Wiping a hard drive?

[Arno Wagner]

Errr, reinforces it?

Sorry. Misunderstood that. Ok then ;-)

Obviously you know about it. Anyone with more than a passing
acquaintance with electronics can see the difficulty of defending
comprehensively against a non-trivial investigator using TEMPEST-like
techniques. (The optical-TEMPEST attack I referred to used nothing more
sophisticated than a fast-acting photodiode and a high-speed data
capture device, plus some software.)

That was a pretty impressive attack. I read the paper. I would have
thought before that the phosphorpus in the CRT would filter enough
due to its slowness. Obviously not! And this can be done way cheaper
and from farther away than traditional EM TEMPEST.

High-tech investigation however will not reveal what is written
in pencil on a piece of paper that they don't have sight of at a range
of less than a few hundreds of metres.

Another example: There are techniques to deduce from sound
what was typed on a keyboard. (Pretty new.) No such techniques
for handwriting (yes), as the problem is far more difficult, and
may be unsolvable (not enough sound, vanishes in the noise,
bad repeatability).

A secret message that is not
written down, but is contained in a person's memory, cannot be
intercepted without the courier person being aware of it, which means
that you're totally dependant on old-fashioned, "HUMINT" techniques of
infiltration, subversion and/ or theft. All of these are vastly more
expensive per bit of recovered data than, say, SIGINT (signals
intelligence), so less data can be recovered.

And some countries are unwilling to risk people in the field for
some strange reasons. Pretty crippling. Especially when an important
pice of SIGINT needs to be confirmed, such as, say, the location
of some WMDs....

Going back to the previous topic: yes, if PGP etc were proved to
be systematically breakable, then computer-savvy criminals and
surveillence-phobic people will simply stop entrusting their secret
data to PGP-encrypted channels, and will probably stop using emails at
all. If they're using emails at the moment.

Exactly. As soon as it is known to be compromised, the channel will
be abandoned and surveilance of it will become ineffective.

Arno

 

[Arno Wagner]

Spamhaus?
Sure they could move to a different domain name, but the Indiana
court could block service to the SpamHaus organisation as such. so you'd
end up in a cat-n-mouse game, until Spamhaus ended up with nowhere to
go.

The way I understand it, the problem is that Spamhaus is located within
the jurisdiction of this particular court, or that at least their
domain name is.

On the other hand, if a .org domain root was established which
cared not a hoot about the rulings of some North American parochial
court, then Spamhaus.org could remain in the myriads of configuration
files that use it, and DNS queries that couldn't resolve Spamhaus.org
would need to be re-configured to check this alternative .org root
service. Which is something that's being discussed with respect to the
rest of the Internet (well, DNS at least), in the event that the present
root servers be brought down for some reason. Some countries don't want
this to happen ; other countries see it as being highly desirable to not
be reliant on a single country for that sort of globally critical
service. It's the same logic that's leading the EU and Russia to be
putting up GPS-compatible satellites of their own.

Redundancy does not only help against technical failure. Done right
it can also help against political or administrative failure or
attacks.

<GRIN> Excuse me - I must go and register
"SpamHausLuvsIndiana.org", right now.

Nice! Good luck!

I'll let a Chinese person take you up on that <G>.

See my other posting. Seems you are rtight.

Arno

 

[Arno Wagner]

Maybe I'm misinterpreting what you're saying. I mean if we're trying
to recover data from some disk that's been overwritten or is making a
weak signal for some reason, we can possibly get a stronger signal by
reading much slower. I don't mean making the bits smaller, I mean
trying to read existing (but overwritten) bits. Another way to
increase the S/N ratio in a lab situation might be to chill the disk
and the read probe, maybe even with liquid helium or something.

I agree to what you say. But my impression is that it is not a S/N
issue at all, the data on the disks is all the surface can take.
Residual older bits are erased completely by the new data.

Right, this may put an upper limit on how much data recovery effort
is worthwhile.

Sounds reasonable. I can imagine data structures where recovery of
any sector causes a real security failure, but it gets a bit contrived.

http://www.actionfront.com/ts_whitepaper.aspx
(saved from here a few months back, thanks)

Ah, yes. I believe that was the one. Thanks!

