autel_decrypt.py

import sys

# The a and b values for each index in the block.
keys = {0: (54, 147), 1: (96, 129), 2: (59, 193), 4: (45, 130), 5: (96, 144), 6: (27, 129), 8: (44, 180), 9: (118, 141), 10: (115, 129), 12: (13, 164), 13: (27, 133), 14: (20, 192), 16: (28, 166), 17: (17, 133), 18: (19, 193), 20: (20, 161), 22: (14, 193), 23: (12, 132), 24: (18, 161), 25: (17, 140), 26: (29, 192), 28: (115, 178), 29: (28, 132), 31: (12, 132), 32: (31, 165), 33: (20, 136), 34: (27, 193), 36: (96, 164), 37: (18, 133), 39: (23, 132), 40: (13, 165), 41: (13, 148), 42: (23, 193), 43: (19, 132), 44: (27, 178), 45: (83, 137), 48: (18, 166), 49: (96, 148), 50: (13, 193), 52: (96, 166), 53: (20, 129), 54: (20, 193), 55: (27, 132), 56: (9, 160), 57: (96, 148), 58: (13, 192), 60: (96, 180), 62: (31, 193), 64: (7, 166), 66: (20, 192), 67: (27, 132), 68: (28, 160), 69: (17, 149), 70: (19, 193), 71: (96, 132), 72: (76, 164), 74: (80, 192), 75: (78, 132), 76: (96, 160), 77: (27, 144), 78: (24, 193), 80: (96, 178), 81: (17, 141), 82: (12, 193), 84: (14, 161), 85: (17, 141), 87: (14, 132), 88: (16, 165), 89: (96, 137), 90: (13, 193), 92: (20, 161), 93: (29, 141), 94: (23, 192), 95: (24, 132), 96: (27, 178), 97: (10, 133), 98: (96, 192), 100: (14, 180), 101: (17, 133), 102: (16, 192), 104: (11, 163), 105: (13, 141), 106: (96, 192), 107: (17, 132), 108: (12, 178), 109: (96, 141), 110: (28, 192), 111: (27, 132), 112: (27, 130), 113: (18, 141), 114: (96, 193), 115: (31, 132), 116: (96, 181), 117: (13, 140), 118: (23, 193), 120: (27, 166), 122: (27, 192), 123: (24, 132), 124: (12, 183), 125: (96, 133), 126: (84, 192), 127: (14, 132), 128: (27, 178), 129: (10, 140), 131: (9, 132), 132: (17, 160), 133: (56, 133), 134: (96, 192), 135: (82, 132), 136: (13, 160), 137: (27, 137), 138: (20, 193), 140: (28, 161), 142: (19, 192), 143: (118, 132), 144: (115, 165), 145: (20, 132), 147: (14, 132), 148: (12, 167), 150: (17, 193), 151: (29, 132), 152: (96, 176), 153: (28, 144), 154: (27, 193), 156: (31, 180), 158: (27, 192), 159: (14, 132), 160: (83, 160), 161: (18, 137), 162: (17, 193), 163: (23, 132), 164: (13, 165), 165: (13, 145), 168: (27, 178), 169: (96, 137), 170: (19, 193), 172: (14, 160), 173: (25, 148), 174: (17, 193), 176: (16, 180), 177: (27, 136), 178: (14, 193), 180: (17, 178), 181: (12, 144), 183: (28, 132), 184: (27, 160), 185: (13, 141), 186: (11, 193), 187: (96, 132), 188: (27, 165), 189: (30, 140), 192: (31, 165), 193: (29, 129), 194: (96, 192), 196: (31, 161), 197: (24, 145), 199: (96, 132), 200: (27, 165), 201: (29, 140), 202: (31, 192), 204: (14, 161), 205: (27, 145), 207: (18, 132), 208: (23, 167), 209: (96, 140), 210: (21, 129), 211: (14, 132), 212: (17, 165), 213: (9, 137), 214: (12, 193), 216: (18, 161), 217: (96, 141), 218: (27, 192), 220: (29, 178), 221: (23, 133), 222: (24, 192), 224: (10, 180), 225: (96, 133), 226: (28, 192), 227: (14, 132), 228: (31, 130), 229: (28, 129), 230: (18, 193), 231: (31, 132), 232: (12, 180), 233: (13, 144), 234: (96, 193), 235: (31, 132), 236: (96, 160), 237: (13, 141), 238: (27, 193), 239: (18, 132), 240: (23, 181), 241: (26, 140), 242: (27, 193), 244: (96, 166), 245: (79, 141), 247: (76, 132), 248: (77, 160), 249: (75, 133), 252: (96, 129), 253: (59, 133), 3: (191, 0), 7: (152, 0), 11: (210, 0), 15: (139, 0), 19: (224, 0), 21: (145, 0), 27: (246, 0), 30: (155, 0), 35: (142, 0), 38: (145, 0), 46: (146, 0), 47: (145, 0), 51: (159, 0), 59: (159, 0), 61: (142, 0), 63: (155, 0), 65: (224, 0), 73: (208, 0), 79: (140, 0), 83: (224, 0), 86: (151, 0), 91: (155, 0), 99: (140, 0), 103: (144, 0), 119: (224, 0), 121: (142, 0), 130: (155, 0), 139: (139, 0), 141: (145, 0), 146: (145, 0), 149: (146, 0), 155: (140, 0), 157: (148, 0), 166: (151, 0), 167: (147, 0), 171: (159, 0), 175: (142, 0), 179: (224, 0), 182: (224, 0), 190: (224, 0), 191: (146, 0), 195: (140, 0), 198: (140, 0), 203: (154, 0), 206: (140, 0), 215: (155, 0), 219: (148, 0), 223: (155, 0), 243: (156, 0), 246: (211, 0), 250: (206, 0), 251: (182, 0), 254: (191, 0), 255: (173, 0)}

if len(sys.argv) != 2:
	print("'Decrypts' an obfuscated Autel charger firmware file.")
	print("")
	print(f"Usage: {sys.argv[0]} <filename>")
	print("")
	print("Writes the result to <filename>.decrypted.")
	sys.exit(1)

filename = sys.argv[1]

with open(filename, "rb") as fin:
	with open(f"{filename}.decrypted", "wb") as fout:
		# Skip the header
		fin.read(0x20)

		while True:
			block = fin.read(256)

			if len(block) == 0: break

			for i in range(len(block)):
				(a,b) = keys[i]

				c = ((block[i] + a) ^ b) % 256
				
				fout.write(bytes([c]))

print("Done!")