From owner-freebsd-security  Tue Jun 29  4:15:43 1999
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Date: Tue, 29 Jun 1999 13:15:29 +0200
From: Eivind Eklund <eivind@FreeBSD.ORG>
To: Wes Peters <wes@softweyr.com>
Cc: cjclark@home.com, FreeBSD Security <freebsd-security@FreeBSD.ORG>
Subject: Re: Secure Deletion
Message-ID: <19990629131529.A61249@bitbox.follo.net>
References: <199906250212.WAA07810@cc942873-a.ewndsr1.nj.home.com> <3773F67A.CC9B6215@softweyr.com>
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In-Reply-To: <3773F67A.CC9B6215@softweyr.com>; from Wes Peters on Fri, Jun 25, 1999 at 03:36:58PM -0600
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On Fri, Jun 25, 1999 at 03:36:58PM -0600, Wes Peters wrote:
> This won't do it, if you're really interested in obliterating the file 
> contents.  What you want to do is overwrite the file blocks with 
                                                  ^^^^
disk

> alternating patterns of 10101010 then 01010101 at least 100 times.  
> Due to the way modern recording formats work, and the memory of the 
> cells that actually store the bits on the disk, anything less won't 
> really erase the disk.

More or less correct.  There are a lot of details to this, and just
writing 0x55/0xaa as normal data values won't make them hit the disk
that way.

Since what I have to write about this topic would just end up being a
paraphrase of what Peter Gutmann has to say, I suggest you read the
paper he presented at Usenix 1996:
	http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html

Eivind.


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