Crypto using AES-GCM in Java-Python

[suresh-subramaniyan-s]

Need help on decryption logic . currently account numbers are encrypted using java . same needs to be decrypted using python .

i tried with below reference , but it didn't work .

[https://another-coder.medium.com/crypto-using-aes-gcm-in-java-python-591256ad3da7]

java code :

package encryption;

import javax.crypto.Cipher;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.KeySpec;
import java.util.Arrays;
import java.util.Base64;

public class CryptoUtilAesGcm {

    private static final String ALGORITHM = "AES/GCM/NoPadding";
    private static final String FACTORY_INSTANCE = "PBKDF2WithHmacSHA256";
    private static final int TAG_LENGTH_BIT = 128;
    private static final int IV_LENGTH_BYTE = 12;
    private static final int SALT_LENGTH_BYTE = 16;
    private static final String ALGORITHM_TYPE = "AES";
    private static final int KEY_LENGTH = 256;
    private static final int ITERATION_COUNT = 10000;
    private static final Charset UTF_8 = StandardCharsets.UTF_8;

    public static byte[] getRandomNonce(int length) {
        byte[] nonce = new byte[length];
        new SecureRandom().nextBytes(nonce);
        return nonce;
    }

    public static SecretKey getSecretKey(String password, byte[] salt)
            throws NoSuchAlgorithmException, InvalidKeySpecException {
        KeySpec spec = new PBEKeySpec(password.toCharArray(), salt, ITERATION_COUNT, KEY_LENGTH);

        SecretKeyFactory factory = SecretKeyFactory.getInstance(FACTORY_INSTANCE);
        return new SecretKeySpec(factory.generateSecret(spec).getEncoded(), ALGORITHM_TYPE);
    }

    public static String encrypt(String password, String plainMessage) throws Exception {
        //byte[] salt = getRandomNonce(SALT_LENGTH_BYTE);
    	 byte[] salt = { 115, 97, 109, 105, 115, 102, 108, 121};
        SecretKey secretKey = getSecretKey(password, salt);

        // GCM recommends 12 bytes iv
        byte[] iv = getRandomNonce(IV_LENGTH_BYTE);
        Cipher cipher = initCipher(Cipher.ENCRYPT_MODE, secretKey, iv);

        byte[] encryptedMessageByte = cipher.doFinal(plainMessage.getBytes(UTF_8));

        // prefix IV and Salt to cipher text
        byte[] cipherByte = ByteBuffer.allocate(iv.length + salt.length + encryptedMessageByte.length)
                .put(iv)
                .put(salt)
                .put(encryptedMessageByte)
                .array();
        return Base64.getEncoder().encodeToString(cipherByte);
    }

    public static String decrypt(String password, String cipherMessage) throws Exception {
        byte[] decodedCipherByte = Base64.getDecoder().decode(cipherMessage);
        ByteBuffer byteBuffer = ByteBuffer.wrap(decodedCipherByte);
        byte[] iv = null;
	    byte[] encrypted = null;

        int ivLength = byteBuffer.get();
        System.out.println("decryption input"+ ivLength);
	      iv = new byte[ivLength];
	      byteBuffer.get(iv);
	      encrypted = new byte[byteBuffer.remaining()];
	      byteBuffer.get(encrypted);

        byte[] salt = { 115, 97, 109, 105, 115, 102, 108, 121};

        SecretKey secretKey = getSecretKey(password, salt);
        Cipher cipher = initCipher(2, secretKey, iv);

        byte[] decryptedMessageByte = cipher.doFinal(encrypted);
        return new String(decryptedMessageByte, UTF_8);
    }

    private static Cipher initCipher(int mode, SecretKey secretKey, byte[] iv) throws InvalidKeyException, InvalidAlgorithmParameterException, NoSuchPaddingException, NoSuchAlgorithmException {
        Cipher cipher = Cipher.getInstance(ALGORITHM);
        cipher.init(mode, secretKey, new GCMParameterSpec(TAG_LENGTH_BIT, iv));
        return cipher;
    }

    public static void main(String[] args) throws Exception {

        String outputFormat = "%-25s:%s%n";
        String password = "secretkey";
        String message = "M0993000353";

        String cipherText = encrypt(password, message);
        


        System.out.println("------ AES-GCM Encryption ------");
        System.out.printf(outputFormat, "encryption input", message);
        System.out.printf(outputFormat, "encryption output", cipherText);

        String decryptedText = decrypt(password, cipherText);

        System.out.println("\n------ AES-GCM Decryption ------");
        System.out.printf(outputFormat, "decryption input", cipherText);
        System.out.printf(outputFormat, "decryption output", decryptedText);
    }

}