux Mint because I choose "Remember forever". However, it seems likely that *I* have not 'remembered forever' because I am unable to unlock it after I shutdown LM and then boot into Ubuntu. My question is, how can I find out what the passphrase is? It seems that should be possible since I have access to it in LM, I am hoping.

[Mute Ant]

LUKS itself uses the pass-phrase you enter, adds 'salt' and mashes it up thousands of times, to slow down automated guessing. That result applied to the 'wrapped-master-key' regenerates the 'unwrapped-master-key' needed to unscramble the data. None of that is supposed to be reversible and I am assuming it isn't... you can't use a 'cold' LUKS without an acceptable pass-phrase.

With a 'warm' LUKS, the master key is in RAM somewhere, but not the pass-phrase.

I would consider it a very dodgy implementation if the pass-phrase can be reverse-engineered from what's stored by 'Remember Forever', but I have never gone looking. It is your Mint desktop doing the remembering, so...
A: Which version of Mint are you using? 17, 17.1, 17.2 ... 18.3
B: Which desktop has remembered the pass-phrase? KDE, Cinnamon, MATE or XFCE?

[confrused]

LM 18.2 Cinnamon 64-bit
3.4.6
4.8.0-53-generic

[Mute Ant]

If you boot and log in to the Mint that has remembered the LUKS passphrase, then start the program seahorse it can show you the original passphrase.

[guess]The passphrase is remembered in the file ~/.local/share/keyrings/user.keystore encrypted using your login password.[/guess]

[confrused]

Seahorse did it. Thank you !

[Mute Ant]

Hurrah! If you edit the title of your original post to include Solved other readers will find it, and other members won't try to answer it.

[confrused]

Yes, I would like to do that! I can edit my title above for this reply, but how do I edit the original title?

[Mute Ant]

viewtopic.php?f=42&t=186483#p982667