On 01/27/2020 02:20 AM, Mattis Lind via cctalk wrote:
Yes, there are the crc reveng for example. But I cannot get it to generate
the CRC digits that matches. Neither does it give me anything when I ask it
to search for algorithm used.
Of course it is probably just me that don't understand it well enough.


Soem years ago I needed to crack the CRC on a Fanuc serial encoder. Luckily, the CRC value was just 5 bits. I built a device to read out and store the data from the encoder on a PC. Then, I wrote a little c program that had a "universal" CRC implementation, where the polynomial was supplied as a command line parameter. It would read the stored file, apply the polynomial as given and report the residuals. With just a 32 value search space, I just entered them one at a time, and a few minutes later, I had found the polynomial that gave all zero residuals.

With a larger search space, you might construct such a program and let it run all possible polynomial values and report how many all zero residuals you got for each. Given just a few short message blocks, it shouldn't take more than a few minutes to find the magic number.

Jon

Reply via email to