Yeah, it's an interesting topic, we had a big discussion about it on
sci.crypt a few months ago:

http://groups.google.com/group/sci.crypt/browse_frm/thread/d1c1ce279ad0ab4b/3fedf36049799af6

Google-groups is great! I have an occasional look into sci.crypt,
but stopped reading it regularly a long time ago. Too low
S/N ratio...

There wasn't a definite conclusion, but valid points were brought up
on both sides. The stuff I've mentioned here comes partly from that
thread. Of course on sci.crypt we're trying to defend against
realistically impractical attacks all the time (planetary-scale
parallel computers and so forth), something like proving things in
math vs. just being sure of them in practice.

Of course. And it is an ongoing topic. For magnetic media that
do not reach the surface limits, this _is_ still a very valid
problem. And it may come up again if new materials are
discovered.

Hmm, interesting. Such products do get broken all the time, usually
due to silly design and implementation errors.

Indeed.

Arno

 

[Arno Wagner]

Cast your mind back ... 2 years ? ... to the spying/ data
mis-handling scandals at Los Alamos.
Some of the comments made in public about those cases implied
that the actual crimes committed were pilfering discs from stocks
audited for *physical destruction* , and taking them home.

Pretty funny actually, if you were not involved...

Which
implies a mindset that would prefer to see the oxides scraped off the
platters and reduced to metal, while the platters are melted down and
cast into truck wheels.

Truck wheels? No. Too insecure. They should be fired into the Sun!
Of course then somebody could intercept them on the way. Hmmmm. Stored
in a reactor core, maybe?

Arno

 

[Arno Wagner]

Fascinating thread. However, this Seagate "encryption" will be broken
within days by some Russian or Chinese IT guru. Perhaps hours. Dare
say I might even be able to do it myself.

The only encryption I trust is that delivered by means of a steel
hammer.

Oh, (disk) encryption can be done right and be pretty hard or even
impossible to break. But it is hard to get it right. And then it
will be inconvenient and either slow things down or make them more
expensive. These commercial systems, also for memory sticks, are often
not more than a password check tied into the driver software or
hardware somewhere. Usually you can circunvent them just by reading
the surface or storage chip directly. Even easier breaks may exist.

Arno

 

[Paul Rubin]

I agree to what you say. But my impression is that it is not a S/N
issue at all, the data on the disks is all the surface can take.
Residual older bits are erased completely by the new data.

As Lou Scheffer on sci.crypt put it,

The disk drive makers have to include engineering margin. The
data might be written when the drive is cold, and must be readable
when the drive is hot. The servo might be tracking a few nm
towards the center when writing, and a few nm towards the edge
when reading. The drive might be subject to vibration (say in a
car or plane) which the servos cannot completely eliminate. The
data must be readable a few years later, after the circuits have
aged and drifted. If disk drives are like most electronics, a
factor of 2 for all these combined would not be unusual.

This makes sense to me.

Google-groups is great! I have an occasional look into sci.crypt,
but stopped reading it regularly a long time ago. Too low
S/N ratio...

It's not bad once you've gotten to categorize the different posters
and developed a kill file. There are some well informed people there
who manage to carry on interesting discussions through all the noise.
In that particular thread the posts of Bryan Olson, Lou Scheffer
(displayed as (e-mail address removed)), and Rob Warnock are especially
interesting. Rob posted a link to this thesis about disk drive data
encoding:

http://vivaldi.ucsd.edu:8080/~kcheng/thesis/thesis.pdf

I don't think actual drives are using anything that advanced yet though.

 

[Timothy Daniels]

As Lou Scheffer on sci.crypt put it,

The disk drive makers have to include engineering margin. The
data might be written when the drive is cold, and must be readable
when the drive is hot. The servo might be tracking a few nm
towards the center when writing, and a few nm towards the edge
when reading. The drive might be subject to vibration (say in a
car or plane) which the servos cannot completely eliminate. The
data must be readable a few years later, after the circuits have
aged and drifted. If disk drives are like most electronics, a
factor of 2 for all these combined would not be unusual.

This makes sense to me.

In other words, it takes multiple random data overwrites to lose
the original data down in the noise, and there is "slop-over" between
tracks. Are you taking notes, Arno?

*TimDaniels*

 

[Paul Rubin]

In other words, it takes multiple random data overwrites to lose
the original data down in the noise, and there is "slop-over" between
tracks. Are you taking notes, Arno?

