e2ee-chat/src/encryption.js

A simple realtime chat SDK for web and mobile apps using socket.io with support for end-to-end encryption and multi-tenant backend integration.

const CryptoJS = require("crypto-js");

function encryptMessage(message, secretKey) {
  try {
    // Match Flutter's encryption approach:
    // 1. Use the secret key directly as Flutter does
    const key = CryptoJS.enc.Utf8.parse(secretKey);

    // 2. Generate SHA-256 hash like Flutter does: sha256.convert(keyBytes.bytes).bytes
    const hashedKey = CryptoJS.SHA256(key);

    // 3. Flutter uses IV.fromLength(16) - this creates a zero IV in the package
    // Based on Flutter's encrypt package behavior with same IV
    const iv = CryptoJS.lib.WordArray.create([0, 0, 0, 0]); // 16 bytes of zeros

    // 4. Encrypt using AES-256-CBC
    const encrypted = CryptoJS.AES.encrypt(message, hashedKey, {
      iv: iv,
      mode: CryptoJS.mode.CBC,
      padding: CryptoJS.pad.Pkcs7,
    });

    // 5. Return base64 encoded string (matching Flutter's .base64 output)
    return encrypted.toString();
  } catch (e) {
    console.error("Error encrypting message:", e);
    throw e;
  }
}

function decryptMessage(encryptedText, secretKey) {
  try {
    // Match Flutter's decryption approach:
    // 1. Use the secret key directly as Flutter does
    const key = CryptoJS.enc.Utf8.parse(secretKey);

    // 2. Generate SHA-256 hash like Flutter does
    const hashedKey = CryptoJS.SHA256(key);

    // 3. Use the same IV as encryption
    const iv = CryptoJS.lib.WordArray.create([0, 0, 0, 0]); // 16 bytes of zeros

    // 4. Decrypt the base64 encrypted text
    const decrypted = CryptoJS.AES.decrypt(encryptedText, hashedKey, {
      iv: iv,
      mode: CryptoJS.mode.CBC,
      padding: CryptoJS.pad.Pkcs7,
    });

    // 5. Convert back to UTF-8 string
    const decryptedText = decrypted.toString(CryptoJS.enc.Utf8);

    if (!decryptedText) {
      throw new Error("Failed to decrypt message - invalid result");
    }

    return decryptedText;
  } catch (e) {
    console.error("Error decrypting message:", e);
    console.error("Encrypted text was:", encryptedText);
    console.error("Secret key was:", secretKey);

    // Let's try alternative approaches for debugging
    try {
      // Try the old simple method as fallback
      const bytes = CryptoJS.AES.decrypt(encryptedText, secretKey);
      const result = bytes.toString(CryptoJS.enc.Utf8);
      if (result) {
        console.log("Fallback decryption worked");
        return result;
      }
    } catch (fallbackError) {
      console.error("Fallback decryption also failed:", fallbackError);
    }

    throw e;
  }
}

module.exports = {
  encryptMessage,
  decryptMessage,
};