From: Arno Wagner <arno@wagner.name>
To: dm-crypt@saout.de
Subject: Re: [dm-crypt] Securely erase LUKS header
Date: Sun, 10 Mar 2013 20:23:12 +0100 [thread overview]
Message-ID: <20130310192312.GA9676@tansi.org> (raw)
In-Reply-To: <40727.130.226.154.66.1362921572.squirrel@lavabit.com>
On Sun, Mar 10, 2013 at 09:19:32AM -0400, hephey@lavabit.com wrote:
> I'm having trouble calculating the amount of data I need to erase in the
> header.
>
> The af-stripes appears to be hardcoded to 4000, according to the
> specification [1].
>
> First I made an encrypted loop-device, using default options:
>
> cryptsetup luksFormat /dev/loop0
>
> I then made a header backup, using
>
> cryptsetup luksHeaderBackup --header-backup-file /tmp/header.img /dev/loop0
>
> The size of this backup (/tmp/header.img) is exactly 1.052.672 bytes,
> which fits with the number given in the FAQ (see 5.4) [2]. I'm asumming
> that cryptsetup's calculation is correct.
>
> In the FAQ it's also stated that to wipe the header, I need to use to
> formula:
>
> header size = (keyslots x stripes x keysize) + offset bytes
In 5.4, I state just to wipe the first 10MB to be safe.
Do I have the formula above anywthere as explicitely
recommended for wipes? Is so, plese tell me where, so I
can fix it.
Arno
--
Arno Wagner, Dr. sc. techn., Dipl. Inform., Email: arno@wagner.name
GnuPG: ID: CB5D9718 FP: 12D6 C03B 1B30 33BB 13CF B774 E35C 5FA1 CB5D 9718
----
One of the painful things about our time is that those who feel certainty
are stupid, and those with any imagination and understanding are filled
with doubt and indecision. -- Bertrand Russell
next prev parent reply other threads:[~2013-03-10 19:23 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-10 13:19 [dm-crypt] Securely erase LUKS header hephey
2013-03-10 14:48 ` Milan Broz
2013-03-10 19:23 ` Arno Wagner [this message]
2013-03-13 21:45 ` [dm-crypt] hardware encryption lxnf98mm
2013-03-13 22:01 ` .. ink ..
2013-03-14 11:12 ` lxnf98mm
2013-03-14 12:16 ` Michael Stapelberg
2013-03-15 13:22 ` lxnf98mm
2013-03-14 13:14 ` Matthias Schniedermeyer
2013-03-14 20:50 ` Yves-Alexis Perez
2013-03-14 20:59 ` Yves-Alexis Perez
2013-03-15 16:18 ` Matthias Schniedermeyer
2013-03-14 16:20 ` Thomas Bächler
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