I did a calculation in the sci.crypt thread indicating that the
slop-over is useless for data recovery.

 

[Timothy Daniels]

I did a calculation in the sci.crypt thread indicating that the
slop-over is useless for data recovery.

Interesting. Were you assuming that the original data
and the overwrite data were both done with the same
write head? (Admittedly a good assumption for most
modern hard drives; not so good for removable media
drives.) Were you assuming that the oxide layer's
magnetization curve or the optical pigmentation's
darkening curve was linear?

*TimDaniels*

 

[Paul Rubin]

Interesting. Were you assuming that the original data
and the overwrite data were both done with the same
write head? (Admittedly a good assumption for most
modern hard drives; not so good for removable media
drives.) Were you assuming that the oxide layer's
magnetization curve or the optical pigmentation's
darkening curve was linear?

AFAIK there is no oxide on hard disk platters any more. That went out
with stone knives and bearskins. The calculation assumed simply that
1) the original data rate came within 5 db of the Shannon limit for
the read channel; 2) the "slopover" energy was 10 db below the
original complete signal's. Nothing about magnetization curves.

 

[Odie Ferrous]

AFAIK there is no oxide on hard disk platters any more. That went out
with stone knives and bearskins. The calculation assumed simply that
1) the original data rate came within 5 db of the Shannon limit for
the read channel; 2) the "slopover" energy was 10 db below the
original complete signal's. Nothing about magnetization curves.

You guys are getting *scarily* close to something that's been kept top
secret for a few years. Perhaps you should get together some time.

I have to remain in the dark...

Fortunately, this is all well beyond our resident genius' scope of
(dis)abilities.


Odie

 

[Timothy Daniels]

The calculation assumed simply that
1) the original data rate came within 5 db of the
Shannon limit for the read channel;

Why so fast?

2) the "slopover" energy was 10 db below the
original complete signal's.

Why only 10dB?

Nothing about magnetization curves.

How about residual transverse magnetization
between sequential bits? (Magnetic lines follow
circuitous paths, so they don't end at the end of
a bit but continue back to the bit's starting point.)

Did you consider magnetic bubbles being
driven deeper into the medium by subsequent
writes?

IOW, did you consider the physics of the situation
as well as the mathematics?

*TimDaniels*

 

[Odie Ferrous]

Why so fast?


Why only 10dB?


How about residual transverse magnetization
between sequential bits?

You're so close...


Odie

 

[Arno Wagner]

As Lou Scheffer on sci.crypt put it,

The disk drive makers have to include engineering margin. The
data might be written when the drive is cold, and must be readable
when the drive is hot. The servo might be tracking a few nm
towards the center when writing, and a few nm towards the edge
when reading. The drive might be subject to vibration (say in a
car or plane) which the servos cannot completely eliminate. The
data must be readable a few years later, after the circuits have
aged and drifted. If disk drives are like most electronics, a
factor of 2 for all these combined would not be unusual.

This makes sense to me.

It really depends on the actual material properties. My impression
is that this is mor of a stepped process, were you cannot have
magnetic zones a few nm large, since they would not be stable.

It's not bad once you've gotten to categorize the different posters
and developed a kill file. There are some well informed people there
who manage to carry on interesting discussions through all the noise.
True.

In that particular thread the posts of Bryan Olson, Lou Scheffer
(displayed as (e-mail address removed)), and Rob Warnock are especially
interesting. Rob posted a link to this thesis about disk drive data
encoding:

I don't think actual drives are using anything that advanced yet though.

I think I will give sci.cryp another try. Thanks for the info.

Arno

 

[Arno Wagner]

AFAIK there is no oxide on hard disk platters any more. That went out
with stone knives and bearskins.

And the steppers. Oxyde cannot hold todays data densities.

The calculation assumed simply that
1) the original data rate came within 5 db of the Shannon limit for
the read channel; 2) the "slopover" energy was 10 db below the
original complete signal's. Nothing about magnetization curves.

These numbers seem reasonable to me. If the margins were much larger,
HDD manufacturers could move tracks closer together....

Arno

 

[Paul Rubin]

Why so fast?

This appears to be well within the capability of today's technology.

Why only 10dB?

If it were more than 10 db it would make the problem even harder.

