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Re: Default number of overwrites in shred
From: |
Jim Meyering |
Subject: |
Re: Default number of overwrites in shred |
Date: |
Sat, 05 May 2007 00:45:00 +0200 |
Paul Eggert <address@hidden> wrote:
> Jim Meyering <address@hidden> writes:
>
>> I too would feel better with a minimum of 2 or 3 passes, just in case.
>
> If we want to be conservative, then the U.S. Defense Security
> Service's Clearing and Sanitization Matrix (2005-06-27)
> <http://www.dss.mil/isp/odaa/documents/clearing_and_sanitization_matrix.pdf>
> specifies the following methods for rigid disk:
>
> * For clearing, "Overwrite all addressable locations with a single character."
>
> * For sanitization, "Overwrite all addressable locations with a
> character, then its complement. Verify 'complement' character was
> written successfully to all addressable locations, then overwrite
> all addressable locations with random characters; or verify third
> overwrite of random characters. Overwrite utility must write/read
> to 'growth' defect list/sectors or disk must be mapped before
> initial classified use and remapped before sanitization."
>
> Oh, and big print above it, "THIS METHOD NOT APPROVED FOR SANITIZING
> MEDIA THAT CONTAINS TOP SECRET INFORMATION." (Just thought you'd
> like to know: the DoD requires degaussing or destruction instead,
> for top-secret disks. Also, shredding does not count as
> destruction: you have to disintegrate, incinerate, pulverize, or
> melt)
>
> Anyway, 'shred' currently does the first, but not the second, as it
> doesn't verify what it's written. That should get fixed, no?
I agree.
> How about this idea, to get 'shred' to conform to DoD 5220 rules
> for sanitization for classified (but not top secret) disks?
>
> Change the default number of passes to 4.
>
> If the number of passes is 4 or more, then use these three passes
> first:
>
> * Write all 1s.
> * Write all 0s.
> * Verify that all 0s were written.
>
> After that, do N - 3 passes the way that 'shred' already does them
> (except omit the all-1s and all-0s passes). This would suffice for
> sanitization.
>
> Pass 3 requires read access to the file, which 'shred' currently
> doesn't do. I suggest that we require read access to the file; I have
> some qualms about shredding something I can't see.
Yes. Same here.
I like your plan.
- Re: Default number of overwrites in shred, (continued)
Re: Default number of overwrites in shred, Paul Eggert, 2007/05/03
- Re: Default number of overwrites in shred, Peter Eckersley, 2007/05/03
- Re: Default number of overwrites in shred, Jim Meyering, 2007/05/04
- Re: Default number of overwrites in shred, Peter Eckersley, 2007/05/04
- Re: Default number of overwrites in shred, Jim Meyering, 2007/05/04
- Re: Default number of overwrites in shred, Paul Eggert, 2007/05/04
- Re: Default number of overwrites in shred,
Jim Meyering <=
- Re: Default number of overwrites in shred, Peter Eckersley, 2007/05/04
- Re: Default number of overwrites in shred, Philip Rowlands, 2007/05/05
- Re: Default number of overwrites in shred, Pádraig Brady, 2007/05/06
- Re: Default number of overwrites in shred, Paul Eggert, 2007/05/08
Re: Default number of overwrites in shred, John Cowan, 2007/05/04
Re: Default number of overwrites in shred, Peter Eckersley, 2007/05/04