SecretDecryptor.java

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.GCMParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;

public class Main {
    public static void main(String[] args) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException {
        Cipher c = Cipher.getInstance("AES/GCM/NoPadding");
        byte[] ivBuffer = new byte[0xc];
        byte[] keyBytes = new byte[] {
                0x63,
                0x39,
                0x30,
                0x61,
                0x66,
                0x30,
                0x35,
                0x37,
                0x65,
                0x32,
                0x35,
                0x37,
                0x34,
                0x61,
                0x66,
                0x30,
                0x39,
                0x37,
                0x37,
                0x33,
                0x66,
                0x65,
                0x35,
                0x37,
                0x34,
                0x63,
                0x65,
                0x39,
                0x35,
                0x34,
                0x37,
                0x30,
        };
        try {
            java.util.Base64.Decoder decoder = Base64.getDecoder();
            byte[] decodedBytes = decoder.decode(args[0]);
            System.arraycopy(decodedBytes, 0, ivBuffer, 0, 0xc);
            byte[] encryptedBytes = new byte[decodedBytes.length - 0xc];
            System.arraycopy(decodedBytes, 12, encryptedBytes,0, decodedBytes.length - 0xc);

            GCMParameterSpec parameterSpec = new GCMParameterSpec(0x60, ivBuffer);
            SecretKeySpec keySpec = new javax.crypto.spec.SecretKeySpec(keyBytes, "AES");

            c.init(javax.crypto.Cipher.DECRYPT_MODE, keySpec, parameterSpec);

            byte[] decryptedBytes = c.doFinal(encryptedBytes);

            String decrypted = new String(decryptedBytes);

            System.out.println("encrypted: " + args[0] + ", decrypted: " + decrypted);
        }
        catch(Exception e)
        {
            System.out.println(e.toString());
        }
    }
}