ncmdump.py

import binascii
import struct
import base64
import json
import os
import sys
import datetime
from Crypto.Cipher import AES

def getNowtime():
    return datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S')

class logger:
    def info(msg):
        print(getNowtime() + " [Info] " + msg)
    def error(msg):
        print(getNowtime() + " [Error] " + msg)
    def warning(msg):
        print(getNowtime() + " [Warning] " + msg)
    def debug(msg):
        if "--debug" in sys.argv:
            print(getNowtime() + " [Debug] " + msg)

def dump(file_path, remove):
    # hex to str
    core_key = binascii.a2b_hex("687A4852416D736F356B496E62617857")
    meta_key = binascii.a2b_hex("2331346C6A6B5F215C5D2630553C2728")
    unpad = lambda s: s[0:-(s[-1] if type(s[-1]) is int else ord(s[-1]))]
    f = open(file_path, 'rb')
    header = f.read(8)
    # str to hex
    assert binascii.b2a_hex(header) == b'4354454e4644414d'
    f.seek(2, 1)
    key_length = f.read(4)
    key_length = struct.unpack('<I', bytes(key_length))[0]
    key_data = f.read(key_length)
    key_data_array = bytearray(key_data)
    for i in range(0, len(key_data_array)):
        key_data_array[i] ^= 0x64
    key_data = bytes(key_data_array)
    cryptor = AES.new(core_key, AES.MODE_ECB)
    key_data = unpad(cryptor.decrypt(key_data))[17:]
    key_length = len(key_data)
    key_data = bytearray(key_data)
    key_box = bytearray(range(256))
    c = 0
    last_byte = 0
    key_offset = 0
    for i in range(256):
        swap = key_box[i]
        c = (swap + last_byte + key_data[key_offset]) & 0xff
        key_offset += 1
        if key_offset >= key_length:
            key_offset = 0
        key_box[i] = key_box[c]
        key_box[c] = swap
        last_byte = c
    meta_length = f.read(4)
    meta_length = struct.unpack('<I', bytes(meta_length))[0]
    meta_data = f.read(meta_length)
    meta_data_array = bytearray(meta_data)
    for i in range(0, len(meta_data_array)):
        meta_data_array[i] ^= 0x63
    meta_data = bytes(meta_data_array)
    meta_data = base64.b64decode(meta_data[22:])
    cryptor = AES.new(meta_key, AES.MODE_ECB)
    meta_data = unpad(cryptor.decrypt(meta_data)).decode('utf-8')[6:]
    meta_data = json.loads(meta_data)
    crc32 = f.read(4)
    crc32 = struct.unpack('<I', bytes(crc32))[0]
    f.seek(5, 1)
    image_size = f.read(4)
    image_size = struct.unpack('<I', bytes(image_size))[0]
    image_data = f.read(image_size)
    file_name = f.name.split("/")[-1].split(".ncm")[0] + '.' + meta_data['format']
    m = open(os.path.join(os.path.split(file_path)[0], file_name), 'wb')
    chunk = bytearray()
    while True:
        chunk = bytearray(f.read(0x8000))
        chunk_length = len(chunk)
        if not chunk:
            break
        for i in range(1, chunk_length + 1):
            j = i & 0xff
            chunk[i - 1] ^= key_box[(key_box[j] + key_box[(key_box[j] + j) & 0xff]) & 0xff]
        m.write(chunk)
    m.close()
    f.close()
    if remove:
        os.remove(file_path)
    return file_name


if __name__ == "__main__":
    args = sys.argv[1:]
    __list__ = []
    remove = False
    if "--remove-source" in args:
        remove = True
    if "--all" in args:
        files = os.listdir(os.getcwd())
        for file in files:
            if file.endswith(".ncm"):
                __list__.append(file)
    if "--no-output" in args:
        for file in __list__:
            dump(file, remove)
    else:
        for file in __list__:
            logger.info("正在转换 (" + str(__list__.index(file) + 1) + "/" + str(len(__list__)) + "): " + file)
            logger.info("转换成功! 输出文件名为 " + dump(file, remove))
        logger.info("转换完成! 共转换 " + str(len(__list__)) + " 个文件")