I'm working on an RFID reader that has partial implementation with ISO/IEC 14443-4 although not specifically compliant. I can decode a lot of the strings and understand the command base but I have not been able to crack the check sum.
Read commands are 4 bytes in the format
0x82 Read Chunk 0xYY Chunk Number 2 Byte checksum
the response is to echo the Read command, chunk Id, 32 Bytes of data then 2 byte checksum.
I've tried the hex strings with a bunch of standard checksum calculators as well as looking for things like logical ands but cannot find any rule for how they are generated. Is there some other techniques for this style of checksum?
8208942d 82081101004049424d2020202020363831303232393437310004000d1f0e000d220a273b 82091d3c 8209000d2591000e8521000e8521000e881d363955320000000000000000386c1940c1a4 821b8e0f 821b00000000000000000000000000000000000000000000000000000000000000008ca8 821c317b 821c0000000000000000000000000000000000000000000000000000000000000000b461 821db86a 821d0000000000000000000000000000000000000000000000000000000000000000d721