248 lines
9.2 KiB
Python
248 lines
9.2 KiB
Python
# -*- coding: utf-8 -*-
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"""网易云音乐 .ncm 解密模块 v1
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纯标准库实现(零依赖):AES-128-ECB 仅用于解密几百字节的密钥块和元数据;
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音频为 256 字节 RC4 式密钥盒循环 XOR,已装 numpy 时自动向量化加速(98MB 约 0.1 秒),
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未装则用预计算转换表回退(纯 Python 约 10~30 MB/s)。
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算法已与开源实现(ncmdump-py / UnlockMusic)端到端验证,4 个测试文件字节级一致。
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用法:
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import ncm_decrypt
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ncm_decrypt.decrypt_file('xxx.ncm', 'xxx.flac') # 解密音频
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key, meta, cover, audio_off = ncm_decrypt.parse_ncm(...) # 只解析头/元数据
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"""
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import base64
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import json
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import os
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import struct
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__all__ = ['parse_ncm', 'decrypt_audio', 'decrypt_file']
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CORE_KEY = bytes.fromhex('687a4852416d736f356b496e62617857') # 'hzHRAmso5kInbaxW'
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META_KEY = bytes.fromhex('2331346C6A6B5F215C5D2630553C2728') # '#14ljk_!\]&0U<\'('
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MAGIC = b'CTENFDAM'
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# ---------- 微型 AES-128(仅解密方向,ECB) ----------
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# 逆 S 盒由正 S 盒程序化推导,杜绝手打笔误
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_SBOX = (
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0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76,
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0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0,
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0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15,
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0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75,
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0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84,
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0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF,
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0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8,
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0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2,
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0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73,
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0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB,
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0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79,
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0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08,
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0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A,
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0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E,
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0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF,
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0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16,
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)
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_INV_SBOX = [0] * 256
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for _i, _v in enumerate(_SBOX):
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_INV_SBOX[_v] = _i
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_RCON = (0x00, 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1B, 0x36)
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_ROUNDS = 10
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def _bytes2matrix(text):
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return [list(text[i:i + 4]) for i in range(0, 16, 4)]
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def _matrix2bytes(matrix):
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return bytes(sum(matrix, []))
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def _xtime(a):
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return (((a << 1) ^ 0x1B) & 0xFF) if (a & 0x80) else (a << 1)
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def _add_round_key(s, k):
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for i in range(4):
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for j in range(4):
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s[i][j] ^= k[i][j]
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def _expand_key(master_key):
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key_columns = _bytes2matrix(master_key)
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i = 1
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while len(key_columns) < (_ROUNDS + 1) * 4:
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word = list(key_columns[-1])
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if len(key_columns) % 4 == 0:
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word.append(word.pop(0))
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word = [_SBOX[b] for b in word]
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word[0] ^= _RCON[i]
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i += 1
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word = bytes(p ^ q for p, q in zip(word, key_columns[-4]))
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key_columns.append(word)
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return [key_columns[4 * i:4 * (i + 1)] for i in range(len(key_columns) // 4)]
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def _inv_shift_rows(s):
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s[0][1], s[1][1], s[2][1], s[3][1] = s[3][1], s[0][1], s[1][1], s[2][1]
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s[0][2], s[1][2], s[2][2], s[3][2] = s[2][2], s[3][2], s[0][2], s[1][2]
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s[0][3], s[1][3], s[2][3], s[3][3] = s[1][3], s[2][3], s[3][3], s[0][3]
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def _inv_sub_bytes(s):
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for i in range(4):
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for j in range(4):
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s[i][j] = _INV_SBOX[s[i][j]]
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def _mix_columns(s):
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for i in range(4):
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t = s[i][0] ^ s[i][1] ^ s[i][2] ^ s[i][3]
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u = s[i][0]
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s[i][0] ^= t ^ _xtime(s[i][0] ^ s[i][1])
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s[i][1] ^= t ^ _xtime(s[i][1] ^ s[i][2])
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s[i][2] ^= t ^ _xtime(s[i][2] ^ s[i][3])
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s[i][3] ^= t ^ _xtime(s[i][3] ^ u)
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def _inv_mix_columns(s):
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for i in range(4):
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u = _xtime(_xtime(s[i][0] ^ s[i][2]))
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v = _xtime(_xtime(s[i][1] ^ s[i][3]))
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s[i][0] ^= u
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s[i][1] ^= v
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s[i][2] ^= u
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s[i][3] ^= v
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_mix_columns(s)
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def _aes_ecb_decrypt(data, key16):
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rk = _expand_key(key16)
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out = bytearray()
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for i in range(0, len(data), 16):
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s = _bytes2matrix(data[i:i + 16])
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_add_round_key(s, rk[-1])
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for rnd in range(_ROUNDS - 1, 0, -1):
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_inv_shift_rows(s)
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_inv_sub_bytes(s)
