How do i decrypt use AES/GCM/128 between PHP and Java

Question

I'm trying to use java to decrypt the content encrypted through php, but my java code does not work properly. This is the code for the encryption process.

<?php
function aes_gcm_decrypt($content, $secret) {
    $cipher = 'aes-128-gcm';
    $ciphertextwithiv = bin2hex(base64_decode($content));
    $iv = substr($ciphertextwithiv, 0, 24);
    $tag = substr($ciphertextwithiv , -32, 32);
    $ciphertext = substr($ciphertextwithiv, 24, strlen($ciphertextwithiv) - 24 - 32);
    $skey = hex2bin($secret);

    return openssl_decrypt(hex2bin($ciphertext), $cipher, $skey, OPENSSL_RAW_DATA, hex2bin($iv), hex2bin($tag));
}


function aes_gcm_encrypt($data, $secret) {
  $cipher = 'aes-128-gcm';
  $string = is_array($data) ? json_encode($data) : $data;
  $skey = hex2bin($secret);
  $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length($cipher));

  $tag = NULL;
  $content = openssl_encrypt($string, $cipher, $skey, OPENSSL_RAW_DATA, $iv, $tag);

  $str = bin2hex($iv) . bin2hex($content) . bin2hex($tag);
  return base64_encode(hex2bin($str));
}



$content = 'Test text.{123456}';
$secret = '544553544B4559313233343536';
$encryptStr = aes_gcm_encrypt($content, $secret);
print_r("encrypt -> $encryptStr \n");
print_r("\n");

$decryptStr = aes_gcm_decrypt($encryptStr, $secret);
print_r("decrypt -> $decryptStr \n");

result:

encrypt -> Fun3yZTPcHsxBpft+jBZDe2NjGNAs8xUHY21eZswZE4iLKYdBsyER7RwVfFvuQ==

decrypt -> Test text.{123456}

And then this is not my code, so I can't modify it.

Here is the code I'm having for now on my Java side:

import java.security.spec.KeySpec;
import java.util.Base64;
import java.util.Random;
import javax.crypto.*;
import javax.crypto.spec.*;

public class MyTest {

    public static void main(String[] args) throws Exception {
        String secret = "544553544B4559313233343536";
        String encryptStr = "Fun3yZTPcHsxBpft+jBZDe2NjGNAs8xUHY21eZswZE4iLKYdBsyER7RwVfFvuQ==";
        String decryptString = decrypt(encryptStr, secret, 16);
        System.out.println("decryptString: " + decryptString);
    }

    private static String decrypt(String data, String mainKey, int ivLength) throws Exception {
        final byte[] encryptedBytes = Base64.getDecoder().decode(data.getBytes("UTF8"));
        final byte[] initializationVector = new byte[ivLength];
        System.arraycopy(encryptedBytes, 0, initializationVector, 0, ivLength);
        SecretKeySpec secretKeySpec = new SecretKeySpec(generateSecretKeyFromPassword(mainKey, mainKey.length()), "AES");
        GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(128, initializationVector);
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, gcmParameterSpec);
        return new String(cipher.doFinal(encryptedBytes, ivLength, encryptedBytes.length - ivLength), "UTF8");
    }

    private static byte[] generateSecretKeyFromPassword(String password, int keyLength) throws Exception {
        byte[] salt = new byte[keyLength];
        new Random(password.hashCode()).nextBytes(salt);
        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        KeySpec spec = new PBEKeySpec(password.toCharArray(), salt, 65536, 128);
        return factory.generateSecret(spec).getEncoded();
    }
}

This java code will throw an AEADBadTagException.

Exception in thread "main" javax.crypto.AEADBadTagException: Tag mismatch!
    at com.sun.crypto.provider.GaloisCounterMode.decryptFinal(GaloisCounterMode.java:620)
    at com.sun.crypto.provider.CipherCore.finalNoPadding(CipherCore.java:1116)
    at com.sun.crypto.provider.CipherCore.fillOutputBuffer(CipherCore.java:1053)
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:853)
    at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:446)
    at javax.crypto.Cipher.doFinal(Cipher.java:2226)
    at MyTest.decrypt(MyTest.java:24)
    at MyTest.main(MyTest.java:12)

I have searched a lot of information, but still can not solve.

Can you guys possibly help me with building a Java code, that returns the same results?

Thanks in advance!!

Answer 1

I have solved this problem.

This is the correct code:

import java.nio.charset.StandardCharsets;
import java.util.Base64;
import javax.crypto.*;
import javax.crypto.spec.*;

public class MyTest {

    public static final String ALGO = "AES";
    public static final String GCM_ALGO = "AES/GCM/NoPadding";
    public static final int IV_LENGTH = 12;

    public static void main(String[] args) throws Exception {
        String secret = "544553544B4559313233343536";
        String encryptStr = "Fun3yZTPcHsxBpft+jBZDe2NjGNAs8xUHY21eZswZE4iLKYdBsyER7RwVfFvuQ==";
        secret = reformatSecret(secret);
        String decryptStr = decrypt(encryptStr, secret);
        System.out.println("encryptString: " + encryptStr);
        System.out.println("secret: " + secret);
        System.out.println("decryptString: " + decryptStr);
    }

    private static String decrypt(String data, String secret) throws Exception {
        final byte[] encryptedBytes = Base64.getDecoder().decode(data.getBytes(StandardCharsets.UTF_8));
        final byte[] initializationVector = new byte[IV_LENGTH];
        final byte[] key = parseHexStr2Byte(secret);
        System.arraycopy(encryptedBytes, 0, initializationVector, 0, IV_LENGTH);
        SecretKeySpec secretKeySpec = new SecretKeySpec(key, ALGO);
        GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(128, initializationVector);
        Cipher cipher = Cipher.getInstance(GCM_ALGO);
        cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, gcmParameterSpec);
        return new String(cipher.doFinal(encryptedBytes, IV_LENGTH, encryptedBytes.length - IV_LENGTH), StandardCharsets.UTF_8);
    }

    public static String reformatSecret(String secret) {
        if (secret == null || secret.length() < 1) {
            return "";
        }
        int secretLen = secret.length();
        if (secretLen < 32) {
            //padding zero
            StringBuilder str = new StringBuilder(secret);
            while (secretLen < 32) {
                str.append("0");
                secretLen = str.length();
            }
            return str.toString();
        } else {
            //reserved 32 characters
            return secret.substring(0, 32);
        }
    }

    public static byte[] parseHexStr2Byte(String hexStr) {
        int len = hexStr.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(hexStr.charAt(i), 16) << 4) + Character.digit(hexStr.charAt(i+1), 16));
        }
        return data;
    }
}