web/src/decrypt/ncm.ts

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import {
AudioMimeType,
BytesHasPrefix,
GetArrayBuffer,
GetImageFromURL,
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GetMetaFromFile,
IMusicMeta,
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SniffAudioExt,
WriteMetaToFlac,
WriteMetaToMp3
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} from "@/decrypt/utils";
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import {parseBlob as metaParseBlob} from "music-metadata-browser";
import jimp from 'jimp';
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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";
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import {DecryptResult} from "@/decrypt/entity";
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const CORE_KEY = EncHex.parse("687a4852416d736f356b496e62617857");
const META_KEY = EncHex.parse("2331346C6A6B5F215C5D2630553C2728");
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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;
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const plainText = AES.decrypt(
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// @ts-ignore
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{ciphertext: WordArray.create(cipherText)},
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CORE_KEY,
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{mode: ModeECB, padding: PKCS7}
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);
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;
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WordArray.create()
const plainText = AES.decrypt(
// @ts-ignore
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{
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ciphertext: Base64.parse(
// @ts-ignore
WordArray.create(cipherText.slice(22)).toString(EncUTF8)
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)
},
META_KEY,
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{mode: ModeECB, padding: PKCS7}
).toString(EncUTF8);
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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 (!!this.oriMeta.artist) {
this.oriMeta.artist.forEach(arr => artists.push(<string>arr[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("get 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 {
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if (!this.newMeta || !this.blob) throw Error("bad sequence")
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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),
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blob: this.blob,
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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]
await this._buildMeta()
try {
await this._writeMeta()
} catch (e) {
console.warn("write meta data failed", e)
}
return this.gatherResult()
}
}