Re: getting around Ken Thompson's compiler Trojan

From: Barry Margolin (barmar@genuity.net)
Date: 01/28/03 

From: Barry Margolin <barmar@genuity.net>
Date: Tue, 28 Jan 2003 00:45:24 GMT

In article <b14bib$tqk$1@atlas.dgp.toronto.edu>,
Alan J Rosenthal <flaps@dgp.toronto.edu> wrote:
>If you know the "is this the compiler" algorithm, you can come up with a
>transformation on the compiler source code which fools it. It needn't be as
>sophisticated as a general-purpose obfuscator.
>
>If you _don't_ know the "is this the compiler" algorithm, you _can't_ come
>up with a transformation on the compiler source code which is guaranteed to
>fool it, said transformation being your obfuscator or any other algorithm
>or hand-implemented tweak.

And if you can make an educated guess of the algorithm, you have a good
shot at coming up with a transformation.

BTW, not only does the compiler have to recognize itself, but it also has
to recognize the login program, so it can reinsert the backdoor. 

-- 
Barry Margolin, barmar@genuity.net
Genuity, Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

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