[Pkg-cryptsetup-devel] Bug#371135: encrypted swap with variable key fails

[Andrew Pimlott]

As a non-expect in cryptsetup who just wants his swap space back, let me
see if I understand the problem.

Automatically formatting a swap partition is a destructive operation, so
all reasonable checks should be made before doing it.  It is currently
not possible to positively identify a swap partition encrypted with a
random key; nor is it possible to negatively identify a partition as not
encrypted (with some unknown key).  This gives me two ideas:

1.  Create a marking for partitions to be encrypted with a random key,
    allowing for the positive identification above.  Perhaps this should
    be part of LUKS.

2.  If I use LUKS for all encrypted filesystems, I believe it is
    possible to perform the negative identification above.  That is, if
    I don't see the LUKS header, and the partition does not have an
    unencrypted volume, then it is safe to destroy.  So let me promise
    that I have no non-LUKS encrypted filesystems.

It would be a shame to require extra configuration for encrypted swap
with a random key, as this is a commonly recommended setup.
Furthermore, it not "fundamentally dangerous"; the only reason it is
dangerous today is that we don't mark partitions clearly enough, and
that could change.  So we should be able to find a solution.

On the other hand, I'm glad you guys are so concerned with the safety of
my data!

Andrew