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From: bdugan@teri.bio.uci.edu (Bill Dugan)
Newsgroups: comp.sys.mac.programmer,comp.protocols.appletalk
Subject: Re: Idea for painless copy protection
Summary: Appletalk copy protection = easiest to crack
Message-ID: <27A3555F.13566@orion.oac.uci.edu>
Date: 27 Jan 91 22:34:07 GMT
References: <1991Jan27.144523.20674@phri.nyu.edu> <1991Jan27.214310.3870@agate.berkeley.edu>
Reply-To: Bill Dugan <bdugan@teri.bio.uci.edu>
Organization: University of California, Irvine
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Nntp-Posting-Host: teri.bio.uci.edu

In article <1991Jan27.214310.3870@agate.berkeley.edu> lippin@math.berkeley.edu writes:
>Recently roy@alanine.phri.nyu.edu (Roy Smith) wrote:
>>	When the program starts up, it installs something which listens for
>>broadcast packets to a specific port (my knowledge of appletalk is sketchy,
>>but this is easy to do in IP and I'm assuming AT has some similar
>>mechanism).  The program then sends out a broadcast packet to that port and
>>listens for any responses.  The responses it would get back would contain
>>the serial number of other copies of the program installed elsewhere on the
>>same AT network.  If any S/N matched that of this copy, it would refuse to
>>run.
>
>[...]
>There are problems, however.  A legitimate user may be unable to start
>the program because someone else is running with his serial number.
>On a large network, it may be difficult to track down the offender.
>
>Network managers must keep track of where all the serial numbers are
>being used -- if one copy is destroyed, they have to reinstall it with
>the right serial number.

Another problem, of course, is that this type of copy protection is
very easy to crack.  All you have to do is write an INIT that patches
the AppleTalk send calls; just kludge it to search for search string n
that is made by the copy-protected application, and change a couple
chars, and suddenly you have a request that nobody will respond to.
As a network manager, if I were confronted with the necessity of keeping
track of 400 copies of a program with all the serial numbers, I would
seriously consider investing time in such a hack.

bill