beken bk3231 16-bit CRC add

beken_crc.py

# by mr_woggle - 2024 (c)
# free for all :D
import os

POLY = 0x8005
START_VAL = 0xFFFF

IN_FILE = "test.bin"
OUT_FILE = "test_encrypted.bin"

def crc16(data, poly, init_value=0):
    crc = init_value
    for byte in data:
        crc ^= byte << 8
        for _ in range(8):
            if crc & 0x8000:
                crc = (crc << 1) ^ poly
            else:
                crc <<= 1
    return crc & 0xFFFF

test_message = bytearray(b'\x00' * 3 + b'\x02' + b'\x00' * 28)  # test message, ignore

def add_crc16(input_file, output_file):
    val = START_VAL
    with open(input_file, 'rb') as infile, open(output_file, 'wb') as outfile:
        chunk_size = 32
        while True:
            chunk = infile.read(chunk_size)
            if not chunk:
                break
            if len(chunk) < chunk_size:
                chunk += b'\xFF' * (chunk_size - len(chunk))
                chunk = chunk[:-1] + b'\xFF' # last byte also 0xFF?
            outfile.write(chunk)
            out = crc16(chunk, POLY, val)
            crc_bytes = out.to_bytes(length=2, byteorder='big')
            outfile.write(crc_bytes)  # Add two bytes (16-bit crc)

add_crc16(IN_FILE, OUT_FILE)
print("size after adding crc: ", hex(os.path.getsize(OUT_FILE)))

#crc = crc16(message, POLY, START_VAL)
#print("crc value:", hex(crc))