[Cryptography] Crypto Trick Makes Software Nearly Impossible to Reverse-Engineer

[Jon Callas]

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On Feb 12, 2015, at 6:27 PM, Peter Gutmann <pgut001 at cs.auckland.ac.nz> wrote:

> This looks like a modern update of an old trick from the late 1908s/early
> 1990s, you set the trap bit on the CPU and decrypt each instruction before
> it's executed, then re-encrypt it afterwards.  Unfortunately this only worked
> under DOS, as soon as protected-mode anything came along (e.g. a DOS box under
> Windows 3.1), it didn't work any more (or at least I couldn't be bothered
> trying to figure out what was required).  The downside was that it made
> execution really, really slow, but if you ran just a few core bits of code
> that way then it was manageable.

It also reminds me of a thing Intel did in the late '90s, as well. There was also a published paper on it in, I believe one of the early Information Hiding workshops.

	Jon


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