package cs.lab.demo;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;

import java.security.InvalidAlgorithmParameterException;
import java.security.NoSuchAlgorithmException;
import java.security.Security;
/**
 * DES加密的，文件中共有兩個方法,加密、解密
 * @author 
 * @author 
 */
public class DES {
    private String Algorithm = "DES";
    private KeyGenerator keygen;
    private SecretKey deskey;
    private Cipher c;
    private byte[] cipherByte;

    /**
     * 初始化 DES 實例
     */
    public DES() {
          init();
    }

    public void init() {
        Security.addProvider(new com.sun.crypto.provider.SunJCE());
        try {
               keygen = KeyGenerator.getInstance(Algorithm);
               deskey = keygen.generateKey();
               c = Cipher.getInstance("DES/CBC/NoPadding");
               //c = Cipher.getInstance("DES/ECB/PKCS5Padding");
         }
         catch(NoSuchAlgorithmException ex){
            ex.printStackTrace();
        }
         catch(NoSuchPaddingException ex){
            ex.printStackTrace();
        }
       }

    /**
     * 對 String 進行加密
     * @param str 要加密的數據
     * @return 返回加密后的 byte 數組
     */
     public byte[] createEncryptor(String str) {
        try {
             c.init(Cipher.ENCRYPT_MODE, deskey);
             cipherByte = c.doFinal(str.getBytes());
        }
        catch(java.security.InvalidKeyException ex){
            ex.printStackTrace();
        }
        catch(javax.crypto.BadPaddingException ex){
            ex.printStackTrace();
        }
        catch(javax.crypto.IllegalBlockSizeException ex){
            ex.printStackTrace();
        }
        return cipherByte;
     }

    /**
     * 對 Byte 數組進行解密
     * @param buff 要解密的數據
     * @return 返回加密后的 String
     */
     public String createDecryptor(byte[] buff) {
        try {
           c.init(Cipher.DECRYPT_MODE, deskey, c.getParameters() );
           cipherByte = c.doFinal(buff);
        }
        catch(java.security.InvalidKeyException ex){
            ex.printStackTrace();
        }
        catch(javax.crypto.BadPaddingException ex){
            ex.printStackTrace();
        }
        catch(javax.crypto.IllegalBlockSizeException ex){
            ex.printStackTrace();
        } catch (InvalidAlgorithmParameterException e) {
            e.printStackTrace();
        }
        return (new String(cipherByte));
     }
     public static void main(String[] args) {
        DES des = new DES();
        try{
            byte[] cipher = des.createEncryptor(args[0]);
            System.out.println("Encrypted:"+new String(cipher));//將加密的byte數組以字符串方式顯示
            String plain = des.createDecryptor(cipher);
            System.out.println("Decrypted:"+plain);
        }catch(Exception e){e.printStackTrace();}
    }
}