Find the Algorithm that generates the checksum
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by knivmannen
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Published on 2010-05-24T11:54:42Z
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2010/05/24
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crc
I have a sensing device that transmits a 6-byte message along with an 1-byte counter and supposely a checksum.
The data looks something like this:
------DATA----------- -Counter- --Checksum?--
55 FF 00 00 EC FF ---- 60---------- 1F
The last four bits in the counter are always set 0, i.e those bits are probably not used. The last byte is assumed to be the checksum since it has a quite peculiar nature. It tends to randomly change as data changes.
Now what i need is to find the algorithm to compute this checksum based on --DATA--. what i have tried is all possible CRC-8 polynomials, for each polynomial i have tried to reflect data, toggle it, initiate it with non-zeroes etc etc. Ive come to the conclusion that i am not dealing with a normal crc-algorithm. I have also tried some flether and adler methods without succes, xor stuff back and forth but still i have no clue how to generate the checksum.
My biggest concern is, how is the counter used??? Same data but with different countervalue generates different checksums. I have tried to include the counter in my computations but without any luck.
Here are some other datasamples:
55 FF 00 00 F0 FF A0 38
66 0B EA FF BF FF C0 CA
5E 18 EA FF B7 FF 60 BD
F6 30 16 00 FC FE 10 81
One more thing that might be worth mentioning is that the last byte in the data only takes on the values FF or FE
Plz if u have any tips or tricks that i may try post them here, I am truly desperate.
Thx
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