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Keyfile Support for GRUBs LUKS

From: Ralf Ramsauer
Subject: Keyfile Support for GRUBs LUKS
Date: Wed, 20 Nov 2013 00:43:37 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0


yesterday I realised, that GRUB is already supporting LUKS and even
simple DSA signature checking.

I was thinking about the following setup:
  - fully encrypted harddisk (LUKS) (incl. rootfs).
  - no bootloader on harddisk
  - kernel + initrd inside encrypted partition
  - optionally: signatures of the kernel + initrd

For "trusted" booting, I thought about an USB stick, that just includes
GRUB, a public key for verification and a keyfile for LUKS.
Using that setup, no password input would be required during boot. The
USB stick can be considered as "trusted environment".

Unfortunately, GRUB doesn't support keyfile for Luks up to now. As I'm
quite familiar with dm-crypt and LUKS I tried to implement the keyfile
feature to GRUB.
After spending several hours trying to get a deeper insight into the
GRUB internas I finally resigned, as I was missing documentation on
several things...

I was very confused about the way how GRUB2 is handling its modules and
about the strategies how functions are exactly called.
The aim is to implement three additional options to cryptodisk.c resp.
 -k keyfile [e.g. (hd2,msdos3)/mysecretkey]
 -o keyfile offset [optional, default: 0]
 -s keyfile size [optional, default: keyfilesize]

Using LUKS, a keyfile can simply be treated like a passphrase, which
basically is already implemented.

I would appreciate, if perhaps someone of you could help me with this issue.

Thanks in advance!

Ralf Ramsauer

PGP: 0x8F10049B

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