[dm-crypt] cryptsetup FAQ section 6.10, master keys and cryptsetup-reencrypt (resend)

Arno Wagner arno at wagner.name
Mon Jan 9 06:39:43 CET 2017

Hi Michael,

yes, you are right. Thanks.

I think reencryption should be mentioned in Item 6.10. Fixed.


On Fri, Jan 06, 2017 at 13:53:37 CET, Michael Kjörling wrote:
> For some reason this e-mail has failed to show up on the list, so I'm
> sending it again. If this ends up being a duplicate, please accept my
> apologies in advance and feel free to delete this copy.
> I was poking around the cryptsetup FAQ, mostly out of idle curiosity,
> and noticed that section 6.10 (How do I recover the master key from a
> mapped LUKS container?) states that
> > Changing the master key requires a full data backup, luksFormat and
> > then restore of the backup.
> But as far as I understand it, this isn't the case any longer;
> https://gitlab.com/cryptsetup/cryptsetup/commits/master/src/cryptsetup_reencrypt.c
> says that cryptsetup-reencrypt was born in mid-2012, and my
> understanding is that changing the master key is one of the major use
> cases for cryptsetup-reencrypt (the other being to change from one
> cipher or set of cipher settings to another).
> Isn't it time that the FAQ is updated to at least point out the
> existence of cryptsetup-reencrypt?
> A backup would still very much be advised, but unless I'm mistaken,
> changing the master key is now merely an offline operation rather than
> a luks(re)Format operation.
> -- 
> Michael Kjörling • https://michael.kjorling.semichael at kjorling.se
>                  “People who think they know everything really annoy
>                  those of us who know we don’t.” (Bjarne Stroustrup)
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Arno Wagner,     Dr. sc. techn., Dipl. Inform.,    Email: arno at wagner.name
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