TestDecrypt.java

import java.util.Base64;
import javax.crypto.Cipher;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;

public class TestDecrypt {
    private static byte[] decodeBase64Url(String value) {
        return java.util.Base64.getUrlDecoder().decode(value);
    }

    private static byte[] derivePasswordKey(String password, byte[] salt, int iterations) throws Exception {
        PBEKeySpec spec = new PBEKeySpec(password.toCharArray(), salt, iterations, 256);
        SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        return factory.generateSecret(spec).getEncoded();
    }

    private static byte[] decryptAesGcm(byte[] key, byte[] nonce, byte[] ciphertext) throws Exception {
        Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        SecretKeySpec secretKey = new SecretKeySpec(key, "AES");
        GCMParameterSpec spec = new GCMParameterSpec(128, nonce);
        cipher.init(Cipher.DECRYPT_MODE, secretKey, spec);
        return cipher.doFinal(ciphertext);
    }

    public static void main(String[] args) throws Exception {
        String password = "testpass";
        int iterations = 200000;
        String salt = "xACtL-dghKq_eIGZJSsvkw==";
        String nonce = "lco8UtNSSjigk6d9";
        String ciphertext = "aP4dXouK-OHeMUAz7ITxI5e-fDJPoDE14pIswZTKajx_rLKJ7bQ3ry5OqlXM2gZflDq44M39-duGZUhM2x_-TCpK6SEdtbHBWzrIlz-x5BsievrAhfWNLzaxChxWcQ7_fgzOkIBLv5tBzLsRZb8ajoRb7obNNfUQ9bcc_iab5lDMpt7AWRylqgfqFfF5ExHOAncAF9keiU9RySiL5VGQwCOh_I0xgYDxXxU58_wknoYY1gLScOjXz-SAoFNoxRWT6uwViphtyijx2kr2jPI48n0GL0DBrwSQPWo0ZrLAiOseJkmm2dbmhjA4DSvhAN03gbx2C6oeNPsK-lrz8hm-h2lyu8IaOKzJilSQYMCmsTNIhDfJ0OiliQDisQqmjhjsjpSpROYrDVY6uXa3f0nbeS_ajIojFuZZ9qT2Dmc1d2TSDpFTe88Ab50haoG5kciS93JCa4OR6qJkhc23jIcybxzla8cv5bkpHN_f4r2W4QrAr2PdLJTy3bO3DYUJKBJwoHGIDw==";

        byte[] saltBytes = decodeBase64Url(salt);
        byte[] nonceBytes = decodeBase64Url(nonce);
        byte[] cipherBytes = decodeBase64Url(ciphertext);

        byte[] key = derivePasswordKey(password, saltBytes, iterations);
        byte[] plaintext = decryptAesGcm(key, nonceBytes, cipherBytes);
        System.out.println(new String(plaintext, java.nio.charset.StandardCharsets.UTF_8));
    }
}