full-disclosure - Re: Disk wiping -- An alternate approach?

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Message-ID: <61414d3f1001260828m344008f4q613d046610bd9d8a@mail.gmail.com>
Date: Tue, 26 Jan 2010 17:28:01 +0100
From: "E. Prom" <e3prom@...il.com>
To: full-disclosure <full-disclosure@...ts.grok.org.uk>
Subject: Re: Disk wiping -- An alternate approach?

2010/1/26 Michael Holstein <michael.holstein@...ohio.edu>:
>> By the way, does somebody knows about the flash memory?
>> Is zeroing a whole usb key enough to make the data unrecoverable?
>>
>
> No, wear-leveling (done at the memory controller level) will dynamically
> re-map addresses on the actual flash chip to ensure a relatively
> consistent number of write cycles across the entire drive.

Agreed, if I want to delete one file : the file will be unlinked and
the zeroes will be written somewhere else. But what if I zero the
whole memory, with something like dd if=/dev/zero
of=/dev/disk/by-id/my_flash_device? Whatever the order and places the
zeroes are written, in the end there should be zeroes everywhere.
Unless there is more blocks on the chip than it reports having, or
some compression is used where instead of "00...0" it would write "0
from adress 1 to last address". I'm just speculating...

> The only way to completely "wipe" a flash disk is with a hammer.

That's the only reliable way, but a convenient way to erase data
before lending a usb key would be nice.

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