java 使用RSA算法进行加密和解密

一、  生成公钥和私钥

公钥可以对外公开，供其他人加密使用，而把私钥秘密保存用于解密。下面程序产生公钥和私钥，并将他们分别保存在文件中。
import java.io.*;
import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;

public class Skey_RSA{
public static void main(String args[]) throws Exception{
//创建密钥对生成器，指定加密和解密算法为RSA
KeyPairGenerator kpg=KeyPairGenerator.getInstance("RSA");
//指定密钥的长度，初始化密钥对生成器
kpg.initialize(1024);
//生成密钥对
KeyPair kp=kpg.genKeyPair();
//获取公钥
PublicKey pbkey=kp.getPublic();
//获取私钥
PrivateKey prkey=kp.getPrivate();

//保存公钥到文件
FileOutputStream  f1=new FileOutputStream("Skey_RSA_pub.dat");
ObjectOutputStream b1=new  ObjectOutputStream(f1);
       b1.writeObject(pbkey);

//保存私钥到文件
FileOutputStream  f2=new FileOutputStream("Skey_RSA_priv.dat");
ObjectOutputStream b2=new  ObjectOutputStream(f2);
     b2.writeObject(prkey);
}
}

二、使用RSA算法，用公钥对明文加密

import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import javax.crypto.interfaces.*;
import java.security.interfaces.*;
import java.math.*;
import java.io.*;
public class Enc_RSA{
public static void main(String args[]) throws Exception{
//需要加密的明文字符串
String s="Hello World!";
//从文件中读取公钥
FileInputStream f=new FileInputStream("Skey_RSA_pub.dat");
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();
System.out.println("e= "+e);
System.out.println("n= "+n);
//获取明文的大整数
byte ptext[]=s.getBytes("UTF8");
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("Enc_RSA.dat")));
out.write(cs,0,cs.length( ));
out.close( );

}
}

运行结果：
C:/java>java Enc_RSA
e= 65537
n= 13405802078375219658602862966795918240406064464423931951911888365236988242463
33406825151412877079295194644119374029616583316891373732288186538465516523463338
00587304780823025797697373087120665466308717068337942675197170744407800699203571
700904520312857964222781057020371566890161797790968413791779126227980669
c= 47607898340767965145701968255755546566892745661227674225772563975813289594435
28414345875647978484338295878599291349642839959842123774575104652337796795510160
29860635595339439914429389478586533022360831125097334674213734766040265793820856
94641532612227941560162099100409874338485658721364756817554501714726488

C:/java>
三、使用RSA算法，用私钥对密文解密

import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import javax.crypto.interfaces.*;
import java.security.interfaces.*;
import java.math.*;
import java.io.*;
public class Dec_RSA{
public static void main(String args[]) throws Exception{
//读取密文
BufferedReader in=
new BufferedReader(new InputStreamReader(new FileInputStream("Enc_RSA.dat")));
String ctext=in.readLine();
BigInteger c=new BigInteger(ctext);
//获取私钥
FileInputStream f=new FileInputStream("Skey_RSA_priv.dat");
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();
System.out.println("d= "+d);
System.out.println("n= "+n);
//解密明文
BigInteger m=c.modPow(d,n);
System.out.println("m= "+m);
//计算明文对应的字符串并输出。
byte[] mt=m.toByteArray();
System.out.println("PlainText is ");
for(int i=0;i<mt.length;i++){
System.out.print((char) mt[i]);
}
}
}

运行结果：

C:/java>java Dec_RSA
d= 64430162177802259610093989308045506009782293742530938038256352858421144645179
07387915012771839150959006500216983259054143661663562540185437171153217183581928
20085372721431999404588971809332312650448511194624894811079224536652906125419899
15290971295079971714184656932298777888024850821287330626750486312295257
n= 13405802078375219658602862966795918240406064464423931951911888365236988242463
33406825151412877079295194644119374029616583316891373732288186538465516523463338
00587304780823025797697373087120665466308717068337942675197170744407800699203571
700904520312857964222781057020371566890161797790968413791779126227980669
m= 22405534230753928650781647905
PlainText is
Hello World!