MarlinFirmware/buildroot/share/PlatformIO/scripts/chitu_crypt.py

#
# 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);