The GM 5-Bit Seed/Key algorithm serves as a basic "keep out" mechanism for unauthorized diagnostic access but provides no meaningful security against a determined attacker. It is a proprietary implementation of a simple symmetric cipher that can be defeated through static analysis or brute-force deduction.
However, the most widespread algorithm is an combined with bitwise XOR, sometimes called the "GM 5-byte rolling seed-key" or "GM Crypto 1". gm 5 byte seed key
The ECU generates a random 5-byte hexadecimal number (the "Seed") and sends it back to the tool. The GM 5-Bit Seed/Key algorithm serves as a
Simple Python code that calculates GM 5 byte keys ... - GitHub gm 5 byte seed key
