Re: [gentoo-user] Re: Securely deletion of an HDD

Re: [gentoo-user] Re: Securely deletion of an HDD

[wireless]

On 07/13/2015 10:10 AM, Grant Edwards wrote:

>> With regards to the other replies: I think physical destruction is
>> unnecessary, and I don't really want to go through the trouble.
> If it's "trouble" rather than "fun", then you're doing it wrong. :)

Brilliant statement::

> Others favor a high-powered rifle or an 8lb sledge.


In my impetuous youth, The first time I got to work under an old
AT&T unix license, we had several heated debates with nerds from DC
and Jersey..... turns out I was right; you could kill an "phone switch"
with a single shot (and old at&t 3Bx series).

I took out a .338 with a questionable round and one shot turned off
3 out of 4 drives and most of the processors. The a_holes went back
to their  agency; and I lost some very valuable potential clients.
But Grant is most correct!; if it ain't fun why fork with it?

I did become great friends with some folks from the jersey labs......

cheers!
James

[gentoo-user] Re: Securely deletion of an HDD

[Grant Edwards]

On 2015-07-15, wireless@tampabay.rr.com <wireless@tampabay.rr.com> wrote:

> In my impetuous youth, The first time I got to work under an old
> AT&T unix license, we had several heated debates with nerds from DC
> and Jersey..... turns out I was right; you could kill an "phone switch"
> with a single shot (and old at&t 3Bx series).

Back in the 80s I worked for a company that made/sold radio-telephony
mobile and base station equipment (which is basically a PBX connected
to a bank of radio transceivers instead of phone sets).  They had more
than a few systems installed in various Central and South American
countries during the 60s and 70s (the worse the standard copper
infrastructure, the more important mobile phones tended to be).

The field service guys told me that a not uncommon failure mode for
the base station equipment was bullet holes.

It turns out that one of the first things you do during a coup in a
small central/south american county is take over or disable the
radio-telphone base stations.  [Back then the base stations were much
higher power and covered much larger areas than a cellular base
station does these days.]

-- 
Grant Edwards               grant.b.edwards        Yow! Is something VIOLENT
                                  at               going to happen to a
                              gmail.com            GARBAGE CAN?

[gentoo-user] Re: Securely deletion of an HDD

[James]

Grant Edwards <grant.b.edwards <at> gmail.com> writes:


> It turns out that one of the first things you do during a coup in a
> small central/south american county is take over or disable the
> radio-telphone base stations.  [Back then the base stations were much
> higher power and covered much larger areas than a cellular base
> station does these days.]


Yep:: Then when I got my first research lab, guess what was our first
'Big Donation' ?   A semi trailer full of every make of those old at&t
unix systems; from 3B2's own up the ladder to working switchgear.
We wiped them clean and put Mt. Xinu unix (BSD) on them just to tick
off the at&t folks....  Funny thing was they just kept giving us more and
more equipment...


Kids now a days do not get to play with the 'toys' we did in college.
At poker flats [1] we got to shoot off rockets into the ionosphere. Try
that one today.... The father of the modern rocket [2] taught my son
Multi-Variable Calculus.... Small world when you get down to it....

Want to see the latest in Mach 7 guns?




cheers!
James

[1] http://www.pfrr.alaska.edu/

[2]
http://motherboard.vice.com/blog/lebanons-forgotten-space-race-in-1961-manoug-manougian-aimed-the-middle-east-at-the-stars

[gentoo-user] Securely deletion of an HDD

[Marc Joliet]

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Hi,

I have to failed drives that I want to give away for recycling purposes, but
want to be sure to properly clear them first.  They used be part of a btrfs
RAID10 array, but needed to be replaced (with "btrfs replace").  (In the
meantime I converted the array to RAID1 with only two drives.)

My question is how precisely the disks should be cleared.  From various sources
I know that overwriting them with random data a few times is enough to render
old versions of data unreadable.  I'm guessing 3 times ought to be enough, but
maybe even that small amount is overly paranoid these days?

As to the actual command, I would suspect something like "dd if=/dev/urandom
of=/dev/sdx bs=4096" should suffice, and according to
https://wiki.archlinux.org/index.php/Random_number_generation#.2Fdev.2Furandom,
/dev/urandom ought to be random enough for this task.  Or are cat/cp that much
faster?

Any thoughts?

Greetings
-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup

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Re: [gentoo-user] Securely deletion of an HDD

[Rich Freeman]

On Sun, Jul 12, 2015 at 8:35 AM, Marc Joliet <marcec@gmx.de> wrote:
>
> My question is how precisely the disks should be cleared.  From various sources
> I know that overwriting them with random data a few times is enough to render
> old versions of data unreadable.  I'm guessing 3 times ought to be enough, but
> maybe even that small amount is overly paranoid these days?
>
> As to the actual command, I would suspect something like "dd if=/dev/urandom
> of=/dev/sdx bs=4096" should suffice, and according to
> https://wiki.archlinux.org/index.php/Random_number_generation#.2Fdev.2Furandom,
> /dev/urandom ought to be random enough for this task.  Or are cat/cp that much
> faster?

I'd probably just use a tool like shred/wipe, but you have the general idea.

I'd probably follow it up with an ATA secure erase - for an SSD it is
probably the only way to be sure (well, to the extent that you trust
the firmware authors).

