canbus: solve IDS-CAN command-auth cipher; add reference implementations

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>
2026-06-12 00:22:09 -04:00
parent 85455e8631
commit 840cfaf5fc
5 changed files with 387 additions and 19 deletions
@@ -0,0 +1,54 @@
+#pragma once
+// IDS-CAN command-auth response cipher for the OneControl write path.
+//
+// 32-round TEA/XTEA-family Feistel, delta 0x9E3779B9, keyed by a per-session
+// 32-bit "Cypher" with the round constants baked in.
+// Verified bit-exact against ids_can_auth.py and 51 captured bus pairs.
+//
+// uint32_t arithmetic wraps mod 2^32 by definition in C++, so no masking needed.
+// ESP32 int is 32-bit (uint32_t == unsigned int): host g++ test is representative.
+
+#include <cstdint>
+#include <cstddef>
+
+namespace ids_can_auth {
+
+// Per-session keys ("Cypher"). REMOTE_CONTROL gates on/off/move.
+enum SessionKey : uint32_t {
+  MANUFACTURING  = 0xB16BA115u,
+  DIAGNOSTIC     = 0xBABECAFEu,
+  REPROGRAMMING  = 0xDEADBEEFu,
+  REMOTE_CONTROL = 0xB16B00B5u,
+  DAQ            = 0x0B00B135u,
+};
+
+// response = Encrypt(challenge). seed = challenge word, cypher = session key.
+inline uint32_t encrypt(uint32_t seed, uint32_t cypher) {
+  uint32_t num = cypher;
+  uint32_t sum = 0x9E3779B9u;  // TEA golden-ratio delta
+  for (int rounds = 32;;) {
+    seed += ((num << 4) + 1131376761u) ^ (num + sum) ^ ((num >> 5) + 1919510376u);
+    if (--rounds <= 0) break;
+    num  += ((seed << 4) + 1948272964u) ^ (seed + sum) ^ ((seed >> 5) + 1400073827u);
+    sum  += 0x9E3779B9u;
+  }
+  return seed;
+}
+
+inline uint32_t remote_control_response(uint32_t challenge) {
+  return encrypt(challenge, REMOTE_CONTROL);
+}
+
+// 4 big-endian challenge bytes (as they arrive in the page-42 payload, after the
+// "00 04" prefix) -> 4 big-endian response bytes (for the page-43 reply).
+inline void remote_control_response_bytes(const uint8_t challenge[4], uint8_t response[4]) {
+  uint32_t c = (uint32_t)challenge[0] << 24 | (uint32_t)challenge[1] << 16 |
+               (uint32_t)challenge[2] << 8  | (uint32_t)challenge[3];
+  uint32_t r = remote_control_response(c);
+  response[0] = (uint8_t)(r >> 24);
+  response[1] = (uint8_t)(r >> 16);
+  response[2] = (uint8_t)(r >> 8);
+  response[3] = (uint8_t)(r);
+}
+
+}  // namespace ids_can_auth