# Re: How many overwrites for secure erase?

*From*: "Sebastian G." <seppi@xxxxxxxxx>*Date*: Fri, 29 Feb 2008 00:47:39 +0100

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

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

(5. repeat)

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.

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).

.

**Follow-Ups**:**Re: How many overwrites for secure erase?***From:*Unruh

**References**:**How many overwrites for secure erase?***From:*Arthur T .

**Re: How many overwrites for secure erase?***From:*David H. Lipman

**Re: How many overwrites for secure erase?***From:*Unruh

**Re: How many overwrites for secure erase?***From:*Moe Trin

**Re: How many overwrites for secure erase?***From:*David H. Lipman

**Re: How many overwrites for secure erase?***From:*Moe Trin

**Re: How many overwrites for secure erase?***From:*Rick Merrill

**Re: How many overwrites for secure erase?***From:*bealoid

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