package com.sooka.auth.util;

import javax.crypto.Cipher;
import java.nio.charset.StandardCharsets;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;

/**
 * 1.后端使用RSA算法生成一套密钥
 * 2.前端使用接口获取后端公钥
 * 3.后端将公钥传给前端，私钥留在本地服务器
 * 4.前端使用公钥对明文加密，传输到后端
 * 5.后端使用私钥解密，将密文转为明文
 * Author 李猛
 */
public class RsaUtil {

    /**
     * 密钥长度 于原文长度对应 以及越长速度越慢
     */
    private final static int KEY_SIZE = 512;

    /**
     * 随机生成的一套密钥对
     */
    public static SecretKeyBo genKeyPair() throws NoSuchAlgorithmException {
        // KeyPairGenerator类用于生成公钥和私钥对，基于RSA算法生成对象
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
        // 初始化密钥对生成器
        keyPairGen.initialize(KEY_SIZE, new SecureRandom());
        // 生成一个密钥对，保存在keyPair中
        KeyPair keyPair = keyPairGen.generateKeyPair();
        // 得到私钥
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        // 得到公钥
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        String publicKeyString = Base64.getEncoder().encodeToString(publicKey.getEncoded());
        // 得到私钥字符串
        String privateKeyString = Base64.getEncoder().encodeToString(privateKey.getEncoded());

        return new SecretKeyBo()
                .setPrivateKey(privateKeyString)
                .setPublicKey(publicKeyString);
    }

    /**
     * RSA公钥加密
     *
     * @param str    加密字符串
     * @param publicKey 公钥
     * @return 密文
     * @throws Exception 加密过程中的异常信息
     */
    public static String encrypt(String str, String publicKey) throws Exception {
        //base64编码的公钥
        byte[] decoded = Base64.getDecoder().decode(publicKey);
        RSAPublicKey pubKey = (RSAPublicKey) KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(decoded));
        //RSA加密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, pubKey);
        return Base64.getEncoder().encodeToString(cipher.doFinal(str.getBytes(StandardCharsets.UTF_8)));
    }

    /**
     * RSA私钥解密
     *
     * @param str    加密字符串
     * @param privateKey 私钥
     * @return 明文字符串
     * @throws Exception 解密过程中的异常信息
     */
    public static String decrypt(String str, String privateKey) throws Exception {
        //64位解码加密后的字符串
        byte[] inputByte = Base64.getDecoder().decode(str);
        //base64编码的私钥
        byte[] decoded = Base64.getDecoder().decode(privateKey);
        RSAPrivateKey priKey = (RSAPrivateKey) KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(decoded));
        //RSA解密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, priKey);
        return new String(cipher.doFinal(inputByte));
    }

    public static void main(String[] args) throws Exception {
        SecretKeyBo bo = RsaUtil.genKeyPair();
        //公钥
        System.out.println(bo.getPublicKey());
        //私钥
        System.out.println(bo.getPrivateKey());
        //加密
        String str1 = RsaUtil.encrypt("123",bo.getPublicKey());
        System.out.println(str1);
        //解密
        String str2 = RsaUtil.decrypt(str1,bo.getPrivateKey());
        System.out.println(str2);
    }

}