web/src/decrypt/ncm.ts

import {
  AudioMimeType,
  BytesHasPrefix,
  GetArrayBuffer,
  GetImageFromURL,
  GetMetaFromFile,
  IMusicMeta,
  SniffAudioExt,
  WriteMetaToFlac,
  WriteMetaToMp3,
} from '@/decrypt/utils';
import { parseBlob as metaParseBlob } from 'music-metadata-browser';
import jimp from 'jimp';

import AES from 'crypto-js/aes';
import PKCS7 from 'crypto-js/pad-pkcs7';
import ModeECB from 'crypto-js/mode-ecb';
import WordArray from 'crypto-js/lib-typedarrays';
import Base64 from 'crypto-js/enc-base64';
import EncUTF8 from 'crypto-js/enc-utf8';
import EncHex from 'crypto-js/enc-hex';

import { DecryptResult } from '@/decrypt/entity';

const CORE_KEY = EncHex.parse('687a4852416d736f356b496e62617857');
const META_KEY = EncHex.parse('2331346C6A6B5F215C5D2630553C2728');
const MagicHeader = [0x43, 0x54, 0x45, 0x4e, 0x46, 0x44, 0x41, 0x4d];

export async function Decrypt(file: File, raw_filename: string, _: string): Promise<DecryptResult> {
  return new NcmDecrypt(await GetArrayBuffer(file), raw_filename).decrypt();
}

interface NcmMusicMeta {
  //musicId: number
  musicName?: string;
  artist?: Array<string | number>[];
  format?: string;
  album?: string;
  albumPic?: string;
}

interface NcmDjMeta {
  mainMusic: NcmMusicMeta;
}

class NcmDecrypt {
  raw: ArrayBuffer;
  view: DataView;
  offset: number = 0;
  filename: string;
  format: string = '';
  mime: string = '';
  audio?: Uint8Array;
  blob?: Blob;
  oriMeta?: NcmMusicMeta;
  newMeta?: IMusicMeta;
  image?: { mime: string; buffer: ArrayBuffer; url: string };

  constructor(buf: ArrayBuffer, filename: string) {
    const prefix = new Uint8Array(buf, 0, 8);
    if (!BytesHasPrefix(prefix, MagicHeader)) throw Error('此ncm文件已损坏');
    this.offset = 10;
    this.raw = buf;
    this.view = new DataView(buf);
    this.filename = filename;
  }

  _getKeyData(): Uint8Array {
    const keyLen = this.view.getUint32(this.offset, true);
    this.offset += 4;
    const cipherText = new Uint8Array(this.raw, this.offset, keyLen).map((uint8) => uint8 ^ 0x64);
    this.offset += keyLen;

    const plainText = AES.decrypt(
      // @ts-ignore
      { ciphertext: WordArray.create(cipherText) },
      CORE_KEY,
      { mode: ModeECB, padding: PKCS7 },
    );

    const result = new Uint8Array(plainText.sigBytes);

    const words = plainText.words;
    const sigBytes = plainText.sigBytes;
    for (let i = 0; i < sigBytes; i++) {
      result[i] = (words[i >>> 2] >>> (24 - (i % 4) * 8)) & 0xff;
    }

    return result.slice(17);
  }

  _getKeyBox(): Uint8Array {
    const keyData = this._getKeyData();
    const box = new Uint8Array(Array(256).keys());

    const keyDataLen = keyData.length;

    let j = 0;

    for (let i = 0; i < 256; i++) {
      j = (box[i] + j + keyData[i % keyDataLen]) & 0xff;
      [box[i], box[j]] = [box[j], box[i]];
    }

    return box.map((_, i, arr) => {
      i = (i + 1) & 0xff;
      const si = arr[i];
      const sj = arr[(i + si) & 0xff];
      return arr[(si + sj) & 0xff];
    });
  }

  _getMetaData(): NcmMusicMeta {
    const metaDataLen = this.view.getUint32(this.offset, true);
    this.offset += 4;
    if (metaDataLen === 0) return {};

    const cipherText = new Uint8Array(this.raw, this.offset, metaDataLen).map((data) => data ^ 0x63);
    this.offset += metaDataLen;

