PSA for LUKS users

PSA for LUKS users

[Felix Lechner via]

Hi,

Given the broad popularity of LUKS full-disk encryption among our
fellow Guix users, I thought the community might appreciate reading
about potentially weak key-derivation functions in older LUKS
installations. [1]

The article even offers fixes, although I cannot say whether your
system will boot after you follow the steps since I do not use LUKS
personally. Stay safe!

Kind regards
Felix Lechner

[1] https://mjg59.dreamwidth.org/66429.html

Re: PSA for LUKS users

[Vagrant Cascadian]

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On 2023-04-19, Felix Lechner via wrote:
> Given the broad popularity of LUKS full-disk encryption among our
> fellow Guix users, I thought the community might appreciate reading
> about potentially weak key-derivation functions in older LUKS
> installations. [1]
>
> The article even offers fixes, although I cannot say whether your
> system will boot after you follow the steps since I do not use LUKS
> personally. Stay safe!
...
> [1] https://mjg59.dreamwidth.org/66429.html

In short, those instructions will almost certainly break Guix System!

While recent grub2 finally has limited support for luks2, it only
supports the weaker KDF (key derivation function) (PBKDF2?), as I
understand it, though would be happy to be proven wrong!

Because Guix System does not yet support a separate /boot partition,
this means if you want "full-disk encryption" you are limited to weak
KDF for the whole filesystem, instead of just a weak /boot partition
(e.g. either luks1, luks2 with weaker pbkdf2, or entirely
unencrypted). There is a bug about being able to use a split /boot
partition:

  https://issues.guix.gnu.org/48172

Alternately, you could probably get a weaker encrypted rootfs (using
luks1 or luks2+PBKDF) and still have a state-of-the-art luks2+argon2id
partition for /home. Maybe if you were adventurous /var/guix, which
might allow detecting a compromise with "guix gc" which contains the
checksums of files in /gnu/store?

With both the split /boot approach or the weaker rootfs with stronger
/home partition, there is some risk of a (admittedly very sophisticated
and still probably quite expensive) evil maid attack.

  https://en.wikipedia.org/wiki/Evil_maid_attack


Well... fun times, folks!


live well,
  vagrant

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Re: PSA for LUKS users

[Jonathan Brielmaier]

Am 20.04.23 um 06:03 schrieb Vagrant Cascadian:
> On 2023-04-19, Felix Lechner via wrote:
>> Given the broad popularity of LUKS full-disk encryption among our
>> fellow Guix users, I thought the community might appreciate reading
>> about potentially weak key-derivation functions in older LUKS
>> installations. [1]
>>
>> The article even offers fixes, although I cannot say whether your
>> system will boot after you follow the steps since I do not use LUKS
>> personally. Stay safe!
> ...
>> [1] https://mjg59.dreamwidth.org/66429.html
>
> In short, those instructions will almost certainly break Guix System!

Can confirm :) At least the described backup & restore procedure does work.

I also think, that our cryptsetup is quite old, so I built a patch for
updating: https://issues.guix.gnu.org/62960

> While recent grub2 finally has limited support for luks2, it only
> supports the weaker KDF (key derivation function) (PBKDF2?), as I
> understand it, though would be happy to be proven wrong!

The support seems pretty limited, as I only updated the LUKS version of
my root-partition to version 2 (still PBKDF) and it already refused to
boot...

~Jonathan

Re: PSA for LUKS users

[Attila Lendvai]

> While recent grub2 finally has limited support for luks2, it only
> supports the weaker KDF (key derivation function) (PBKDF2?), as I
> understand it, though would be happy to be proven wrong!


i have just spent half an hour reading the linked PR's and patch emails, and unfortunately you seem to be right.

i don't see why progress is so slow on this. some of the patches are 5+ years old! and the submitters seem to be constructive and responsive.

a good entry point that collects the relevant links:

https://github.com/johnlane/grub/issues/21

-- 
• attila lendvai
• PGP: 963F 5D5F 45C7 DFCD 0A39
--
“The probability of the people in power being individuals who would dislike the possession and exercise of power is on a level with the probability that an extremely tender-hearted person would get the job of whipping-master on a slave plantation.”
	— Frank H. Knight

Re: PSA for LUKS users

[kiasoc5]

On 4/20/23 05:39, Attila Lendvai wrote:
>> While recent grub2 finally has limited support for luks2, it only
>> supports the weaker KDF (key derivation function) (PBKDF2?), as I
>> understand it, though would be happy to be proven wrong!
> 
> 
> i have just spent half an hour reading the linked PR's and patch emails, and unfortunately you seem to be right.
> 
> i don't see why progress is so slow on this. some of the patches are 5+ years old! and the submitters seem to be constructive and responsive.
> 
> a good entry point that collects the relevant links:
> 
> https://github.com/johnlane/grub/issues/21
> 

Argon2 support was slated to be in the next release of Grub (2.12) but 
apparently this is not realistic:

https://www.mail-archive.com/grub-devel@gnu.org/msg35370.html

Re: PSA for LUKS users

[Josselin Poiret]

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It would probably be doable to run a very small Linux EFI stub as a
bootloader on x86, that way you can side-step the lacking grub support.
Integrating it with Guix would surely be a bit harder though.

kiasoc5 <kiasoc5@disroot.org> writes:

> Argon2 support was slated to be in the next release of Grub (2.12) but 
> apparently this is not realistic:

As for LUKS2 support in Grub, as long as you use PBKDF2 it should now be
supported by HEAD.

Best,
-- 
Josselin Poiret

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