RSA 工具類。提供加密，解密，生成金鑰對等方法。 

RSA加密原理概述   ：
RSA的安全性依賴於大數的分解，公鑰和私鑰都是兩個大素數（大於100的十進位制位）的函式。
據猜測，從一個金鑰和密文推斷出明文的難度等同於分解兩個大素數的積   
金鑰的產生：   
 1.選擇兩個大素數 p,q ,計算 n=p*q;   
 2.隨機選擇加密金鑰 e ,要求 e 和 (p-1)*(q-1)互質   
 3.利用 Euclid 演算法計算解密金鑰 d , 使其滿足 e*d = 1(mod(p-1)*(q-1)) (其中 n,d 也要互質)   
 4:至此得出公鑰為 (n,e) 私鑰為 (n,d)   
 RSA速度   
 由於進行的都是大數計算，使得RSA最快的情況也比DES慢上100倍，無論 是軟體還是硬體實現。   
 速度一直是RSA的缺陷。一般來說只用於少量資料 加密。

package com.security.rsa;

import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

import javax.crypto.Cipher;
public class RSAsecurity {

public static String src="RSA 加密字串";        
public void priENpubDE() {

    try {
      //1.初始化祕鑰
     KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
     //祕鑰長度
     keyPairGenerator.initialize(512);
     //初始化祕鑰對
     KeyPair keyPair = keyPairGenerator.generateKeyPair();
     //公鑰
     RSAPublicKey rsaPublicKey = (RSAPublicKey) keyPair.getPublic();
     //私鑰
     RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) keyPair.getPrivate();

    //2.私鑰加密，公鑰解密----加密
     //生成私鑰
     PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaPrivateKey.getEncoded());
     KeyFactory keyFactory =KeyFactory.getInstance("RSA");
     PrivateKey privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);
     //Cipher類為加密和解密提供密碼功能，通過getinstance例項化物件
     Cipher cipher =Cipher.getInstance("RSA");
     //初始化加密
     cipher.init(Cipher.ENCRYPT_MODE,privateKey);
     byte[] result = cipher.doFinal(src.getBytes());
     System.out.println("私鑰加密，公鑰解密----加密:"+Base64.encode(result));
     
     
     //3.私鑰加密，公鑰解密----解密
     //生成公鑰
     X509EncodedKeySpec x509EncodedKeySpec = new X509EncodedKeySpec(rsaPublicKey.getEncoded());
     keyFactory=KeyFactory.getInstance("RSA");
     PublicKey publicKey= keyFactory.generatePublic(x509EncodedKeySpec);
     cipher = Cipher.getInstance("RSA");
     //初始化解密
     cipher.init(Cipher.DECRYPT_MODE,publicKey);
     result = cipher.doFinal(result);
     System.out.println("私鑰加密，公鑰解密----解密:"+new String(result));
    } catch (Exception e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
 }
    
         
}
  
  
    
   public void pubENpriDE() {

       try {
         //1.初始化祕鑰
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        //祕鑰長度
        keyPairGenerator.initialize(512);
        //初始化祕鑰對
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        //公鑰
        RSAPublicKey rsaPublicKey = (RSAPublicKey) keyPair.getPublic();
        //私鑰
        RSAPrivateKey rsaPrivateKey = (RSAPrivateKey) keyPair.getPrivate();

       
        
        
        //2.公鑰加密，私鑰解密----加密
       X509EncodedKeySpec x509EncodedKeySpec=new X509EncodedKeySpec(rsaPublicKey.getEncoded());
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    PublicKey publicKey = keyFactory.generatePublic(x509EncodedKeySpec);
     //初始化加密
    //Cipher類為加密和解密提供密碼功能，通過getinstance例項化物件
    Cipher cipher =Cipher.getInstance("RSA");
    cipher.init(Cipher.ENCRYPT_MODE,publicKey);
     //加密字串
    byte[] result = cipher.doFinal(src.getBytes());
     System.out.println("公鑰加密，私鑰解密----加密:"+Base64.encode(result));
     
     //3.公鑰加密，私鑰解密-----解密
   PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(rsaPrivateKey.getEncoded());     
     keyFactory=KeyFactory.getInstance("RSA");
   PrivateKey  privateKey = keyFactory.generatePrivate(pkcs8EncodedKeySpec);
     //初始化解密
     cipher.init(Cipher.DECRYPT_MODE, privateKey);
     //解密字串
     result = cipher.doFinal(result);
     System.out.println("公鑰加密，私鑰解密-----解密:"+new String(result));
     
       } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
       
            
}
}
 

package com.secutiry.rsa;

import com.security.rsa.RSAsecurity;

public class RSAtest {
public static void main(String[] args) {
    RSAsecurity rsAsecurity = new RSAsecurity();
    System.out.println("私鑰加密公鑰解密例：");
    rsAsecurity.priENpubDE();
    System.out.println("公鑰加密私鑰解密例：");
    rsAsecurity.pubENpriDE();
         
}
}
 

原始碼 下載地址

http://download.csdn.net/download/u013400939/8517989點選開啟連結