# # chitu_crypt.py # Customizations for Chitu boards # import pioutil if pioutil.is_pio_build(): import struct,uuid,marlin board = marlin.env.BoardConfig() def calculate_crc(contents, seed): accumulating_xor_value = seed; for i in range(0, len(contents), 4): value = struct.unpack('<I', contents[ i : i + 4])[0] accumulating_xor_value = accumulating_xor_value ^ value return accumulating_xor_value def xor_block(r0, r1, block_number, block_size, file_key): # This is the loop counter loop_counter = 0x0 # This is the key length key_length = 0x18 # This is an initial seed xor_seed = 0x4BAD # This is the block counter block_number = xor_seed * block_number #load the xor key from the file r7 = file_key for loop_counter in range(0, block_size): # meant to make sure different bits of the key are used. xor_seed = int(loop_counter / key_length) # IP is a scratch register / R12 ip = loop_counter - (key_length * xor_seed) # xor_seed = (loop_counter * loop_counter) + block_number xor_seed = (loop_counter * loop_counter) + block_number # shift the xor_seed left by the bits in IP. xor_seed = xor_seed >> ip # load a byte into IP ip = r0[loop_counter] # XOR the seed with r7 xor_seed = xor_seed ^ r7 # and then with IP xor_seed = xor_seed ^ ip #Now store the byte back r1[loop_counter] = xor_seed & 0xFF #increment the loop_counter loop_counter = loop_counter + 1 def encrypt_file(input, output_file, file_length): input_file = bytearray(input.read()) block_size = 0x800 key_length = 0x18 uid_value = uuid.uuid4() file_key = int(uid_value.hex[0:8], 16) xor_crc = 0xEF3D4323; # the input file is exepcted to be in chunks of 0x800 # so round the size while len(input_file) % block_size != 0: input_file.extend(b'0x0') # write the file header output_file.write(struct.pack(">I", 0x443D2D3F)) # encrypt the contents using a known file header key # write the file_key output_file.write(struct.pack("<I", file_key)) #TODO - how to enforce that the firmware aligns to block boundaries? block_count = int(len(input_file) / block_size) print ("Block Count is ", block_count) for block_number in range(0, block_count): block_offset = (block_number * block_size) block_end = block_offset + block_size block_array = bytearray(input_file[block_offset: block_end]) xor_block(block_array, block_array, block_number, block_size, file_key) for n in range (0, block_size): input_file[block_offset + n] = block_array[n] # update the expected CRC value. xor_crc = calculate_crc(block_array, xor_crc) # write CRC output_file.write(struct.pack("<I", xor_crc)) # finally, append the encrypted results. output_file.write(input_file) return # Encrypt ${PROGNAME}.bin and save it as 'update.cbd' def encrypt(source, target, env): from pathlib import Path fwpath = Path(target[0].path) fwsize = fwpath.stat().st_size enname = board.get("build.crypt_chitu") enpath = Path(target[0].dir.path) fwfile = fwpath.open("rb") enfile = (enpath / enname).open("wb") print(f"Encrypting {fwpath} to {enname}") encrypt_file(fwfile, enfile, fwsize) fwfile.close() enfile.close() fwpath.unlink() marlin.relocate_firmware("0x08008800") marlin.add_post_action(encrypt);