Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!rutgers!ames!ucbcad!ucbvax!cbosgd!ihnp4!cuuxb!dlm
From: dlm@cuuxb.ATT.COM (Dennis L. Mumaugh)
Newsgroups: sci.crypt
Subject: Re: Erasing magnetic media
Message-ID: <1384@cuuxb.ATT.COM>
Date: Fri, 6-Nov-87 10:44:16 EST
Article-I.D.: cuuxb.1384
Posted: Fri Nov  6 10:44:16 1987
Date-Received: Tue, 10-Nov-87 07:10:09 EST
References: <7566@reed.UUCP> <1175@cup.portal.com> <1945@crash.CTS.COM>
Reply-To: dlm@cuuxb.UUCP (Dennis L. Mumaugh)
Organization: ATT Data Systems Divison, Lisle, Ill.
Lines: 50

In article <1945@crash.CTS.COM> ag@crash.CTS.COM (Keith Gabryelski) writes:
>In article <1175@cup.portal.com> Kenneth_R_Jongsma@cup.portal.com writes:
>>Others may be interested.... The actual requirement is that the media
>>be written with at least 100 alternating 1/0 bits. i.e 11111 00000 11111,
>>etc...  Some media cannot be declassified. If memory serves, the old (still
>>in use in the Minuteman system) core memory had to be destroyed.
>
>I am interested in 'Why' 100 alternate 1/0 writes will not declassify some
>media.  It seems to me that after 5 or so random 1/0 writes the original
>data would be so far gone that retreival by any means is impossible.
>
>Enlighten me.
>
Having a modest part in the original decisions that  lead  up  to
the policy I will attempt to answer .....

Way back when, our group had a problem with  computers  that  ran
classified  programs (and with classified data).  What to do with
the defective memory which  in  those  days  were  magnetic  core
based.

Certain studies said [ deleted ] ....

So the final policy was that if one over wrote the data with  100
cyles of ones and zeros (alternating) any data would be so buried
in the ramdom molecular noise that ....  This  was  for  magnetic
cores.  Similar behavior was approved for tapes using VERY strong
degaussing methods.

But then some one asked the question: "That means  I  could  mail
the  tape  to  the  Russian Embasy, then?" And the powers that be
looked  pale.  So,  the  compromise  was  reached:  treat  it  as
unclassified but don't EVER let it leave safe handling.

The effect  was  to  allow  it  to  be  handled  administratively
unclassified and stored that way.

But when sending a tape out of the "compound"  one  must  certify
that the tape has NEVER had any classified data on it.  Hence our
penchant for sacrificing virgins [tape that is] to the computer.

Disks are a diferent story as the write heads tend  to  splatter.
Also only certain tape degaussers are approved.

BTW:  I once did  send  some  one  a  tape  and  they  were  VERY
disappointed  that  it  wasn't  used,  with intereresting goodies
following the two tape marks.
-- 
=Dennis L. Mumaugh
 Lisle, IL       ...!{ihnp4,cbosgd,lll-crg}!cuuxb!dlm