生成密钥，并保存

RSACryptoServiceProvider crypt=new RSACryptoServiceProvider();
   string publickey=crypt.ToXmlString(false);//（公钥）
   string privatekey=crypt.ToXmlString(true);
   crypt.Clear();
   StreamWriter one=new StreamWriter(@"c:/a.txt",true,UTF8Encoding.UTF8);
   one.Write(publickey);
   StreamWriter two=new StreamWriter(@"c:/b.txt",true,UTF8Encoding.UTF8);
   two.Write(privatekey);
   one.Flush();
   two.Flush();
   one.Close();
   two.Close();
   Console.WriteLine("成功保存公匙和密匙！");