gbde blackening feature - how can on disk keys be "destroyed" thoroughly?

[Poul-Henning Kamp]

In message <200507142037.j6EKbaf12941 at parrot.ebi.ac.uk>, David Kreil writes:
>
>Dear Poul-Henning,
>
>After a job induced pause in my strong interest in encryption solutions, 
>I have on my return tried to learn what has since changed with gbde. I must
> be missing the obvious because I cannot locate a "changelog" or "release
> notes" document.

Not much has happened :-)

In FreeBSD you need to study the cvs logs to see what happened.

http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/geom/bde/?hideattic=0

>You have been most helpful in our discussion last year. I have now, in 
>particular, been wondering whether you have since at all had a chance of 
>revisiting the issue of blackening keys with multiple physical random 
>overwrite before resetting them to zero to avoid key recovery by methods 
>as available from companies like www.dataclinic.co.uk.

I have talked with some people from various disk manufactureres who
know what they talk about and their unanimous advice is: "forget it".

The geometry of modern disk R/W heads does not allow you to do anything
which will be really efficient.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.