Path: utzoo!mnetor!uunet!husc6!tut.cis.ohio-state.edu!osu-cis!att-cb!clyde!rutgers!iuvax!pur-ee!uiucdcs!uiucdcsp!gillies
From: gillies@uiucdcsp.cs.uiuc.edu
Newsgroups: comp.sys.mac
Subject: Re: Virus on the Mac?
Message-ID: <76000159@uiucdcsp>
Date: 20 Mar 88 03:57:00 GMT
Lines: 34
Nf-ID: #R:<IWAi9Vy00V4-Frk0Td@andrew.cmu.e:-35:uiucdcsp:76000159:000:1662
Nf-From: uiucdcsp.cs.uiuc.edu!gillies    Mar 19 21:57:00 1988


Trojan Horses are a classic problem in the discipline of operating
system protection.  Any partial solution to this problem DOES NOT
depend on whose processor chip you buy.  It depends on having a
serious protection scheme built by a designer that expressly solves
the problem.

Theoretically, whether a program halts and zeroes core is
undecideable.  Therefore, it is certainly undecideable whether a
program halts and does a bad thing XYZ (in particular, XYZ = zeroing
core) to your computer.

You can protect against a Trojan Horse, but you cannot completely
prevent one (assuming you load new software into your computer).  To
protect against one, you need to confine untrusted software.  In
principle, you must confine each piece of software FOREVER.  If the
program writes to the disk, the objects it must access (to do useful
work) will always be in peril.

If the software spoofs you successfully (e.g. "This piece of software
is a univeral vaccine INIT -- it needs FULL access to your system
file", or "This piece of software patches your system file with a new
version of Quickdraw that is 5 time faster!"), and you believe this
nonsense, then you're sunk.  Your only hope is to disassemble the code
an prove (theoretically) that the program does nothing harmful.

Sorry to bring you this depressing news....

Don Gillies {ihnp4!uiucdcs!gillies} U of Illinois
            {gillies@p.cs.uiuc.edu}
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Doing an M.S. thesis in protection.  Did a B.S. thesis in protection.
Hope I don't have to do a Ph.D. in protection.
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