How about residual transverse magnetization
between sequential bits?

There are no "sequential bits" on a modern hard drive. I think you're
imagining something like 1980's disk technology, where there were
actual bits on the disk (in the sense of physical regions whose
magnetnetization gets interpreted as 1 or 0). It's not done that way
any more. They instead demodulate the analog signal coming back from
the disk head something like the way a high speed dialup modem does,
using soft-decision convolutional codes, as compared with the old 300
baud modems that just did frequency shift keying. The 537th bit of
your file might be a one or a zero, but there's no specific place on
the disk you can point to and say that's where that bit is stored.

Did you consider magnetic bubbles being driven deeper into
the medium by subsequent writes?

I simply postulated that all effects like that were included in the
"slopover" and that the total of all of them was >= 10 db below
the original signal.

IOW, did you consider the physics of the situation
as well as the mathematics?

Only the way I stated.

 

[Timothy Daniels]

There are no "sequential bits" on a modern hard drive....
They instead demodulate the analog signal coming back from
the disk head... ,
using soft-decision convolutional codes, .....
...there's no specific place on the disk you can point to and
say that's where that bit is stored.

Hysteresis and subsurface domains must make for
interesting hunting grounds. I wonder what light acid
etching would do.

*TimDaniels*

 

[John Doe]

Rod Speed is an insulting tough guy wanna-be troll.

See also:
"JohnH" <johnh jjss.com>
"Oscar Jones" <oj ojqw.com>
"Rod Speed" <rod.speed.aaa gmail.com>


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From: "Rod Speed" <rod.speed.aaa gmail.com>
Newsgroups: comp.sys.ibm.pc.hardware.storage
Subject: Re: Wiping a hard drive?
Date: Mon, 23 Oct 2006 04:50:45 +1000
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Arno Wagner wrote

the U.S. Department of Defense, I have read in several
magazine articles over the years, requires a minimum
number of random data overwrites, not just one overwrite,
and not the same data over and over.

Irrelevant to what is actually required. That is just a belt and
braces approach which can be justified when its only done
very rarely and the data is very important. That is never true
with the average personal PC, even one used in business.

The reason is that not all the magnetic domains are set or re-set on a write, and some of them
remain in the original orientation.

Doesnt matter.

Sophisticated intrumentation can ignore the strong overwrite data if it knows what it will be and
then just read the weak background signal from the overwritten data.

Easy to claim, child.

The key is knowing what the overwrite data is - which consistent overwriting provides. The
difficulty is then increased when the overwrite data is unpredictable.

Easy to claim, child. Not a shred of evidence that its even possible.

Of course, one could read the overwrite data and then go back and filter that out of the overall
signal, and that is the reason for multiple overwrites -
Nope.

at some point it becomes impossible to determine
which level of overwrite is being read, and one can't tell
which data was the original - it all becomes just noise.

Easy to claim, child.

So, for less than "national technological means", multiple
overwrites with random data will hide the underlying data.

Just as true of a single pass of zeros too.

Of course, "national technological means" are not described for everyone to read, but I have read
that there is some slop-over in bit magnetism that reaches outside the normally readable data
tracks.

Some fools claim that the CIA executed Kennedy too.

'I have read' cuts no mustard, child.

Also, there can be variances in placement of write heads in normal manufacturing and also due to
normal wear.

Wrong with servo drives, and they are all servo drives now.

If the overwriting was not done with the same write head that wrote the original data,

There isnt any other possibility, stupid.

the slop-overs will have different placement,

Only in your pathetic little pig ignorant fantasyland.

and the original data slop-over can be distinguished from the overwrite data's slop-over.

Only in your pathetic little pig ignorant fantasyland.

In normal practice, though, multiple random data overwrites should suffice to hide any sensitive
data.

Single zero data overwrite is suffice to hide any sensitive data.

How MANY overwrites? Mmmmm..... *I'd* use three.

And that number is plucked from your arse, as always.

 

[Rod Speed]

This desperately cowering gutless ****wit is a desperately
cowering gutless ****wit that cant even manage to work
out something as basic as what a monopoly actually is.

 

[Aidan Karley]

As soon as it is known to be compromised, the channel will
be abandoned and surveilance of it will become ineffective.

s/known/suspected
("substitute the string 'suspected' for occurrences of 'known'")