java实用RSA的简单例子

 

import  java.io.BufferedReader; 
import  java.io.BufferedWriter;
import  java.io.FileInputStream; 
import  java.io.FileOutputStream; 
import  java.io.IOException;
import  java.io.InputStreamReader; 
import  java.io.ObjectInputStream;
import  java.io.ObjectOutputStream; 
import  java.io.OutputStreamWriter;
import  java.math.BigInteger;
import  java.security.KeyPair;
import  java.security.KeyPairGenerator;
import  java.security.NoSuchAlgorithmException;
import  java.security.PrivateKey;
import  java.security.PublicKey;
import  java.security.SecureRandom;
import  java.security.interfaces.RSAPrivateKey;
import  java.security.interfaces.RSAPublicKey;

public   class  RSA
{
     public   static   void  main(String[] args)  throws  NoSuchAlgorithmException, IOException, ClassNotFoundException
    {
        KeyPair pair  =  generateKeyPair();
        PrivateKey privateKey  =  pair.getPrivate();
        PublicKey publicKey  =  pair.getPublic();

         //  Save Pirvate Key
        FileOutputStream f1  =   new  FileOutputStream( " private.ppk " );
        ObjectOutputStream b1  =   new  ObjectOutputStream(f1);
        b1.writeObject(privateKey);

         //  Save Public Key
        FileOutputStream f2  =   new  FileOutputStream( " public.ppk " );
        ObjectOutputStream b2  =   new  ObjectOutputStream(f2);
        b2.writeObject(publicKey);

        encrypt();
        
        decrypt();

    }

     public   static   void  encrypt()  throws  IOException, ClassNotFoundException
    {
        String msg  =   " Hello World! " ;

        FileInputStream f  =   new  FileInputStream( " public.ppk " );
        ObjectInputStream b  =   new  ObjectInputStream(f);
        RSAPublicKey pbk  =  (RSAPublicKey) b.readObject();

         //  RSA算法是使用整数进行加密的，在RSA公钥中包含有两个整数信息：e和n。对于明文数字m,计算密文的公式是m的e次方再与n求模。
        BigInteger e  =  pbk.getPublicExponent();
        BigInteger n  =  pbk.getModulus();

         //  获取明文的大整数
         byte  ptext[]  =  msg.getBytes( " utf-8 " );
        BigInteger m  =   new  BigInteger(ptext);

         //  加密明文
        BigInteger c  =  m.modPow(e, n);
        
         //  打印密文c
        System.out.println( " c=  "   +  c);
        
         //  将密文以字符串形式保存在文件中
        String cs  =  c.toString();
        BufferedWriter out  =   new  BufferedWriter( new  OutputStreamWriter( new  FileOutputStream( " encrypt.dat " ),  " utf-8 " ));
        out.write(cs,  0 , cs.length());
        out.close();

    }

     public   static   void  decrypt()  throws  IOException, ClassNotFoundException
    {
        BufferedReader in  =   new  BufferedReader( new  InputStreamReader( new  FileInputStream( " encrypt.dat " ),  " utf-8 " ));
        String ctext  =  in.readLine();
        BigInteger c  =   new  BigInteger(ctext);
        
         //  获取私钥
        FileInputStream f  =   new  FileInputStream( " private.ppk " );
        ObjectInputStream b  =   new  ObjectInputStream(f);
        RSAPrivateKey prk  =  (RSAPrivateKey) b.readObject();
        
         //  获取私钥的参数d,n
        BigInteger d  =  prk.getPrivateExponent();
        BigInteger n  =  prk.getModulus();
            
         //  解密明文
        BigInteger m  =  c.modPow(d, n);
        
        
         //  计算明文对应的字符串并输出。
         byte [] mt  =  m.toByteArray();
        System.out.println( " PlainText is  "   +   new  String(mt,  " utf-8 " ));
        
    }

     public   static  KeyPair generateKeyPair()  throws  NoSuchAlgorithmException
    {
        KeyPairGenerator keyPairGen  =  KeyPairGenerator.getInstance( " RSA " );
         final   int  KEY_SIZE  =   1024 ;
        keyPairGen.initialize(KEY_SIZE,  new  SecureRandom());
        KeyPair keyPair  =  keyPairGen.genKeyPair();
         return  keyPair;
    }

}

 

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