<xml> 
<ToUserName><![CDATA[{0}]]></ToUserName> 
<FromUserName><![CDATA[{1}]]></FromUserName> 
<CreateTime>{2}</CreateTime> 
<MsgType><![CDATA[text]]></MsgType> 
<Content><![CDATA[{3}]]></Content> 
</xml>

<xml> 
<ToUserName><![CDATA[{0}]]></ToUserName> 
<FromUserName><![CDATA[{1}]]></FromUserName> 
<CreateTime>{2}</CreateTime> 
<MsgType><![CDATA[image]]></MsgType> 
<Image> 
<MediaId><![CDATA[{3}]]></MediaId> 
</Image> 
</xml>

responseContent = string.Format(ReplyType.Message_Text, 
 FromUserName.InnerText, 
 ToUserName.InnerText, 
DateTime.Now.Ticks, 
String.IsNullOrEmpty(reply)"Sorry,I can not follow you." :reply);

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Common
{
  public class WeChatSecurityHelper
  {
    /// <summary>
    /// 定义Token，与微信公共平台上的Token保持一致
    /// </summary>
    private const string Token = "StupidMe";
    /// <summary>
    /// AppId 要与 微信公共平台 上的 AppId 保持一致
    /// </summary>
    private const string AppId = "11111111111";
    /// <summary>
    /// 加密用 
    /// </summary>
    private const string AESKey = "pvX2KZWRLQSkUAbvArgLSAxCwTtxgFWF3XOnJ9iEUMG";

    private static Tencent.WXBizMsgCrypt wxcpt = new Tencent.WXBizMsgCrypt(Token, AESKey, AppId);
    private string signature,timestamp,nonce;
    private static LogHelper logger = new LogHelper(typeof(WeChatSecurityHelper));


    public WeChatSecurityHelper(string signature, string timestamp, string nonce)
    {
      this.signature = signature;
      this.timestamp = timestamp;
      this.nonce = nonce;
    }

    /// <summary>
    /// 加密消息
    /// </summary>
    /// <param name="msg">要加密的消息</param>
    /// <returns>加密后的消息</returns>
    public string EncryptMsg(string msg)
    {
      string encryptMsg="";
      int result = wxcpt.EncryptMsg(msg, timestamp, nonce, ref encryptMsg);
      if (result == 0)
      {
        return encryptMsg;
      }
      else
      {
        logger.Error("消息加密失败");
        return "";
      }
    }

    /// <summary>
    /// 解密消息
    /// </summary>
    /// <param name="msg">消息体</param>
    /// <returns>明文消息</returns>
    public string DecryptMsg(string msg)
    {
      string decryptMsg = "";
      int result = wxcpt.DecryptMsg(signature, timestamp, nonce, msg,ref decryptMsg);
      if (result != 0)
      {
        logger.Error("消息解密失败,result:"+result);
      }
      return decryptMsg;
    }
  }
}