On Apr 28, 2008, at 23:56, Perry E. Metzger wrote:

If you have a rotten apple engineer, he will be able to hide what he's
trying to do and make it look completely legit. If he's really good,
it may not be possible to catch what he's done EVEN IN PRINCIPLE.

Fred Cohen proved in 1984 in his "Computer Viruses, Theory and Experiments"[1] that "Program P is a virus" is undecidable. I assume that this result can be applied to hardware in the form that "Chip C contains malicious gates" is also undecidable. (Caveat: Cohen seems to make the fundamental assumption that there is no fundamental distinction between code and data, something that need not necessarily hold everywhere inside a computer chip.)



[1] See for example http://vx.netlux.org/lib/afc01.html

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