package com.util;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.interfaces.RSAPrivateCrtKey;
import java.security.interfaces.RSAPublicKey;
import java.util.logging.Level;
import java.util.logging.Logger;


public class RSA {
/**
* 创建密钥对生成器，指定加密和解密算法为RSA
* @param keylen
* @return
*/
public String[] createKey(int keylen) {// 输入密钥长度
String[] output = new String[5]; // 用来存储密钥的e n d p q
try {
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(keylen); // 指定密钥的长度，初始化密钥对生成器
KeyPair kp = kpg.generateKeyPair(); // 生成密钥对
RSAPublicKey puk = (RSAPublicKey) kp.getPublic();
RSAPrivateCrtKey prk = (RSAPrivateCrtKey) kp.getPrivate();
BigInteger e = puk.getPublicExponent();
BigInteger n = puk.getModulus();
BigInteger d = prk.getPrivateExponent();
BigInteger p = prk.getPrimeP();
BigInteger q = prk.getPrimeQ();
output[0] = e.toString();
output[1] = n.toString();
output[2] = d.toString();
output[3] = p.toString();
output[4] = q.toString();
} catch (NoSuchAlgorithmException ex) {
Logger.getLogger(RSAChinese.class.getName()).log(Level.SEVERE, null, ex);
}
return output;
}


/**
* 加密在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。
* @param clearText 明文
* @param eStr 公钥
* @param nStr
* @return
*/
public String encrypt(String clearText, String eStr, String nStr) {
String secretText = new String();

try {
clearText = URLEncoder.encode(clearText,"GBK"); 
byte text[]=clearText.getBytes("GBK");//将字符串转换成byte类型数组，实质是各个字符的二进制形式
BigInteger mm=new BigInteger(text);//二进制串转换为一个大整数
clearText = mm.toString();

BigInteger e = new BigInteger(eStr);
BigInteger n = new BigInteger(nStr);
byte[] ptext = clearText.getBytes("UTF8"); // 获取明文的大整数
BigInteger m = new BigInteger(ptext);
BigInteger c = m.modPow(e, n);
secretText = c.toString();
} catch (UnsupportedEncodingException ex) {
Logger.getLogger(RSAChinese.class.getName()).log(Level.SEVERE, null, ex);
}
return secretText;
}


/**
* 解密
* @param secretText 密文
* @param dStr 私钥
* @param nStr
* @return
*/
public String decrypt(String secretText, String dStr, String nStr) {
StringBuffer clearTextBuffer = new StringBuffer();
BigInteger d = new BigInteger(dStr);// 获取私钥的参数d,n
BigInteger n = new BigInteger(nStr);
BigInteger c = new BigInteger(secretText);
BigInteger m = c.modPow(d, n);// 解密明文
byte[] mt = m.toByteArray();// 计算明文对应的字符串并输出
for (int i = 0; i < mt.length; i++) {
clearTextBuffer.append((char) mt[i]);
}
String temp = clearTextBuffer.toString();//temp为明文的字符串形式
System.out.println("dectemp="+temp);
BigInteger b = new BigInteger(temp);//b为明文的BigInteger类型
byte[] mt1=b.toByteArray();

try {
String clearText = (new String(mt1,"GBK"));
clearText=URLDecoder.decode(clearText,"GBK"); 
return clearText;
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

return null;
}


public static void main(String[] args) {
RSA rsa = new RSA();
String[] str = rsa.createKey(1024);
String clearText = "123abc测试";
String secretText = rsa.encrypt(clearText, str[0], str[1]);
System.out.println("明文是：" + clearText);
System.out.println("密文是：" + secretText);
System.out.println("解密后的明文是：" + rsa.decrypt(secretText, str[2], str[1]));
}
}