[dm-crypt] Using a removable-device-recorded passphrase to decrypt a system

Arno Wagner arno at wagner.name
Fri Jun 26 14:30:47 CEST 2015

Hi Arbiel,

I think you have some misunderstanding here: crypttab does 
not work for encrypted system, as it is on that encrypted system 
itself (catch-22). 

In order to have an encrypted system partition, you need some 
mechanism in the initrd to read your passphrase. What form that 
mechanism takes depends on the distribution you are using.

My advice is to not encrypt the system partition itself, just
all user and data partitions. An "evil Maid" attacker can get
into your boot process anyways. Disk encryption really only 
protects against encrypted devices being stolen while not 
mapped (machine is off, e.g.).


On Thu, Jun 25, 2015 at 16:57:33 CEST, Arbiel (gmx) wrote:
> Hi
> I decided to use a 512-byte randomly generated passphrase to crypt my
> system partition. I recorded this passphrase on a removable device (USB
> key) and correctly wrote the crypttab and fstab files and updated my
> initrd.img for all this to work.
> I am anxious now to replicate my passphrase on additionnal USB keys, in
> case my primary USB key get lost or damaged.
> For some reasons, I cannot name all partitions where my passphrase will
> be recorded with a unique label.
> I tried to write several lines in the crypttab file for defining as many
> passphrase locations as necessary such as
> root UUID=uuid /dev/disk/by-label/USBkey1/passphrase:x
> luks,keyscript=/lib/cryptsetup/scripts/passdev
> root UUID=uuid /dev/disk/by-label/USBkey2/passphrase:x
> luks,keyscript=/lib/cryptsetup/scripts/passdev
> and so on, but this does not work.
> I thank in advance anybody who can advise me on how to solve this issue.
> Arbiel

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Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
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