LUKS multiple key slots - what's the intuition? LUKS volumes have the ability to allow multiple independently usable passwords, as explained here:
[https://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions]    

The intuition behind basic encryption with a single key is pretty straightforward.

ciphertext = BIG_FUNCTION(plaintext, key)
plaintext = BIG_FUNCTION^(-1)(ciphertext, key)


Can anyone explain how a LUKS volume can permit independently usable passwords? I'm just looking for the intuition - not necessarily a detailed explanation of how LUKS in particular handles this.
Roughly your password is used to encrypt a MasterSecretKey. Then you use this MasterSecretKey with a symmetric algorithm to encrypt or decrypt your data (the disk sectors).
They eight key slots in LUKS are eight different encryptions of the same MasterSecretKey under eight different passwords.

See also this image:  (original web page: http://auto0.info/secret-messages-download-red-hat-fedora)
(original image http://nnc3.com/LM10/Magazine/Archive/2005/61/065-071_encrypt/images/fig3-partition-header.png is not more available)

Actually LUKS does not encrypt the MasterSecretKey with a password but with a key, generated with a PBKDF.

A similar approach is used by GPG when you send a message to a set of distinct recipients.

This is usally know as KEM/DEM paradigm: Key Encapsulation Method/Data Encapsulation Method and it is the standard method when you use public key to encrypt something.