1、RSA简介

RSA公开密钥密码体制是一种使用不同的加密密钥与解密密钥，“由已知加密密钥推导出解密密钥在计算上是不可行的”密码体制

在公开密钥密码体制中，加密密钥（即公开密钥）PK是公开信息，而解密密钥（即秘密密钥）SK是需要保密的。加密算法E和解密算法D也都是公开的。虽然解密密钥SK是由公开密钥PK决定的，但却不能根据PK计算出SK。RSA应用广泛，解密密钥称为公钥，私钥加密后只能用公钥解密,，当然也可以用公钥加密，用私钥解密。密钥尺寸大，加解密速度慢，一般用来加密少量数据，比如DES加密时使用的密钥。

2、RSA加解密的实现代码

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            KeyValuePair<string, string> encryptDecrypt = RsaEncrypt.GetKeyPair();
            string rsaEn1 = RsaEncrypt.Encrypt("cjavapy", encryptDecrypt.Key);//key是加密的
            Console.WriteLine("rsaEn1 = " + rsaEn1);
            string rsaDe1 = RsaEncrypt.Decrypt(rsaEn1, encryptDecrypt.Value);//value 解密的   不能反过来用的
            Console.WriteLine("rsaDe1 = " + rsaDe1);
            Console.ReadKey();
        }
    }
    /// <summary>
    /// RSA
    /// 可逆非对称加密
    /// 非对称加密算法的优点是密钥管理很方便，缺点是速度慢。
    /// </summary>
    public class RsaEncrypt
    {
        /// <summary>
        /// 获取加密/解密对
        /// 给你一个，是无法推算出另外一个的
        ///
        /// Encrypt   Decrypt
        /// </summary>
        /// <returns>Encrypt   Decrypt</returns>
        public static KeyValuePair<string, string> GetKeyPair()
        {
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
            string publicKey = RSA.ToXmlString(false);
            string privateKey = RSA.ToXmlString(true);
            return new KeyValuePair<string, string>(publicKey, privateKey);
        }
        /// <summary>
        /// 加密：内容+加密key
        /// </summary>
        /// <param name="content"></param>
        /// <param name="encryptKey">加密key</param>
        /// <returns></returns>
        public static string Encrypt(string content, string encryptKey)
        {
            RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
            rsa.FromXmlString(encryptKey);
            UnicodeEncoding ByteConverter = new UnicodeEncoding();
            byte[] DataToEncrypt = ByteConverter.GetBytes(content);
            byte[] resultBytes = rsa.Encrypt(DataToEncrypt, false);
            return Convert.ToBase64String(resultBytes);
        }
        /// <summary>
        /// 解密  内容+解密key
        /// </summary>
        /// <param name="content"></param>
        /// <param name="decryptKey">解密key</param>
        /// <returns></returns>
        public static string Decrypt(string content, string decryptKey)
        {
            byte[] dataToDecrypt = Convert.FromBase64String(content);
            RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
            RSA.FromXmlString(decryptKey);
            byte[] resultBytes = RSA.Decrypt(dataToDecrypt, false);
            UnicodeEncoding ByteConverter = new UnicodeEncoding();
            return ByteConverter.GetString(resultBytes);
        }

        /// <summary>
        /// 可以合并在一起的，，每次产生一组新的密钥
        /// </summary>
        /// <param name="content"></param>
        /// <param name="encryptKey">加密key</param>
        /// <param name="decryptKey">解密key</param>
        /// <returns>加密后结果</returns>
        private static string Encrypt(string content, out string publicKey, out string privateKey)
        {
            RSACryptoServiceProvider rsaProvider = new RSACryptoServiceProvider();
            publicKey = rsaProvider.ToXmlString(false);
            privateKey = rsaProvider.ToXmlString(true);
            UnicodeEncoding ByteConverter = new UnicodeEncoding();
            byte[] DataToEncrypt = ByteConverter.GetBytes(content);
            byte[] resultBytes = rsaProvider.Encrypt(DataToEncrypt, false);
            return Convert.ToBase64String(resultBytes);
        }
    }
}