[cryptography] Deleting data on a flash?

[Eugen Leitl]

----- Forwarded message from Moritz <moritz at headstrong.de> -----

Date: Mon, 23 Sep 2013 10:26:42 +0200
From: Moritz <moritz at headstrong.de>
To: cryptography at randombit.net
Subject: Re: [cryptography] Deleting data on a flash?
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On 09/23/2013 10:02 AM, ianG wrote:
>> The issue is that it's pretty much impossible to delete data securely
>> from a flash device.
> Why is that?

The flash memory controller hides the real storage cells from you and
spreads writes across all cells equally for wear-leveling. You cannot
directly access the cells. Some SSDs have a secure erase option, but you
never know if it is properly implemented, and you can only use it to
wipe the complete drive.

https://www.schneier.com/blog/archives/2011/03/erasing_data_fr.html

[...] Our results lead to three conclusions: First, built-in commands
are effective, but manufacturers sometimes implement them incorrectly.
Second, overwriting the entire visible address space of an SSD twice is
usually, but not always, sufficient to sanitize the drive. Third, none
of the existing hard drive-oriented techniques for individual file
sanitization are effective on SSDs.

--Mo
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Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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