JAVA中RSA的类
JAVA中RSA的类

别处摘的，先保存下来

package com.google.algorithm;
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;
}

}