Re: Clever ways to hide a compare
- From: "David J. Craig" <spamtrap@xxxxxxxxxx>
- Date: Sun, 25 Sep 2005 01:16:49 +0000 (UTC)
Depending upon the register/data size, you can use a subtract, add,
multiply, or divide. You can do a translate and come up with some
interesting possibilities. If this is DOS and not Windows NT, you can have
self modifying code that can do wonderful things. Translate an instruction
to something good if the value is good. Otherwise change it to something
that will lead to headaches.
"jonathon" <spamtrap@xxxxxxxxxx> wrote in message
news:1127603005.082317.85010@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> Suppose you are writing a protection scheme, and need to compare 2
> values. Is there a clever way to do this without an outright 'cmp'
> instruction? Of course it's always possible to use the value in a
> calculation that is needed for correct functionality of the program,
> but I was wondering if there is a way to have 2 values compared in a
> sneaky way where it is not immediately evident what is happening.
>
.
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