package main;

import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;

public class CryptoUtil {

    public static Key DEFAULT_KEY = null;

    public static final String DEFAULT_ENCODE_RULES = CryptoUtil.class.getName();

    public
 
 static final String DES = "DES";

    public static void main(String[] args) {
        String a = "20161021142843100001yagnpu123";
        String key = DEFAULT_ENCODE_RULES + "yangpu1212";
        System.out.println(a);
        String strEnc = CryptoUtil.encode(key, a);// 加密字串,返回String的密文
        System.out.println(strEnc);
        String strDes = CryptoUtil.decode(key, strEnc);// 把String 型別的密文解密
 

        System.out.println(strDes);
    }
    static {
        DEFAULT_KEY = obtainKey(DEFAULT_ENCODE_RULES);
    }

    /**
     * 獲得key
     **/
    public static Key obtainKey(String key) {
        if (key == null) {
            return DEFAULT_KEY;
        }
        KeyGenerator generator = null;
        try
 
 {
            generator = KeyGenerator.getInstance(DES);
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        generator.init(new SecureRandom(key.getBytes()));
        Key key1 = generator.generateKey();
        generator = null;
        return key1;
    }

    /**
     * 加密<br>
     * String明文輸入,String密文輸出
     */
    public static String encode(String str) {
        return encode(null, str);
    }

    /**
     * 加密<br>
     * String明文輸入,String密文輸出
     */
    public static String encode(String key, String str) {
        return byteToString(obtainEncode(key, str.getBytes()));
    }

    /**
     * 解密<br>
     * 以String密文輸入,String明文輸出
     */
    public static String decode(String str) {
        return decode(null, str);
    }

    /**
     * 解密<br>
     * 以String密文輸入,String明文輸出
     */
    public static String decode(String key, String str) {
        return new String(obtainDecode(key, stringToByte(str)));
    }

    /**
     * 加密<br>
     * 以byte[]明文輸入,byte[]密文輸出
     */
    private static byte[] obtainEncode(String key, byte[] str) {
        byte[] byteFina = null;
        Cipher cipher;
        try {
            Key key1 = obtainKey(key);
            cipher = Cipher.getInstance(DES);
            cipher.init(Cipher.ENCRYPT_MODE, key1);
            byteFina = cipher.doFinal(str);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            cipher = null;
        }
        return byteFina;
    }

    /**
     * 解密<br>
     * 以byte[]密文輸入,以byte[]明文輸出
     */
    private static byte[] obtainDecode(String key, byte[] str) {
        Cipher cipher;
        byte[] byteFina = null;
        try {
            Key key1 = obtainKey(key);
            cipher = Cipher.getInstance(DES);
            cipher.init(Cipher.DECRYPT_MODE, key1);
            byteFina = cipher.doFinal(str);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            cipher = null;
        }
        return byteFina;
    }

    /**
     * 將byte轉換成string
     */
    public static String byteToString(byte[] b) {
        // 轉成16進位制字串
        StringBuilder sb = new StringBuilder();
        String stmp = "";
        for (int n = 0; n < b.length; n++) {
            // 整數轉成十六進位制表示
            stmp = Integer.toHexString(b[n] & 0XFF);
            if (stmp.length() == 1) {
                sb.append("0" + stmp);
            } else {
                sb.append(stmp);
            }
        }
        return sb.toString().toUpperCase(); // 轉成大寫
    }

    /**
     * 將string轉換成byte
     */
    public static byte[] stringToByte(String str) {
        byte[] b = str.getBytes();
        if ((b.length % 2) != 0)
            throw new IllegalArgumentException(b + ":length is not even numbers");
        byte[] b2 = new byte[b.length / 2];
        for (int n = 0; n < b.length; n += 2) {
            String item = new String(b, n, 2);
            // 兩位一組，表示一個位元組,把這樣表示的16進位制字串，還原成一個進位制位元組
            b2[n / 2] = (byte) Integer.parseInt(item, 16);
        }
        return b2;
    }
}