[dm-crypt] nuke password to delete luks header

Thomas Bastiani thom at codehawks.eu
Thu Jan 16 11:30:28 CET 2014

Hi guys,

I've been following this discussion for a few days. And I feel like giving
my opinion... :-)

On 16 January 2014 09:50, Ondrej Kozina <okozina at redhat.com> wrote:

> On 01/15/2014 09:27 PM, Milan Broz wrote:
>> On 01/14/2014 05:30 AM, Arno Wagner wrote:
>>> I think that in your scenario, "nuke" does not have any real
>>> advantages over just not having the passphrase, and that one
>>> is dangerous.
>> Well, this idea is not new and I responded very similar months ago.
>> http://code.google.com/p/cryptsetup/issues/detail?id=110#c1
>> But seems there is a lot of people in disagreement.
>> I was quite surprised that most of people from
>> our university security&crypto lab I met today and asked
>> (to have some other opinions) said that despite "nuke password"
>> has very limited use it is worth to have something like that...
>> Sigh... :)
> In that case, let me join you with my humble Sigh as well.

Yes, I also tend to agree with Arno's arguments and I feel that there is no
real (non-dangerous) use case for this.

>  But what I really want to avoid is that every distribution will
>> add some random patches implementing something like this.
>> It is perhaps better to implement and document this upstream.
I would argue that it's really independent from any actual crypto logic.
The only thing that need's to be done is wrap the password/key prompt and
check the password against a known salted hash or PBKDF (same as all Linux
distros do). Then "nuking" the container is actually quite simple. Just
erase the LUKS header by zeroing it. This is not any more complex than what
distros already have to do to support root-on-LUKS.

Actually this functionality is simple enough that anyone actually wanting
it can just write their own password prompt wrapper script.

I would point out that this doesn't require any more information from LUKS
internals than mouting a block device from /etc/crypttab would. And so it's
entirely possible to keep the code layered and simple. KISS applies.

Moreover, I think it's wrong to assume that distros don't share any of
their code. Proof is, they fork each other. It wouldn't have to be
implemented a dozen times.

> Ok, I just think that this new feature is quite heavily disputed already.
> This is perhaps third discussion I found on that topic in a few minutes of
> searching. Please, make "nuke password" option configurable so that it can
> be easily removed from any distribution that wouldn't agree with arguments
> for including it.
> Best regards
> Ondra
> _______________________________________________
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> dm-crypt at saout.de
> http://www.saout.de/mailman/listinfo/dm-crypt

Just my .02$,
Thomas Bastiani
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