Reverse engineering CRC?

Dave Angel davea at ieee.org
Mon Mar 8 11:13:09 CET 2010


Steven D'Aprano wrote:
> On Mon, 08 Mar 2010 16:09:12 +1300, Gregory Ewing wrote:
>
>   
>> Given some known data/crc pairs, how feasible is it to figure out the
>> polynomial being used to generate the crc?
>>     
>
> Google is your friend:
>
> http://www.woodmann.com/fravia/crctut1.htm
>
>   
That page was interesting to read, especially since I've implemented the 
three algorithms - CRC16, CRC32, and the reversed version of CRC16, all 
in the long-distant past.

However, if there's anything in there about how to derive the polynomial 
algorithm from (a few) samples I missed it entirely. Instead, what it 
calls reverse engineering is figuring out how to modify a message to 
force it to have a desired CRC value (when the CRC polynomial is already 
known).

DaveA




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