package com.bxuanzhao.key;


import java.math.*;
import java.util.Random;
import java.util.Scanner;

public class RsaFactory {
    public BigInteger publicKeyN, publicKeyE;  //公钥
    private BigInteger privateKey;             //私钥
    BigInteger p, q;
    public RsaFactory(BigInteger p, BigInteger q) {
        this.p = p;
        this.q = q;
        publicKeyN = p.multiply(q);
        this.publicKeyE =  getPublicKeyE();
        this.privateKey = getPrivateKey();
        System.out.println("公钥E: " + publicKeyE);
        System.out.println("公钥N: " + publicKeyN);
        System.out.println("私钥: " + privateKey);
    }
    
    public BigInteger getPublicKeyE () {
        Random rand = new Random();
        publicKeyE = BigInteger.probablePrime(40,rand);
        
        return publicKeyE;
    }
    
    public BigInteger getPrivateKey () {
        BigInteger fn = (p.subtract(BigInteger.ONE)).multiply(q.subtract(BigInteger.ONE));
        privateKey = publicKeyE.modInverse(fn);
        
        return privateKey;
    }
    
    public BigInteger Encryption(BigInteger msg) {
        BigInteger cipher = msg.modPow(publicKeyE, publicKeyN);
        //System.out.println("密文： "+ cipher);
        return cipher;
    }
    
    public BigInteger decryp(BigInteger cipher) {
        BigInteger msg = cipher.modPow(privateKey, publicKeyN);
        //System.out.println("明文：" + msg);
        return msg;
    }
    
    public void rsa(String msg) {
        int m; 
        String s;
        char[] msgArr = msg.toCharArray();
        int length = msgArr.length;
        String[] cipherStr = new String[length];        
        BigInteger cipher[] = new BigInteger[length];
        BigInteger text[] = new BigInteger[length];
        for(int i=0; i<length; i++) {                 //加密成cipherStr
            m = (int)msgArr[i];
            s = String.valueOf(m);
            text[i] = new BigInteger(s);        
            cipher[i] = this.Encryption(text[i]);    
            cipherStr[i] = cipher[i].toString(16);       //加密后的密文
        }
        
        char[] clearMsg = new char[length];
        
        for(int i=0; i<length; i++) {                  //解密
            text[i] = new BigInteger(cipherStr[i],16);
            m = this.decryp(text[i]).intValue();
            clearMsg[i] = (char)m;                    //解密后的明文
        }
        
        System.out.println("加密后的密文为：");
        for(int i=0; i<length; i++) 
            System.out.print(cipherStr[i]);
        
        System.out.println("\n"+"解密后的密文为：");
        for(int i=0; i<length; i++) 
            System.out.print(clearMsg[i]);
    }
    
    public static void main(String[] arg) {
        Random rand = new Random();
        BigInteger p = BigInteger.probablePrime(20,rand);
        BigInteger q = BigInteger.probablePrime(20,rand);
        RsaFactory rsa = new RsaFactory(p, q);
        String mesg;
        System.out.println("输入要加密的消息：");
        Scanner sc = new Scanner(System.in);
        mesg = sc.nextLine();    
        if(mesg != null)
            rsa.rsa(mesg);
        else
            System.out.println("没有需要加密的消息");
    }
}