package mimaxue;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.interfaces.RSAPublicKey;
import java.security.interfaces.RSAPrivateCrtKey;
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
    public String[] Skey_RSA(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(RSA.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。
    public String Enc_RSA(String mingwen,String eStr,String nStr){
        String miwen = new String();
        try {
            BigInteger e = new BigInteger(eStr);
            BigInteger n = new BigInteger(nStr);          
            byte[] ptext = mingwen.getBytes("UTF8"); //获取明文的大整数
            BigInteger m = new BigInteger(ptext);
            BigInteger c = m.modPow(e, n);
            miwen = c.toString();
        } catch (UnsupportedEncodingException ex) {
            Logger.getLogger(RSA.class.getName()).log(Level.SEVERE, null, ex);
        }
        return miwen;
    }
    //解密
    public String Dec_RSA(String miwen,String dStr,String nStr){
        StringBuffer mingwen= 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(miwen);        
        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++){
            mingwen.append((char)mt[i]);
        }
        return mingwen.toString();
    }
}