Reconstruct

src/decrypt/ncm.js

@@ -0,0 +1,171 @@
+const CryptoJS = require("crypto-js");
+const ID3Writer = require("browser-id3-writer");
+const util = require("./util");
+const CORE_KEY = CryptoJS.enc.Hex.parse("687a4852416d736f356b496e62617857");
+const META_KEY = CryptoJS.enc.Hex.parse("2331346C6A6B5F215C5D2630553C2728");
+
+
+export {Decrypt};
+
+async function Decrypt(file) {
+
+    const fileBuffer = await util.GetArrayBuffer(file);
+    const dataView = new DataView(fileBuffer);
+
+    if (dataView.getUint32(0, true) !== 0x4e455443 ||
+        dataView.getUint32(4, true) !== 0x4d414446)
+        return {status: false, message: "此ncm文件已损坏"};
+
+
+    const keyDataObj = getKeyData(dataView, fileBuffer, 10);
+    const keyBox = getKeyBox(keyDataObj.data);
+
+    const musicMetaObj = getMetaData(dataView, fileBuffer, keyDataObj.offset);
+    const musicMeta = musicMetaObj.data;
+
+    let audioOffset = musicMetaObj.offset + dataView.getUint32(musicMetaObj.offset + 5, true) + 13;
+    let audioData = new Uint8Array(fileBuffer, audioOffset);
+
+    for (let cur = 0; cur < audioData.length; ++cur) {
+        audioData[cur] ^= keyBox[cur & 0xff];
+    }
+
+    if (musicMeta.format === undefined) {
+        const [f, L, a, C] = audioData;
+        if (f === 0x66 && L === 0x4c && a === 0x61 && C === 0x43) {
+            musicMeta.format = "flac";
+        } else {
+            musicMeta.format = "mp3";
+        }
+    }
+    const mime = util.AudioMimeType[musicMeta.format];
+
+    const artists = [];
+    musicMeta.artist.forEach(arr => {
+        artists.push(arr[0]);
+    });
+    if (musicMeta.format === "mp3") {
+        audioData = await writeID3(audioData, artists, musicMeta.musicName, musicMeta.album, musicMeta.albumPic)
+    }
+
+    const musicData = new Blob([audioData], {type: mime});
+    const musicUrl = URL.createObjectURL(musicData);
+    const filename = artists.join(" & ") + " - " + musicMeta.musicName + "." + musicMeta.format;
+    return {
+        status: true,
+        filename: filename,
+        title: musicMeta.musicName,
+        artist: artists.join(" & "),
+        album: musicMeta.album,
+        picture: musicMeta.albumPic,
+        file: musicUrl,
+        mime: mime
+    };
+}
+
+async function writeID3(audioData, artistList, title, album, picture) {
+    const writer = new ID3Writer(audioData);
+    writer.setFrame("TPE1", artistList)
+        .setFrame("TIT2", title)
+        .setFrame("TALB", album);
+    if (picture !== "") {
+        try {
+            const img = await (await fetch(picture)).arrayBuffer();
+            writer.setFrame('APIC', {
+                type: 3,
+                data: img,
+                description: 'Cover'
+            })
+        } catch (e) {
+            console.log("Fail to write cover image!");
+        }
+    }
+    writer.addTag();
+    return writer.arrayBuffer;
+}
+
+function getKeyData(dataView, fileBuffer, offset) {
+    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 {offset: offset, data: result.slice(17)};
+}
+
+function getKeyBox(keyData) {
+    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
+ */
+
+function getMetaData(dataView, fileBuffer, offset) {
+    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 {data: result, offset: offset};
+}
+
+