looking for anti-tamper software

I used to have this C source that I could embed in a program, and it
would tell me if the software had been tampered with at runtime.  I've
lost/mislaid/whatever the source, and I was wondering if anyone had anything
that would do the same thing.  As I recall, it calculated a simple CRC and
embedded it into the .EXE file (it was written for MS-DOS).

It doesn't need to be cryptographically secure - I just need to check to see
if the executable has been corrupted.  I've leafed through alt.sources and
comp.sources.*.

Thanks in advance...
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> 
> I used to have this C source that I could embed in a program, and it
> would tell me if the software had been tampered with at runtime.  I've
> lost/mislaid/whatever the source, and I was wondering if anyone had anything
> that would do the same thing.  As I recall, it calculated a simple CRC and
> embedded it into the .EXE file (it was written for MS-DOS).
> 
> It doesn't need to be cryptographically secure - I just need to check to see
> if the executable has been corrupted.  I've leafed through alt.sources and
> comp.sources.*.

You are aware that there is a generic attack against all such defenses -
aren't you? It has been published for 7+ years.  For details see:

	A Short Course on Computer Viruses - Wiley and Sons - 94

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