非對稱加密算法之DH

一.概述
  （1）非對稱加密算法DH的加解密效率比較低，對要加密的數據長度有着苛刻的要求，這也就是效率換安全吧。
  （2）雖然對稱加密效率高，但密鑰的傳輸需要另外的信道（方式），非對稱加密通過構建本地密鑰來解決密鑰的傳輸問題。

二.加解密過程簡析
  1.發送方A構建密鑰對，A公佈公鑰
  2.接收方B根據A公佈的公鑰構建密鑰對，B公佈公鑰
  3.發送方A使用A構建的私鑰+B公佈的公鑰對數據加密
  4.接收方B使用B構建的私鑰+A公佈的公鑰對數據解密

三.CODE SHOW

package com.sys.common;

import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.X509EncodedKeySpec;

import javax.crypto.Cipher;
import javax.crypto.KeyAgreement;
import javax.crypto.SecretKey;
import javax.crypto.interfaces.DHPublicKey;
import javax.crypto.spec.DHParameterSpec;

import org.apache.commons.codec.binary.Base64;

public class test {

	private static String src="DH加密算法";  
    public static void main(String[] args){  
        jdkDH();  
    }  
  
    public static void jdkDH(){  
        try {  
            //初始化發送方密鑰  
            KeyPairGenerator senderKeyPairGenerator=KeyPairGenerator.getInstance("DH");  
            senderKeyPairGenerator.initialize(512);  
            KeyPair senderKeyPair=senderKeyPairGenerator.generateKeyPair();  
            PrivateKey sendPrivateKey=senderKeyPair.getPrivate();  
            byte[] senderPublicKeyEnc=senderKeyPair.getPublic().getEncoded();  //公佈發送方公鑰
  
            //初始化接收方密鑰 （需要使用發送方公佈的公鑰） 
            KeyFactory receiverKeyFactory=KeyFactory.getInstance("DH");  
            X509EncodedKeySpec x509EncodedKeySpec=new X509EncodedKeySpec(senderPublicKeyEnc);  
            PublicKey receiverPublicKey=receiverKeyFactory.generatePublic(x509EncodedKeySpec);
            DHParameterSpec dhParameterSpec=((DHPublicKey)receiverPublicKey).getParams();  
            KeyPairGenerator receiverKeyPairGenerator=KeyPairGenerator.getInstance("DH");  
            receiverKeyPairGenerator.initialize(dhParameterSpec);  
            KeyPair receiverKeyPair=receiverKeyPairGenerator.generateKeyPair();  
            PrivateKey receiverPrivateKey=receiverKeyPair.getPrivate();  
            byte[] receiverPublicKeyEnc =receiverKeyPair.getPublic().getEncoded();  //公佈接收方公鑰 
  
            //發送方對數據加密 （發送發私鑰+接收方公佈的公鑰）
            KeyFactory senderKeyFactory=KeyFactory.getInstance("DH");   
            x509EncodedKeySpec=new X509EncodedKeySpec(receiverPublicKeyEnc);  
            PublicKey senderPublicKey=senderKeyFactory.generatePublic(x509EncodedKeySpec);
            KeyAgreement senderKeyAgreement=KeyAgreement.getInstance("DH");  
            senderKeyAgreement.init(sendPrivateKey);  
            senderKeyAgreement.doPhase(senderPublicKey, true);  
            Cipher cipher=Cipher.getInstance("DES");
            SecretKey senderDesKey=senderKeyAgreement.generateSecret("DES");  
            cipher.init(Cipher.ENCRYPT_MODE,senderDesKey);  
            byte[] result=cipher.doFinal(src.getBytes());  
            System.out.println("jdk dh encrypt:"+Base64.encodeBase64String(result));  
  
            //接收方對加密數據解密 （接收方私鑰+發送方公佈的公鑰）
            KeyAgreement receiverKeyAgreement = KeyAgreement.getInstance("DH");  
            receiverKeyAgreement.init(receiverPrivateKey);  
            receiverKeyAgreement.doPhase(receiverPublicKey, true);  
            SecretKey receiverDesKey=receiverKeyAgreement.generateSecret("DES");  
            cipher=Cipher.getInstance("DES");  
            cipher.init(Cipher.DECRYPT_MODE,receiverDesKey);  
            result=cipher.doFinal(result);  
            System.out.println("jdk dh encrypt:"+new String(result));  
  
        } catch (Exception e) {  
            e.printStackTrace();  
        }  
    }  
}  

四.輸出結果