Reverse engineering CRC?

Gregory Ewing greg.ewing at
Mon Mar 8 23:16:24 CET 2010

Dave Angel wrote:
> If you know so little about the 
> value, how do you even know it's a CRC ?  Could it be a ones-complement 
> sum, such as used in Ethernet?

I'm going by the fact that the application reports a
"CRC mismatch" when it's wrong. I can't be sure that what
it calls a "CRC" is really a true CRC, but it's more than
a simple sum, because changing one bit in the file results
in a completely different value.

> Is the problem really worth it?

Probably not -- it looks like fixing the problem I'm trying
to fix by hand will be faster in the long run. I just thought
it might turn out to be a solved problem and someone could
point me to an algorithm for it, but it seems not.


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