Date: Sun, 05 Sep 2004 15:26:42 +0100 From: David Kreil <kreil@ebi.ac.uk> To: "Poul-Henning Kamp" <phk@phk.freebsd.dk> Cc: freebsd-questions@freebsd.org Subject: Re: gbde blackening feature - how can on disk keys be "destroyed" thoroughly? Message-ID: <200409051426.i85EQgB18118@puffin.ebi.ac.uk> In-Reply-To: Your message of "Sun, 05 Sep 2004 14:13:52 %2B0200." <25405.1094386432@critter.freebsd.dk>
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Dear Poul-Henning,
> >> On a modern disk there is no sequence of writes that will guarantee
> >> you that your data is iretriveable lost.
> >> Even if you rewrite a thousand times, you cannot guard yourself against
> >> the sector being replaced by a bad block spare after the first write.
> >
> >Good point. In the rare chance event that this happens, it would indeed be
> >bad
> >news as an attacker would then only have to scan the bad blocks for possible
> >copies of the key.
>
> He still has no way of recognizing the key though...
Right, he'd have to try them all.
> >A simple improvement on the present situation would already be if
> >the keys were not overwritten with zeros but with random bits. I
> >don't know how difficult it would be to attempt to physically write
> >random bits multiple times but it would much strengthen the feature
> >apart from the rare cases when the sectors of the masterkey have
> >been remapped into bad blocks.
>
> Please read the paper, there is a reason why it is zero bits.
Sorry, forgot.
> >What do you think? Is the required effort disproportional to the
> >intended value of the blackening feature?
>
> Blackening adds no significant incremental security imo,
>From a security point of vie, yes. From a social/civil-liberties/legal point
of view, I felt it was an excellent thing to have.
> on the
> other hand it is feasible to implement it, so I've put it on the
> todo list.
That's great, thanks a lot!
With best regards,
David.
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University of Cambridge (_Y_.)' ._ ) `._ `. ``-..-'
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