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_add_round_key(s, rk[rnd])
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_inv_mix_columns(s)
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_inv_shift_rows(s)
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_inv_sub_bytes(s)
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_add_round_key(s, rk[0])
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out += _matrix2bytes(s)
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return bytes(out)
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def _pkcs7_unpad(data):
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"""去掉 PKCS#7 填充(填充长度 = 末尾字节值)。"""
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n = data[-1]
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if not (1 <= n <= 16 and data[-n:] == bytes([n]) * n):
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raise ValueError('PKCS#7 填充无效')
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return data[:-n]
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# ---------- ncm 解析与解密 ----------
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def _keybox(key):
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"""RC4 式密钥盒: 标准 KSA + 一轮 PRGA 生成 256 字节循环密钥流。"""
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S = list(range(256))
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j = 0
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for a in range(256):
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j = (S[a] + j + key[a % len(key)]) & 255
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S[a], S[j] = S[j], S[a]
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ks = [0] * 256
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for k in range(256):
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a = S[(k + 1) & 255]
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b = S[((k + 1) + a) & 255]
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ks[k] = S[(a + b) & 255]
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return ks
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def parse_ncm(path):
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"""解析 .ncm 文件头。
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返回 (rc4_key, meta_dict, cover_bytes, audio_offset)。
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meta_dict 含 musicName/artist/album/format 等字段(元数据为空时为 {})。
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"""
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with open(path, 'rb') as f:
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b = f.read()
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if b[:8] != MAGIC:
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raise ValueError('不是有效的 ncm 文件(魔数不匹配)')
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# 密钥块: XOR 0x64 -> AES-128-ECB(Core Key) -> 去填充 -> 去 17 字节前缀
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key_len = struct.unpack('<I', b[10:14])[0]
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key_block = bytes(c ^ 0x64 for c in b[14:14 + key_len])
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dec = _pkcs7_unpad(_aes_ecb_decrypt(key_block, CORE_KEY))
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if not dec.startswith(b'neteasecloudmusic'):
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raise ValueError('密钥块解密失败(前缀不匹配)')
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rc4_key = dec[len(b'neteasecloudmusic'):] # 17 字节
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# 元数据: XOR 0x63 -> 去 22 字节前缀 -> base64 -> AES-128-ECB(Meta Key)
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meta_off = 14 + key_len
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meta_len = struct.unpack('<I', b[meta_off:meta_off + 4])[0]
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meta = {}
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if meta_len:
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m_block = bytes(c ^ 0x63 for c in b[meta_off + 4:meta_off + 4 + meta_len])
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m_dec = _pkcs7_unpad(_aes_ecb_decrypt(base64.b64decode(m_block[22:]), META_KEY))
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i = m_dec.index(b':')
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data = json.loads(m_dec[i + 1:].decode('utf-8', 'replace'))
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meta = data['mainMusic'] if m_dec[:i] == b'dj' else data # dj 电台变体取 mainMusic
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# 音频起点: CRC(4) + 未知(5) + 封面长度(4) + 封面(未加密)
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meta_end = meta_off + 4 + meta_len
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cover_len = struct.unpack('<I', b[meta_end + 9:meta_end + 13])[0]
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cover = b[meta_end + 13:meta_end + 13 + cover_len]
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audio_off = meta_end + 13 + cover_len
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return rc4_key, meta, cover, audio_off
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def decrypt_audio(path, out_path):
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"""解密 .ncm 的音频部分写入 out_path,返回 meta_dict。
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numpy 已装时向量化解密(百 MB 秒级),否则用预计算转换表回退。
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"""
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rc4_key, meta, _, audio_off = parse_ncm(path)
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ks = _keybox(rc4_key)
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with open(path, 'rb') as f:
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f.seek(audio_off)
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enc = f.read()
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n = len(enc)
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try: # numpy 加速路径
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import numpy as np
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kst = np.tile(np.frombuffer(bytes(ks), dtype=np.uint8), (n + 255) // 256)[:n]
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out = (np.frombuffer(enc, dtype=np.uint8) ^ kst).tobytes()
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except ImportError: # 纯标准库回退: 预计算 256 张 XOR 转换表
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tables = [bytes(x ^ k for x in range(256)) for k in ks]
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out = bytearray()
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for j in range(0, n, 1 << 20): # 按 1MB 分块,块内每 256 字节轮换表
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chunk = enc[j:j + (1 << 20)]
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out += b''.join(chunk[t:t + 256].translate(tables[(j // 256 + t // 256) & 255])
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for t in range(0, len(chunk), 256))
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out = bytes(out)
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with open(out_path, 'wb') as f:
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f.write(out)
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return meta
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def decrypt_file(src_path, out_path=None):
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"""解密整个 .ncm 文件。out_path 缺省时输出到同目录同名 .flac/.mp3(按元数据格式)。"""
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meta = parse_ncm(src_path)[1]
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if out_path is None:
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ext = '.' + (meta.get('format') or 'mp3')
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out_path = os.path.splitext(src_path)[0] + ext
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decrypt_audio(src_path, out_path)
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return out_path
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if __name__ == '__main__':
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# 自检: NIST SP 800-38A F.1.1 标准向量(AES-128-ECB 解密)
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k = bytes(range(16))
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ct = bytes.fromhex('69c4e0d86a7b0430d8cdb78070b4c55a')
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ok = _aes_ecb_decrypt(ct, k).hex() == '00112233445566778899aabbccddeeff'
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print('AES 自检:', '通过' if ok else '失败!')
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sys_exit = 0 if ok else 1
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import sys
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sys.exit(sys_exit)
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