[dm-crypt] Mechanics

julie_nuckey at trendmicro.co.uk julie_nuckey at trendmicro.co.uk
Wed Dec 2 12:20:31 CET 2009

I'm trying to understand the mechanics of how dm-crypt and cryptsetup work, in particular how data such as the password/key-file data is passed from user mode to kernel mode, and also generally what does what when setting up an encrypted volume.


As I understand it, dm-crypt is a pure kernel-mode application that does the encryption and decryption of data on the fly. It works independently of any on-disk format such as metadata like that used by LUKS. Have I got that right?


And cryptsetup is the pure user-mode application and this can work in "plain" mode, ie without LUKS, or in LUKS mode. Is that right? So how does the password/key get from cryptsetup (user mode) to dm-crypt (kernel mode) and does it differ depending on whether I'm using plain or LUKS mode? Does it use tables? Is the password/key written to the tables?


In LUKS mode, does cryptsetup generate the master key? In user mode? Does cryptsetup create/edit the metadata?


Thanks in advance for any clarification anyone can provide.


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