Re: Innocent Download of kp

"MM" <kylix_is@xxxxxxxxxxx> wrote in message
news:74jvt3pmu5ktphtq11g3781fqq5fakias7@xxxxxxxxxx
On Tue, 18 Mar 2008 12:31:23 -0000, "M.I.5¾"
<no.one@xxxxxxxxxxxxxxxxxxxxxx> wrote:

As said elswhere, GCHQ claim to be able recover even multiply overwriten
data. It is the nature of that organisation that they can almost
certainly
accomplish much beyond what they claim and would never publish their real
capability.

Think about what you're saying: A drive manufacturer (who knows as
much as is possible to know about their own designs) could, if your
supposition were true, increase the capacity of their products by -
what? - five-fold? Ten-fold? A hundred-fold? By adopting the same
technology. At what point does the GCHQ "magic" cease to function? I
mean, if data can be continually written to a drive, then erased, then
retrieved and the cycle repeated ad infinitum, one would hardly ever
need to buy bigger drives.

I think you are taking things to extremes. Data recovery on modern drives
can recover a lot of overwritten data but it is by no means infallible and
the probability of recovery of a cluster decreases with every overwrite.
Continual overwrite as mentioned above is not possible but then I assume you
are using hyperbole. A text only medium like this does not lend itself to
subtlety of language so apologies if I picked you up wrong.

The problem is one of economy of scale.
It is possible to squeeze more data density from existing hard drives but
the precision of head placement and sensitivity of the head required would
increase the cost beyond that that the market will bear.

To give you an analogy. For christmas I was given a set of UK road maps. It
was a gimmicky thing, they were on small cards (about half postcard size)
and needed a cheap viewer to see them. fairly useless to be honest.
Printing density would permit more detail to be printed on the map but then
I would need a good quality lens to see more. A greater print density would
require compound lenses. The limiting factor is that the better lenses would
make the thing cost more than the £9.99 price and therefore probably price
it out of the market.

Track-edge recover is like like following car tracks in the snow. A lane can
be 3 times the width of a car and if a car makes a set of tracks in virgin
snow it is possible to read those tracks even after many cars have passed by
as they will not always travel on the same part of raod. If the inital car
travelled for some of the time in the centre then the tracks will be lost
but if it travelled at the edge then it may be readable for some time.

Data density limit of a standard drive is limited by the theoretical
magnetic data density limit of the platter (always much higher then the
actual density), the width and strength of the write mechanism, the
sensitivity of the read mechanism and the accuracy of the head placement
mechanism.
It is possible to have much higher data density on the same medium if we use
narrow, powerful, sensitive & focussed heads with a very accurate placement
system but they would cost a fortune.

To push the car and road analogy it is possible to increase the traffic flow
by narrowing lanes on a motorway and squeexe in and extra lane, narrow the
gaps between cars and increase the speed but it would require far more
expensive cars with auto steer and convoying ability. This technology does
exist but is not commercially viable yet although I think BMW has tested
auto-convoying.
Pretty crappy analogy but I hope it illustrstes a point

As HDD technology advances data recovery does become harder and harder as
commercial quality closes the gap on cutting-edge 'military' quality

However. The data recovery 'legend' being pushed by GCHQ, media etc is far
greater than reality but it does pay to advertise and scare the target
audience.

I recall posting a long and boring post about how even precisely
head-aligned overwritten data can be read some weeks ago. It should be on
googlegroups somewhere. This is possible but needs very specialised kit as
the platters get removed, placed in a reader with very very precise head
placement and much more sensitive heads and some fancy signal processors.
It can recover overwritten data but 100% is unlikely and hugely expensive.
It is the kind of thing that I would expect would be done on stolen hard
drives from foreign governments or known terrorist cells (which is the
stock-in-trade for GCHQ) rather than trawling for KP.

Andy


.

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