CryptoJs decrypt function equivalent in Java

Question

I'm trying to decrypt a token that the server I'm using brings in order to load correctly users access to the page.

I already achieved the goal using CryptoJs using JavaScript. However now I need to transfer that function to my java backend.

Look my code using CryptoJs which works correctly

const token = "U2FsdGVkX1+6YueVRKp6h0dZfk/a8AC9vyFfAjxD4nb7mXsKrM7rI7xZ0OgrF1sShHYNLMJglz4+67n/I7P+fg=="
const key = "p80a0811-47db-2c39-bcdd-4t3g5h2d5d1a"

// Decrypt
const iv = CryptoJS.enc.Utf8.parse(key);
const decryptedToken = CryptoJS.AES.decrypt(token, key, {
  keySize: 16,
  iv,
  mode: CryptoJS.mode.CBC,
  padding: CryptoJS.pad.Pkcs7,
});

const stringToken = decryptedToken.toString(CryptoJS.enc.Utf8);
const dataToUse = JSON.parse(stringToken)

console.log("decryptedToken => ", stringToken);
console.log("data => ",dataToUse);

And this is my code in Java using javax.crypto

public String decrypt() {
  String finalToken = null;
  Cipher cipher;
  try {
    String token = "U2FsdGVkX1+6YueVRKp6h0dZfk/a8AC9vyFfAjxD4nb7mXsKrM7rI7xZ0OgrF1sShHYNLMJglz4+67n/I7P+fg==";
    String key = "p80a0811-47db-2c39-bcdd-4t3g5h2d5d1a";
    Key skeySpec = new SecretKeySpec(Arrays.copyOf(key.getBytes(), 16), "AES");
    byte[] iv = Arrays.copyOf(key.getBytes(StandardCharsets.UTF_8), 16);
    IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);
    byte[] bytesToDecrypt = Base64.decodeBase64(token.getBytes());
    cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
    cipher.init(Cipher.DECRYPT_MODE, skeySpec, ivParameterSpec);
    byte[] decrypted = cipher.doFinal(bytesToDecrypt);
    finalToken = new String(decrypted);
    log.info("Decrypt token succesfully {}", finalToken);
  } catch (NoSuchAlgorithmException
      | InvalidAlgorithmParameterException
      | IllegalBlockSizeException
      | NoSuchPaddingException
      | BadPaddingException
      | InvalidKeyException e) {
    e.printStackTrace();
    log.error("Error decrypting");
  }

  return finalToken;
}

I'm not sure I'm setting correctly the key and the iv. With the piece of code above I get this error:

javax.crypto.BadPaddingException: pad block corrupted

If I don't "cut" the key and the iv in order to have 16 bytes I get wrong length error.

Can someone help me to figure out what's wrong please!

The expected result is to get this info in java so then I can manipulate the object:

{name: "Burak", surName: "Bayraktaroglu"}

Topaco · Accepted Answer · 2022-11-28T15:55:10.090

Decryption fails because CryptoJS interprets the key material as password when passed as string (as in the posted code).
In this case, the password and a salt are used to derive the key and IV applying the OpenSSL proprietary key derivation function EVP_BytesToKey().
The random 8 bytes salt is generated during encryption, which returns as result the Base64 encoding of the concatenation of a prefix, the salt and the actual ciphertext. The prefix consists of the ASCII encoding of Salted__.

Therefore, the following steps are necessary in the decryption process:

Determining salt and ciphertext from the CryptoJS return value
Deriving key and IV using password and salt
Decryption of the ciphertext with the derived key and IV

There are several ways to implement the last two steps in Java.
You can find various ports of EVP_BytesToKey() on the web which can be used in conjunction with the native JCA/JCE for decryption. These EVP_BytesToKey() ports are not always reliable, a solid port is this one.
A convenient (and reliable) alternative is BouncyCastle (with its own EVP_BytesToKey() port), described below:

import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.Base64;
import org.bouncycastle.crypto.digests.MD5Digest;
import org.bouncycastle.crypto.engines.AESEngine;
import org.bouncycastle.crypto.generators.OpenSSLPBEParametersGenerator;
import org.bouncycastle.crypto.modes.CBCBlockCipher;
import org.bouncycastle.crypto.paddings.PaddedBufferedBlockCipher;
import org.bouncycastle.crypto.params.ParametersWithIV;

...

// Get salt and ciphertext
String saltCiphertextB64 = "U2FsdGVkX1+6YueVRKp6h0dZfk/a8AC9vyFfAjxD4nb7mXsKrM7rI7xZ0OgrF1sShHYNLMJglz4+67n/I7P+fg==";
byte[] saltCiphertext = Base64.getDecoder().decode(saltCiphertextB64);
ByteBuffer byteBuffer = ByteBuffer.wrap(saltCiphertext);
byte[] prefix = new byte[8];
byte[] salt = new byte[8];
byteBuffer.get(prefix);
byteBuffer.get(salt);
byte[] ciphertext = new byte[byteBuffer.remaining()];
byteBuffer.get(ciphertext);

// Key derivation via EVP_BytesToKey() (using BouncyCastle)
String passwordStr = "p80a0811-47db-2c39-bcdd-4t3g5h2d5d1a";
byte[] password = passwordStr.getBytes(StandardCharsets.UTF_8);
OpenSSLPBEParametersGenerator pbeGenerator = new OpenSSLPBEParametersGenerator(new MD5Digest()); 
pbeGenerator.init(password, salt);
ParametersWithIV parameters = (ParametersWithIV) pbeGenerator.generateDerivedParameters(256, 128); // keySize, ivSize in bits
// FYI: key: ((KeyParameter)parameters.getParameters()).getKey()
//      IV : parameters.getIV()

// Decryption (using BouncyCastle)
PaddedBufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new CBCBlockCipher(new AESEngine()));
cipher.init(false, parameters);
byte[] plaintext = new byte[cipher.getOutputSize(ciphertext.length)];
int length = cipher.processBytes(ciphertext, 0, ciphertext.length, plaintext, 0);
length += cipher.doFinal(plaintext, length);        
String plaintextSr = new String(plaintext, 0, length, StandardCharsets.UTF_8);
System.out.println(plaintextSr); // {"name":"Burak","surName":"Bayraktaroglu"}

CryptoJs decrypt function equivalent in Java

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