As GM moves toward Global A and Global B architectures (2016+), they are phasing out simple 5 Byte Seed Keys in favor of:
uint8_t key[5]; uint16_t state = (seed[0] << 8) | seed[1]; uint8_t idx;
for (int i = 0; i < 5; i++) idx = (state >> 8) ^ seed[i]; key[i] = gm_table[idx]; state = (state + key[i]) & 0xFFFF; Gm 5 Byte Seed Key
If you are consistently failing to generate a correct GM 5 Byte Key, check the following:
If you were using a generic tool without the correct algorithm, the tool would fail at Step 3. As GM moves toward Global A and Global
| Seed (hex) | Expected Key (hex) | |----------------------|-----------------------| | 01 02 03 04 05 | A3 8F 4C 2B 71 | | FF FF FF FF FF | 19 2D 5E 8A C3 | | 00 00 00 00 00 | 3A 77 C9 4E 88 | | 12 34 56 78 9A | CD 42 F0 9B 27 |
To clear crash data or reset a deployed SDM (Sensing and Diagnostic Module), the tool must authenticate. This is one of the hardest algorithms to crack, as manufacturers closely guard airbag reset security. : Each ECU vendor may have a unique
: Each ECU vendor may have a unique security table with multiple algorithm rows, making it harder for a single "master key" to exist. Gm 5 Byte Seed Key ((hot))
void gm5_compute_key(const uint8_t seed[5], uint8_t key[5]) seed[1]; for (int i = 0; i < 5; i++) uint8_t idx = (state >> 8) ^ seed[i]; key[i] = gm5_table[idx]; state += key[i];
seed = bytes([0x12, 0x34, 0x56, 0x78, 0x9A]) key = gm5_compute_key(seed) print(f"Seed: seed.hex() -> Key: key.hex()")
The "5 Byte" designation refers to the length of the seed value exchanged during the authentication process. In the spectrum of automotive security: