a function to decrypt WA Media

wa-decrypt.js

/**
 * this code is copied from https://github.com/open-wa/wa-decrypt-nodejs
 * i just made it more simplified
 */

const { default: axios } = require('axios');
const crypto = require('crypto');
const hkdf = require('futoin-hkdf');
const atob = require('atob');

const fixPadding = (data, expectedSize) => {
    const padding = (16 - (expectedSize % 16)) & 0xf;
    if (padding > 0) {
        if ((expectedSize + padding) == data.length) {
            //  console.log(`trimmed: ${padding} bytes`);
            data = data.slice(0, data.length - padding);
        } else if ((data.length + padding) == expectedSize) {
            // console.log(`adding: ${padding} bytes`);
            const arr = new Uint16Array(padding).map(() => padding);
            data = Buffer.concat([data, Buffer.from(arr)]);
        }
    }
    // @ts-ignore
    return Buffer.from(data, 'utf-8');
};

const hexToBytes = (hexStr) => {
    const intArray = [];
    for (let i = 0; i < hexStr.length; i += 2) {
        intArray.push(parseInt(hexStr.substr(i, 2), 16));
    }
    return new Uint8Array(intArray);
};

const base64ToBytes = (base64Str) => {
    const binaryStr = atob(base64Str);
    const byteArray = new Uint8Array(binaryStr.length);
    for (let i = 0; i < binaryStr.length; i++) {
        byteArray[i] = binaryStr.charCodeAt(i);
    }
    return byteArray;
};

const mediaTypes = {
    IMAGE: 'Image',
    VIDEO: 'Video',
    AUDIO: 'Audio',
    PTT: 'Audio',
    DOCUMENT: 'Document',
    STICKER: 'Image',
};

const magix = (fileData, mediaKeyBase64, mediaType, expectedSize = '', mimetype = '') => {
    const encodedHex = fileData.toString('hex');
    const encodedBytes = hexToBytes(encodedHex);
    const mediaKeyBytes = base64ToBytes(mediaKeyBase64);
    const info = `WhatsApp ${mediaTypes[mediaType.toUpperCase()] || mediaTypes[Object.keys(mediaTypes).filter((type) => mimetype.includes(type.toLowerCase()))[0]]} Keys`;
    const hash = 'sha256';
    const salt = new Uint8Array(32);
    const expandedSize = 112;
    const mediaKeyExpanded = hkdf(mediaKeyBytes, expandedSize, {
        salt,
        info,
        hash,
    });
    const iv = mediaKeyExpanded.slice(0, 16);
    const cipherKey = mediaKeyExpanded.slice(16, 48);
    const decipher = crypto.createDecipheriv('aes-256-cbc', cipherKey, iv);
    const decoded = decipher.update(encodedBytes);
    const mediaDataBuffer = expectedSize ? fixPadding(decoded, expectedSize) : decoded;
    return mediaDataBuffer;
};
const decryptMedia = async (message) => {
    const options = {
        responseType: 'arraybuffer',
        headers: {
            'User-Agent': 'WhatsApp/2.16.352 Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.92 Safari/537.36',
            DNT: 1,
            'Upgrade-Insecure-Requests': 1,
            origin: 'https://web.whatsapp.com/',
            referer: 'https://web.whatsapp.com/',
        },
    };

    const res = await axios.get(message.deprecatedMms3Url.trim(), options);

    const buff = Buffer.from(res.data, 'binary');
    return magix(buff, message.mediaKey, message.type, message.size, message.mimetype);
};

const message = {
    type: 'image',
    deprecatedMms3Url: 'https://mmg.whatsapp.net/v/t62.7118-24/32988171_775415480878877_6103136834163776922_n.enc?ccb=11-4&oh=01_AdS7iKRPVP9je_HosEutBTpM5s7jFPlWIK3WVz19bZM4xA&oe=647B3771&mms3=true',
    directPath: '/v/t62.7118-24/32988171_775415480878877_6103136834163776922_n.enc?ccb=11-4&oh=01_AdS7iKRPVP9je_HosEutBTpM5s7jFPlWIK3WVz19bZM4xA&oe=647B3771',
    staticUrl: '',
    mimetype: 'image/jpeg',
    caption: 'Kek punya @areta',
    filehash: 'c4ovTdfcoO5LClgIPRJTnwzA+eUdGYIx670iLLlKiNU=',
    encFilehash: '1jyLb2XbsTnca0CZZ+Du7Rux0xPeW75IJ80ChxUZDdA=',
    size: 189236,
    height: 1520,
    width: 720,
    mediaKey: 'b+Jq/CPv8E1PJy+S0FB9TD4gQGVpcoVFeSKzBqPUYZI=',
    mediaKeyTimestamp: 1683209371,
    body: '',
    interactiveAnnotations: [],
    scanLengths: [
        11842,
        65657,
        46750,
        64987,
    ],
    scansSidecar: {},
    isViewOnce: true,
};

const fs = require('fs');

decryptMedia(message).then((res) => fs.writeFileSync('img.jpeg', res));