Re: How many overwrites for secure erase?

"Sebastian G." <seppi@xxxxxxxxx> writes:

bealoid wrote:

Rick Merrill <rick0.merrill@xxxxxxxxxxxxxxxx> wrote in
news:JrKdndJ_eYM6A1nanZ2dnUVZ_oDinZ2d@xxxxxxxxxxx:

[snip]

For you and I (assuming You're not a spy) a single overwite is
quite enough - to get stuff off it requires extreme measures.

Here's the thing: What attacks exist to recover data over-written just once
with a bunch of 0 bits?


A very simple one:

1. read the data as a analogue signal

How?
2. interpret the signal as digital signal
3. calculate the ideal analogue signal that represents these digital data
4. calculate the difference between the two, the result is the overlap of
the previous signal(s) and noise
Yes, noise dominates.
(5. repeat)

What good does that do. The noise is there on the platter And because of
the very complex data encoding that "signal " has only an indirect
relation to the actual data.

No company (AFAIK) will recover data overwritten like that.


AFAIK many companies actually offer this procedure if more trivial measures
fail, but for a horrible price.

Perhaps you could tell us some, and tell us how you know they offer this
service.


So now the attack model has to assume exotic alien tech.


The above is not alien. However, the success rate with modern hard drives
should be in the dimension of 1%, that is they'll recover each bit correctly
with a chance of 51%, 1% different from pure guessing (which is still
statistically significant).
.

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