[dm-crypt] LUKS header recovery attempt, bruteforce detection of AF-keyslot bit errors

protagonist listdump at depressiverobots.com
Sun Apr 30 17:06:57 CEST 2017

As a short update, I can confirm that when run with the default options,
pvcreate initializes the first 512 bytes of the LVM header block with
0x00, similarly to ext4, creating excellent known plaintext that is easy
to spot during debugging of decryption routines.

This is documented in the manpage of pvcreate:
"-Z, --zero {y|n}
Whether or not the first 4 sectors (2048 bytes) of the device should be
wiped. If this option is not given, the default is to wipe these sectors
unless either or both of the --restorefile or --uuid options were
specified."  https://linux.die.net/man/8/pvcreate

My current memcmp of the first 512 bytes therefore works just as well on
LVM as on ext4 and has managed to find a bit flip on a deliberately
corrupted key slot.

However, this is bad news for my ultimate target of recovering the
actual master key of the SSD in question, as it seems my previous
1-error checks have been unsuccessful, but valid.

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