GM relied on the algorithm being secret. However, once the firmware is extracted, the algorithm is exposed.
temp[i] = Seed[i] ^ table[Seed[(i+1)%5]] Key[i] = (temp[i] * 0x23 + 0x17) & 0xFF gm 5 byte seed key
Before focusing on GM’s specific implementation, we must understand the concept of a Seed Key (S/K) system. It is a challenge-response authentication protocol used on the Controller Area Network (CAN) bus or K-Line (ISO 9141-2). GM relied on the algorithm being secret
Failure to compute the correct key results in a $35 (invalid key) response and a security delay timer. It is a challenge-response authentication protocol used on
: Modern vehicles, including those made by General Motors, use sophisticated security systems to prevent unauthorized access and theft. Part of these systems can involve cryptographic keys or seed keys that are used to authenticate and authorize access to the vehicle's systems.
Both the ECU and the tool run this Seed through a proprietary, secret mathematical function (the algorithm) using a specific access key or "mask" stored in the firmware. The Key Response: The tool sends its calculated 5-byte "Key" back to the ECU. Validation:
The 5-byte era will remain relevant for GM vehicles roughly 2010–2020.