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From: outer@utcsrgv.UUCP (Richard Outerbridge)
Newsgroups: net.crypt,net.micro
Subject: Software Piracy and Coupons
Message-ID: <2557@utcsrgv.UUCP>
Date: Mon, 24-Oct-83 17:22:22 EDT
Article-I.D.: utcsrgv.2557
Posted: Mon Oct 24 17:22:22 1983
Date-Received: Mon, 24-Oct-83 17:40:09 EDT
Organization: CSRG, University of Toronto
Lines: 19

See SCIENCE, Volume 221, No. 4617, p1279, 21 September 1983
"Scheme to Foil Software Pirates"
	The article describes a new method of protecting floppy-disk
software developed by Adi Shamir and called "...a very clever idea" by
Ronald Rivest.  The manufacturer uses specially-modified disk drives to put
"soft" bits on his disks (bits that a normal drive cannot reliably read)
and the program when executing reads the special tracks to make sure
that the bits ARE unreliably recorded.
	The trick is that if the disks are copied the "soft" bits will
become random "hard" bits (because normal disk drives only write
unambiguous bits).  The copied program will detect that the "coupon"
tracks have become certain, and can take evasive action.  What's more,
the original program can selectively write over the "coupon" tracks
(again, resulting in unambiguous bits) and so keep count of the number
of times the program has been used; like a postage meter, when all or
most of the "soft" bits have become "hard", the program can "expire".
	Neat, huh?

csrgv!outer	@ U of Toronto CSRG