If it weren't painful to set up and complicated for rescue attempts,
I'd just use full-disk encryption with a strong key on a flash drive
or similar.  Then the disk is as good as wiped if separated from the
key already.

-- 
Rich

Re: [gentoo-user] Securely deletion of an HDD

[Marc Joliet]

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(Thanks to everyone for the replies so far!)

Am Sun, 12 Jul 2015 08:48:48 -0400
schrieb Rich Freeman <rich0@gentoo.org>:

> On Sun, Jul 12, 2015 at 8:35 AM, Marc Joliet <marcec@gmx.de> wrote:
> >
> > My question is how precisely the disks should be cleared.  From various sources
> > I know that overwriting them with random data a few times is enough to render
> > old versions of data unreadable.  I'm guessing 3 times ought to be enough, but
> > maybe even that small amount is overly paranoid these days?
> >
> > As to the actual command, I would suspect something like "dd if=/dev/urandom
> > of=/dev/sdx bs=4096" should suffice, and according to
> > https://wiki.archlinux.org/index.php/Random_number_generation#.2Fdev.2Furandom,
> > /dev/urandom ought to be random enough for this task.  Or are cat/cp that much
> > faster?
> 
> I'd probably just use a tool like shred/wipe, but you have the general idea.

Ah, I overlooked that shred can operate on device files!  Thanks.  I especially
trust shred, since my main source was an article by its author
(https://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html).

With regards to the other replies: I think physical destruction is unnecessary,
and I don't really want to go through the trouble.  The key bit in the above
article is:

"[...]. If these drives require sophisticated signal processing just to read
the most recently written data, reading overwritten layers is also
correspondingly more difficult. A good scrubbing with random data will do about
as well as can be expected."

And this was in 1996!  Drives have only gotten denser since then (e.g.,
perpendicular recording), and the epilogues (which reiterate the above) suggest
that nothing has changed to make old data more recoverable.  I noticed that the
info manual to shred even says:

"On modern disks, a single pass should be adequate, and it will take one third
the time of the default three-pass approach."

The Arch wiki also arrives at the same conclusion (see
https://wiki.archlinux.org/index.php/Securely_wipe_disk#Residual_magnetism),
and provides some additional references.

> I'd probably follow it up with an ATA secure erase - for an SSD it is
> probably the only way to be sure (well, to the extent that you trust
> the firmware authors).

Yeah, that sounds like a good idea.  In the case of HDDs, even if I can't trust
the firmware, I've already wiped what I can.  With regards to SSDs, I've been
meaning to read http://www.cypherpunks.to/~peter/usenix01.pdf.

So my intermediate summary is:  I'll probably use shred with one pass, followed
by ATA (Enhanced) Secure Erase to erase the reallocated sectors (though I'll
have to fiddle with my BIOS to do that). I'll be sure to read
https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase first.

> If it weren't painful to set up and complicated for rescue attempts,
> I'd just use full-disk encryption with a strong key on a flash drive
> or similar.  Then the disk is as good as wiped if separated from the
> key already.

Plus you don't have to worry about reallocated sectors (which might only
contain single bit errors). Currently I'm planning on waiting for btrfs to
support it. Chris Mason recently mentioned that it's definitely something they
want to look at (https://youtu.be/W3QRWUfBua8?t=631), and it's not something
that is so important to me personally that I have to have it right this instant.

-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup

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[gentoo-user] Re: Securely deletion of an HDD

[Grant Edwards]

On 2015-07-12, Marc Joliet <marcec@gmx.de> wrote:

> With regards to the other replies: I think physical destruction is
> unnecessary, and I don't really want to go through the trouble.

If it's "trouble" rather than "fun", then you're doing it wrong. :)

There's thermite:

  http://hackaday.com/2008/09/16/how-to-thermite-based-hard-drive-anti-forensic-destruction/

And mechanical shredding:

  http://www.youtube.com/watch?v=AZdZGKyu9hc

Others favor a high-powered rifle or an 8lb sledge.

-- 
Grant Edwards               grant.b.edwards        Yow! Sometime in 1993
                                  at               NANCY SINATRA will lead a
                              gmail.com            BLOODLESS COUP on GUAM!!

Re: [gentoo-user] Re: Securely deletion of an HDD

[Marc Joliet]

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Am Mon, 13 Jul 2015 15:03:10 +0000 (UTC)
schrieb Grant Edwards <grant.b.edwards@gmail.com>:

> On 2015-07-12, Marc Joliet <marcec@gmx.de> wrote:
> 
> > With regards to the other replies: I think physical destruction is
> > unnecessary, and I don't really want to go through the trouble.
> 
> If it's "trouble" rather than "fun", then you're doing it wrong. :)

OK, you have a point ;-) .

> There's thermite:
> 
>   http://hackaday.com/2008/09/16/how-to-thermite-based-hard-drive-anti-forensic-destruction/
> 
> And mechanical shredding:
> 
>   http://www.youtube.com/watch?v=AZdZGKyu9hc
> 
> Others favor a high-powered rifle or an 8lb sledge.

That does look fun!  However, I meant along the lines of destroying the disk
surface, because I want to give the HDDs away for recycling (a computer chain I
occasionally buy from collects old hardware for this purpose).  Good for the
environment and all that :-) .

-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup

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