Release 260111

opendbc_repo/opendbc/car/secoc.py

@@ -0,0 +1,47 @@
+import struct
+
+from Crypto.Hash import CMAC
+from Crypto.Cipher import AES
+
+def add_mac(key, trip_cnt, reset_cnt, msg_cnt, msg):
+  # TODO: clean up conversion to and from hex
+
+  addr, payload, bus = msg
+  reset_flag = reset_cnt & 0b11
+  msg_cnt_flag = msg_cnt & 0b11
+  payload = payload[:4]
+
+  # Step 1: Build Freshness Value (48 bits)
+  # [Trip Counter (16 bit)][[Reset Counter (20 bit)][Message Counter (8 bit)][Reset Flag (2 bit)][Padding (2 bit)]
+  freshness_value = struct.pack('>HI', trip_cnt, (reset_cnt << 12) | ((msg_cnt & 0xff) << 4) | (reset_flag << 2))
+
+  # Step 2: Build data to authenticate (96 bits)
+  # [Message ID (16 bits)][Payload (32 bits)][Freshness Value (48 bits)]
+  to_auth = struct.pack('>H', addr) + payload + freshness_value
+
+  # Step 3: Calculate CMAC (28 bit)
+  cmac = CMAC.new(key, ciphermod=AES)
+  cmac.update(to_auth)
+  mac = cmac.digest().hex()[:7] # truncated MAC
+
+  # Step 4: Build message
+  # [Payload (32 bit)][Message Counter Flag (2 bit)][Reset Flag (2 bit)][Authenticator (28 bit)]
+  msg_cnt_rst_flag = struct.pack('>B', (msg_cnt_flag << 2) | reset_flag).hex()[1]
+  msg = payload.hex() + msg_cnt_rst_flag + mac
+  payload = bytes.fromhex(msg)
+
+  return (addr, payload, bus)
+
+def build_sync_mac(key, trip_cnt, reset_cnt, id_=0xf):
+  id_ = struct.pack('>H', id_) # 16
+  trip_cnt = struct.pack('>H', trip_cnt) # 16
+  reset_cnt = struct.pack('>I', reset_cnt << 12)[:-1] # 20 + 4 padding
+
+  to_auth = id_ + trip_cnt + reset_cnt # SecOC 11.4.1.1 page 138
+
+  cmac = CMAC.new(key, ciphermod=AES)
+  cmac.update(to_auth)
+
+  msg = "0" + cmac.digest().hex()[:7]
+  msg = bytes.fromhex(msg)
+  return struct.unpack('>I', msg)[0]