import java.nio.file.Files;
import java.nio.file.Paths;

import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import javax.crypto.Cipher;

import java.io.InputStream;
import javax.crypto.CipherInputStream;


public class Huahua {

    public static void main(String...args) throws Exception {
        // pegue a chave
        byte[]sKey=Files.readAllBytes(Paths.get("secret.key"));
        SecretKey key = new SecretKeySpec(sKey, "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, key);
        // pegue a mensagem secreta
        InputStream in = Files.newInputStream(Paths.get("quanto-tem-no-cartao.txt"));
        InputStream cin = new CipherInputStream(in, cipher);
        // jogue num outro arquivo
        Files.copy(cin,Paths.get("quanto-tem-no-cartao-decrypt.txt"));
    }
}