AES Encryption/Decryption in Node JS similar to Java

Question

I am trying to replicate the Java code for AES Encryption and Decryption in Node JS.

Java Code

    SecretKeySpec skeySpec;
    String key = "a4e1112f45e84f785358bb86ba750f48";

    public void encryptString(String key) throws Exception {
        try {
            skeySpec = new SecretKeySpec(key.getBytes(), "AES");
            cipher = Cipher.getInstance("AES");
            cipher.init(1, skeySpec);
            byte encstr[] = cipher.doFinal(message.getBytes());
            String encData = new String(encstr, "UTF-8");
            System.out.println(encData);
        } catch (NoSuchAlgorithmException nsae) {
            throw new Exception("Invalid Java Version");
        } catch (NoSuchPaddingException nse) {
            throw new Exception("Invalid Key");
        }
    }

Node JS

    var encryptKey = function (text) {
        var cipher = crypto.createCipher('aes256', 'a4e1112f45e84f785358bb86ba750f48');
        var crypted = cipher.update(text,'utf8', 'hex')
        crypted += cipher.final('hex');
        console.log(crypted);
        return crypted;
    }

I am unable to get the exact cipher-text in Node JS, which i am getting in Java.

Answer 1

Your code actually uses different encryption parameters in the 2 cases. AES, being a block cipher, takes: the plain text to encrypt, the initialization vector, also called IV (which is used in conjunction with the plaintext), and the encryption key.

In Java, the IV is, apparently, generated automatically on init() - from the Java SE platform docs for Cipher.init:

The generated parameters can be retrieved using getParameters or getIV (if the parameter is an IV).

In Node.js, if using the deprecated createCipher function, the IV is generated automatically based on the provided key, probably in a different way than in Java, so you will get a different cipher text. However, you should be using the non-deprecated variant crypto.createCipheriv: https://nodejs.org/docs/latest-v12.x/api/crypto.html#crypto_crypto_createcipheriv_algorithm_key_iv_options

In order to exactly reproduce the cipher text, you should:

• Use the same encryption algorithm on both sides - it's best to specify this exactly, for example aes-256-cbc, or an authenticated encryption scheme such as aes-256-gcm, which is harder to use but provides message authentication.
• Use the same IV on both sides, by providing it in the initialization params in Java, and by using createCipheriv in Node; though beware, you should always randomize it in production! See https://stackoverflow.com/a/20888967/6098312

As a closing remark, when using block encryption, you'll usually be generating securely-random IVs, which means the ciphertexts will always differ from one another, even for the same plaintext. This is a good thing! It protects your payload from an attacker who observes the encrypted data and makes conclusions based on message repetitions.