Example how to encrypt a message with a provided secret using the Data Encryption Standard algorithm. The message is writen to a given file. The provided secret is required to have exactly 8 characters.

MessageDESEncrypter.java

import java.io.FileOutputStream;
import java.io.OutputStream;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;

import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;

public class MessageDESEncrypter {
    
    private static final String MESSAGE = System.getProperty("message", "Hello encrypted world");
    private static final String PASSWD = System.getProperty("passwd", "__secret");
    private static final String SINK = System.getProperty("sink", "target/test.secured");
    
    public static void main(String[] args) throws Exception {
        
        FileOutputStream out = new FileOutputStream(SINK);
        Cipher cipher = createCipher(PASSWD.getBytes());
        
        encode(MESSAGE.getBytes(), out, cipher);
        
    }
    
    static Cipher createCipher(byte[] secret) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
        Cipher cipher = Cipher.getInstance("DES");
        Key key = new SecretKeySpec(secret, "DES");
        cipher.init(Cipher.ENCRYPT_MODE, key);
        return cipher;
    }

    static void encode(byte[] bytes, OutputStream out, Cipher cipher) throws Exception {
        
        try ( OutputStream cos = new CipherOutputStream(out, cipher)) {
            cos.write(bytes);
        }
    }
}