Cryptsetup question

[Leon Smith]

I'm having some difficulty making a LUKS container which *requires*
multiple keys/passphrases to open rather than allows one of multiple
keys to be used in order to open it.

The documentation manual unfortunately doesn't seem to cover doing
anything near what I have in mind.

For a comparison and explanation of where I got the idea, I have a few
truecrypt containers which do exactly what I have in mind, opening only
if their passphrase *and* keyfiles are given. Naturally, given the way
truecrypt has gone, I am trying to discontinue its use.

How would I go about replicating a similar scheme?

- L.S.