    WordArray.create();
    const plainText = AES.decrypt(
      // @ts-ignore
      {
        ciphertext: Base64.parse(
          // @ts-ignore
          WordArray.create(cipherText.slice(22)).toString(EncUTF8),
        ),
      },
      META_KEY,
      { mode: ModeECB, padding: PKCS7 },
    ).toString(EncUTF8);

    const labelIndex = plainText.indexOf(':');
    let result: NcmMusicMeta;
    if (plainText.slice(0, labelIndex) === 'dj') {
      const tmp: NcmDjMeta = JSON.parse(plainText.slice(labelIndex + 1));
      result = tmp.mainMusic;
    } else {
      result = JSON.parse(plainText.slice(labelIndex + 1));
    }
    if (result.albumPic) {
      result.albumPic = result.albumPic.replace('http://', 'https://') + '?param=500y500';
    }
    return result;
  }

  _getAudio(keyBox: Uint8Array): Uint8Array {
    this.offset += this.view.getUint32(this.offset + 5, true) + 13;
    const audioData = new Uint8Array(this.raw, this.offset);
    let lenAudioData = audioData.length;
    for (let cur = 0; cur < lenAudioData; ++cur) audioData[cur] ^= keyBox[cur & 0xff];
    return audioData;
  }

  async _buildMeta() {
    if (!this.oriMeta) throw Error('invalid sequence');

    const info = GetMetaFromFile(this.filename, this.oriMeta.musicName);

    // build artists
    let artists: string[] = [];
    if (typeof this.oriMeta.artist === 'string') {
      // v3.0: artist 现在可能是字符串了?
      artists.push(this.oriMeta.artist);
    } else if (Array.isArray(this.oriMeta.artist)) {
      this.oriMeta.artist.forEach((artist) => {
        if (typeof artist === 'string') {
          artists.push(artist);
        } else if (Array.isArray(artist) && artist[0] && typeof artist[0] === 'string') {
          artists.push(artist[0]);
        }
      });
    }

    if (artists.length === 0 && info.artist) {
      artists = info.artist
        .split(',')
        .map((val) => val.trim())
        .filter((val) => val != '');
    }

    if (this.oriMeta.albumPic)
      try {
        this.image = await GetImageFromURL(this.oriMeta.albumPic);
        while (this.image && this.image.buffer.byteLength >= 1 << 24) {
          let img = await jimp.read(Buffer.from(this.image.buffer));
          await img.resize(Math.round(img.getHeight() / 2), jimp.AUTO);
          this.image.buffer = await img.getBufferAsync('image/jpeg');
        }
      } catch (e) {
        console.log('fetch cover image failed', e);
      }

    this.newMeta = { title: info.title, artists, album: this.oriMeta.album, picture: this.image?.buffer };
  }

  async _writeMeta() {
    if (!this.audio || !this.newMeta) throw Error('invalid sequence');

    if (!this.blob) this.blob = new Blob([this.audio], { type: this.mime });
    const ori = await metaParseBlob(this.blob);

    let shouldWrite = !ori.common.album && !ori.common.artists && !ori.common.title;
    if (shouldWrite || this.newMeta.picture) {
      if (this.format === 'mp3') {
        this.audio = WriteMetaToMp3(Buffer.from(this.audio), this.newMeta, ori);
      } else if (this.format === 'flac') {
        this.audio = WriteMetaToFlac(Buffer.from(this.audio), this.newMeta, ori);
      } else {
        console.info(`writing meta for ${this.format} is not being supported for now`);
        return;
      }
      this.blob = new Blob([this.audio], { type: this.mime });
    }
  }

  gatherResult(): DecryptResult {
    if (!this.newMeta || !this.blob) throw Error('bad sequence');
    return {
      title: this.newMeta.title,
      artist: this.newMeta.artists?.join('; '),
      ext: this.format,
      album: this.newMeta.album,
      picture: this.image?.url,
      file: URL.createObjectURL(this.blob),
      blob: this.blob,
      mime: this.mime,
    };
  }

  async decrypt() {
    const keyBox = this._getKeyBox();
    this.oriMeta = this._getMetaData();
    this.audio = this._getAudio(keyBox);
    this.format = this.oriMeta.format || SniffAudioExt(this.audio);
    this.mime = AudioMimeType[this.format];

    try {
      await this._buildMeta();
      await this._writeMeta();
    } catch (e) {
      console.warn('build/write meta failed, skip.', e);
    }

    return this.gatherResult();
  }
}