wesandClaude Fable 5
840cfaf5fc
The CAN write gate (page-42/43 challenge/response) is a 32-round TEA/XTEA-family Feistel keyed by a per-session 32-bit key; REMOTE_CONTROL = 0xB16B00B5. Verified 51/51 against captured challenge/response pairs across nodes 2A/61/75/F8 (one global key, not per-node), so the CAN path can now actuate, not just sense. - ids_can_auth.py Python reference + self-test (51/51) - esphome/ids_can_auth.h C++ port for the ESP32 node (host-tested 8/8) - sniff/analyze_auth.py structural analysis (rules out affine; confirms keyed cipher) - sniff/auth-pairs-multinode-2026-06-11.txt +9 pairs across 4 nodes - README document the cipher, session keys, unlock sequence Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
55 lines
2.0 KiB
C++
55 lines
2.0 KiB
C++
#pragma once
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// IDS-CAN command-auth response cipher for the OneControl write path.
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//
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// 32-round TEA/XTEA-family Feistel, delta 0x9E3779B9, keyed by a per-session
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// 32-bit "Cypher" with the round constants baked in.
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// Verified bit-exact against ids_can_auth.py and 51 captured bus pairs.
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//
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// uint32_t arithmetic wraps mod 2^32 by definition in C++, so no masking needed.
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// ESP32 int is 32-bit (uint32_t == unsigned int): host g++ test is representative.
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#include <cstdint>
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#include <cstddef>
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namespace ids_can_auth {
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// Per-session keys ("Cypher"). REMOTE_CONTROL gates on/off/move.
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enum SessionKey : uint32_t {
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MANUFACTURING = 0xB16BA115u,
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DIAGNOSTIC = 0xBABECAFEu,
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REPROGRAMMING = 0xDEADBEEFu,
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REMOTE_CONTROL = 0xB16B00B5u,
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DAQ = 0x0B00B135u,
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};
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// response = Encrypt(challenge). seed = challenge word, cypher = session key.
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inline uint32_t encrypt(uint32_t seed, uint32_t cypher) {
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uint32_t num = cypher;
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uint32_t sum = 0x9E3779B9u; // TEA golden-ratio delta
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for (int rounds = 32;;) {
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seed += ((num << 4) + 1131376761u) ^ (num + sum) ^ ((num >> 5) + 1919510376u);
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if (--rounds <= 0) break;
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num += ((seed << 4) + 1948272964u) ^ (seed + sum) ^ ((seed >> 5) + 1400073827u);
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sum += 0x9E3779B9u;
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}
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return seed;
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}
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inline uint32_t remote_control_response(uint32_t challenge) {
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return encrypt(challenge, REMOTE_CONTROL);
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}
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// 4 big-endian challenge bytes (as they arrive in the page-42 payload, after the
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// "00 04" prefix) -> 4 big-endian response bytes (for the page-43 reply).
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inline void remote_control_response_bytes(const uint8_t challenge[4], uint8_t response[4]) {
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uint32_t c = (uint32_t)challenge[0] << 24 | (uint32_t)challenge[1] << 16 |
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(uint32_t)challenge[2] << 8 | (uint32_t)challenge[3];
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uint32_t r = remote_control_response(c);
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response[0] = (uint8_t)(r >> 24);
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response[1] = (uint8_t)(r >> 16);
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response[2] = (uint8_t)(r >> 8);
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response[3] = (uint8_t)(r);
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}
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} // namespace ids_can_auth
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