web/src/plugins/ncm.js

const CryptoJS = require("crypto-js");
const CORE_KEY = CryptoJS.enc.Hex.parse("687a4852416d736f356b496e62617857");
const META_KEY = CryptoJS.enc.Hex.parse("2331346C6A6B5F215C5D2630553C2728");

const audio_mime_type = {
    mp3: "audio/mpeg",
    flac: "audio/flac"
};


export {Decrypt};

async function Decrypt(file) {

    const fileBuffer = await new Promise(reslove => {
        const reader = new FileReader();
        reader.onload = (e) => {
            reslove(e.target.result);
        };
        reader.readAsArrayBuffer(file);
    });

    const dataView = new DataView(fileBuffer);

    if (dataView.getUint32(0, true) !== 0x4e455443 ||
        dataView.getUint32(4, true) !== 0x4d414446
    ) {
        console.log({type: "error", data: "not ncm file"});
        return;
    }

    let offset = 10;

    const keyData = (() => {
        const keyLen = dataView.getUint32(offset, true);
        offset += 4;
        const cipherText = new Uint8Array(fileBuffer, offset, keyLen).map(
            uint8 => uint8 ^ 0x64
        );
        offset += keyLen;

        const plainText = CryptoJS.AES.decrypt(
            {ciphertext: CryptoJS.lib.WordArray.create(cipherText)},
            CORE_KEY,
            {
                mode: CryptoJS.mode.ECB,
                padding: CryptoJS.pad.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);
    })();

    const keyBox = (() => {
        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];
        });
    })();

    /**
     * @typedef {Object} MusicMetaType
     * @property {Number} musicId
     * @property {String} musicName
     * @property {[[String, Number]]} artist
     * @property {String} album
     * @property {"flac"|"mp3"} format
     * @property {String} albumPic
     */

    /** @type {MusicMetaType|undefined} */
    const musicMeta = (() => {
        const metaDataLen = dataView.getUint32(offset, true);
        offset += 4;
        if (metaDataLen === 0) {
            return {};
        }

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

        const plainText = CryptoJS.AES.decrypt(
            {
                ciphertext: CryptoJS.enc.Base64.parse(
                    CryptoJS.lib.WordArray.create(cipherText.slice(22)).toString(CryptoJS.enc.Utf8)
                )
            },
            META_KEY,
            {mode: CryptoJS.mode.ECB, padding: CryptoJS.pad.Pkcs7}
        );

        const result = JSON.parse(plainText.toString(CryptoJS.enc.Utf8).slice(6));
        result.albumPic = result.albumPic.replace("http:", "https:");
        return result;
    })();

    offset += dataView.getUint32(offset + 5, true) + 13;

    const audioData = new Uint8Array(fileBuffer, offset);
    const audioDataLen = audioData.length;


    for (let cur = 0; cur < audioDataLen; ++cur) {
        audioData[cur] ^= keyBox[cur & 0xff];
    }


    if (musicMeta.format === undefined) {
        musicMeta.format = (() => {
            const [f, L, a, C] = audioData;
            if (f === 0x66 && L === 0x4c && a === 0x61 && C === 0x43) {
                return "flac";
            }
            return "mp3";
        })();
    }
    const mime = audio_mime_type[musicMeta.format];
    const musicData = new Blob([audioData], {
        type: mime
    });

    const musicUrl = URL.createObjectURL(musicData);

    const artists = [];
    musicMeta.artist.forEach(arr => {
        artists.push(arr[0]);
    });
    const filename = artists.join(" & ") + " - " + musicMeta.musicName + "." + musicMeta.format;
    return {
        meta: musicMeta,
        file: musicUrl,
        picture: musicMeta.albumPic,
        title: musicMeta.musicName,
        album: musicMeta.album,
        artist: artists.join(" & "),
        filename: filename,
        mime: mime
    };
}