NeteaseMusicLyricDownloader/modules/utils/dump.py

import binascii
import json
import os
import struct
import base64

from Cryptodome.Cipher import AES
from Cryptodome.Util.Padding import unpad
from Cryptodome.Util.strxor import strxor as xor
from mutagen import mp3, flac, id3


def load_and_decrypt_from_ncm(file_path, target_dir, out_format) -> dict | str:  # author: Nzix Repo: nondanee

    core_key = binascii.a2b_hex('687A4852416D736F356B496E62617857')
    meta_key = binascii.a2b_hex('2331346C6A6B5F215C5D2630553C2728')

    f = open(file_path, 'rb')

    # magic header
    header = f.read(8)
    assert binascii.b2a_hex(header) == b'4354454e4644414d'

    f.seek(2, 1)

    # key data
    key_length = f.read(4)
    key_length = struct.unpack('<I', bytes(key_length))[0]

    key_data = bytearray(f.read(key_length))
    key_data = bytes(bytearray([byte ^ 0x64 for byte in key_data]))

    cryptor = AES.new(core_key, AES.MODE_ECB)
    key_data = unpad(cryptor.decrypt(key_data), 16)[17:]
    key_length = len(key_data)

    # S-box (standard RC4 Key-scheduling algorithm)
    key = bytearray(key_data)
    S = bytearray(range(256))
    j = 0

    for i in range(256):
        j = (j + S[i] + key[i % key_length]) & 0xFF
        S[i], S[j] = S[j], S[i]

    # meta data
    meta_length = f.read(4)
    meta_length = struct.unpack('<I', bytes(meta_length))[0]

    if meta_length:
        meta_data = bytearray(f.read(meta_length))
        meta_data = bytes(bytearray([byte ^ 0x63 for byte in meta_data]))
        identifier = meta_data.decode('utf-8')
        meta_data = base64.b64decode(meta_data[22:])

        cryptor = AES.new(meta_key, AES.MODE_ECB)
        meta_data = unpad(cryptor.decrypt(meta_data), 16).decode('utf-8')
        meta_data = json.loads(meta_data[6:])
    else:
        meta_data = {'format': 'flac' if os.fstat(f.fileno()).st_size > 1024 ** 2 * 16 else 'mp3'}

    f.seek(5, 1)

    # album cover
    image_space = f.read(4)
    image_space = struct.unpack('<I', bytes(image_space))[0]
    image_size = f.read(4)
    image_size = struct.unpack('<I', bytes(image_size))[0]
    image_data = f.read(image_size) if image_size else None

    f.seek(image_space - image_size, 1)

    # media data
    if meta_length:
        output_path = os.path.join(target_dir, out_format % {"name": meta_data["musicName"], "artists": "".join(
            [x[0]+"," for x in meta_data["artist"]]
        )[:-1]} + "." + meta_data["format"])
    else:
        output_path = os.path.join(target_dir, "Unnamed." + meta_data["format"])

    data = f.read()
    f.close()

    # stream cipher (modified RC4 Pseudo-random generation algorithm)
    stream = [S[(S[i] + S[(i + S[i]) & 0xFF]) & 0xFF] for i in range(256)]
    stream = bytes(bytearray(stream * (len(data) // 256 + 1))[1:1 + len(data)])
    data = xor(data, stream)

    m = open(output_path, 'wb')
    m.write(data)
    m.close()

    # media tag
    if meta_length:
        def embed(item, content, t):
            item.encoding = 0
            item.type = t
            item.mime = 'image/png' if content[0:4] == binascii.a2b_hex('89504E47') else 'image/jpeg'
            item.data = content

        if image_data:
            if meta_data['format'] == 'flac':
                audio = flac.FLAC(output_path)
                image = flac.Picture()
                embed(image, image_data, 3)
                audio.clear_pictures()
                audio.add_picture(image)
                audio.save()
            elif meta_data['format'] == 'mp3':
                audio = mp3.MP3(output_path)
                image = id3.APIC()
                embed(image, image_data, 6)
                audio.tags.add(image)
                audio.save()

        if meta_length:
            if meta_data['format'] == 'flac':
                audio = flac.FLAC(output_path)
                audio['description'] = identifier
            else:
                audio = mp3.EasyMP3(output_path)
                audio['title'] = 'placeholder'
                audio.tags.RegisterTextKey('comment', 'COMM')
                audio['comment'] = identifier
            audio['title'] = meta_data['musicName']
            audio['album'] = meta_data['album']
            audio['artist'] = '/'.join([artist[0] for artist in meta_data['artist']])
            audio.save()
        return meta_data
    else:
        return "no_meta_data"