在之前的項目中，如果有需要使用驗證碼，基本都是自己用GDI+畫圖出來，簡單好用，但是卻也存在了一些小問題，首先若較少干擾線，則安全性不是很高，驗證碼容易被機器識別，若多畫太多干擾線條，機器人識別率下降的同時，人眼的識別率也同步下降（震驚哭）。更為重要的是，GDI+繪制的驗證碼一般來說也不會很美觀，如果做一個炫酷的登陸界面卻配了這樣一個驗證碼，畫風詭異，丑到極致。

      再后來瀏覽網(wǎng)頁的過程中，發(fā)現(xiàn)很多很多網(wǎng)站項目中都使用了一種叫極驗驗證的驗證碼，采用移動滑塊的方式進行驗證，方便美觀。而一番搜索之后了解到，官方提供的免費版也足以應付我手頭的大多數(shù)項目了，不禁想把在MVC學習過程中試著使用極驗驗證來作為登錄的驗證碼。

      極驗官方提供了C#的SDK和Demo供開發(fā)者參考，不過是Webform版本的，可讀性不是很高，而現(xiàn)在使用Webform進行網(wǎng)站開發(fā)的也基本消失了，我將在官方Webform代碼的基礎(chǔ)上，將其用在ASP.NET MVC程序中。

注冊極驗

到極驗官網(wǎng)注冊賬號之后進入后臺管理界面，點擊添加驗證

添加后我們可以得到ID和KEY

完成驗證邏輯

1. 首先我們需要引入官方的Geetestlib類

using System;using System.Collections;using System.Collections.Generic;using System.Linq;using System.Text;using System.Security.Cryptography;using System.Net;using System.IO;namespace PMS.WebApp.Models{ /// <summary> /// GeetestLib 極驗驗證C# SDK基本庫 /// </summary> public class GeetestLib {  /// <summary>  /// SDK版本號  /// </summary>  public const String version = "3.2.0";  /// <summary>  /// SDK開發(fā)語言  /// </summary>  public const String sdkLang = "csharp";  /// <summary>  /// 極驗驗證API URL  /// </summary>  protected const String apiUrl = "http://api.geetest.com";  /// <summary>  /// register url  /// </summary>  protected const String registerUrl = "/register.php";  /// <summary>  /// validate url  /// </summary>  protected const String validateUrl = "/validate.php";  /// <summary>  /// 極驗驗證API服務狀態(tài)Session Key  /// </summary>  public const String gtServerStatusSessionKey = "gt_server_status";  /// <summary>  /// 極驗驗證二次驗證表單數(shù)據(jù) Chllenge  /// </summary>  public const String fnGeetestChallenge = "geetest_challenge";  /// <summary>  /// 極驗驗證二次驗證表單數(shù)據(jù) Validate  /// </summary>  public const String fnGeetestValidate = "geetest_validate";  /// <summary>  /// 極驗驗證二次驗證表單數(shù)據(jù) Seccode  /// </summary>  public const String fnGeetestSeccode = "geetest_seccode";  private String userID = "";  private String responseStr = "";  private String captchaID = "";  private String privateKey = "";  /// <summary>  /// 驗證成功結(jié)果字符串  /// </summary>  public const int successResult = 1;  /// <summary>  /// 證結(jié)失敗驗果字符串  /// </summary>  public const int failResult = 0;  /// <summary>  /// 判定為機器人結(jié)果字符串  /// </summary>  public const String forbiddenResult = "forbidden";  /// <summary>  /// GeetestLib構(gòu)造函數(shù)  /// </summary>  /// <param name="publicKey">極驗驗證公鑰</param>  /// <param name="privateKey">極驗驗證私鑰</param>  public GeetestLib(String publicKey, String privateKey)  {   this.privateKey = privateKey;   this.captchaID = publicKey;  }  private int getRandomNum()  {   Random rand =new Random();   int randRes = rand.Next(100);   return randRes;  }  /// <summary>  /// 驗證初始化預處理  /// </summary>  /// <returns>初始化結(jié)果</returns>  public Byte preProcess()  {   if (this.captchaID == null)   {    Console.WriteLine("publicKey is null!");   }   else   {    String challenge = this.registerChallenge();    if (challenge.Length == 32)    {     this.getSuccessPreProcessRes(challenge);     return 1;    }    else    {     this.getFailPreProcessRes();     Console.WriteLine("Server regist challenge failed!");    }   }   return 0;  }  public Byte preProcess(String userID)  {   if (this.captchaID == null)   {    Console.WriteLine("publicKey is null!");   }   else   {    this.userID = userID;    String challenge = this.registerChallenge();    if (challenge.Length == 32)    {     this.getSuccessPreProcessRes(challenge);     return 1;    }    else    {     this.getFailPreProcessRes();     Console.WriteLine("Server regist challenge failed!");    }   }   return 0;  }  public String getResponseStr()  {   return this.responseStr;  }  /// <summary>  /// 預處理失敗后的返回格式串  /// </summary>  private void getFailPreProcessRes()  {   int rand1 = this.getRandomNum();   int rand2 = this.getRandomNum();   String md5Str1 = this.md5Encode(rand1 + "");   String md5Str2 = this.md5Encode(rand2 + "");   String challenge = md5Str1 + md5Str2.Substring(0, 2);   this.responseStr = "{" + string.Format(     "/"success/":{0},/"gt/":/"{1}/",/"challenge/":/"{2}/"", 0,    this.captchaID, challenge) + "}";  }  /// <summary>  /// 預處理成功后的標準串  /// </summary>  private void getSuccessPreProcessRes(String challenge)  {   challenge = this.md5Encode(challenge + this.privateKey);   this.responseStr ="{" + string.Format(    "/"success/":{0},/"gt/":/"{1}/",/"challenge/":/"{2}/"", 1,     this.captchaID, challenge) + "}";  }  /// <summary>  /// failback模式的驗證方式  /// </summary>  /// <param name="challenge">failback模式下用于與validate一起解碼答案， 判斷驗證是否正確</param>  /// <param name="validate">failback模式下用于與challenge一起解碼答案， 判斷驗證是否正確</param>  /// <param name="seccode">failback模式下，其實是個沒用的參數(shù)</param>  /// <returns>驗證結(jié)果</returns>  public int failbackValidateRequest(String challenge, String validate, String seccode)  {   if (!this.requestIsLegal(challenge, validate, seccode)) return GeetestLib.failResult;   String[] validateStr = validate.Split('_');   String encodeAns = validateStr[0];   String encodeFullBgImgIndex = validateStr[1];   String encodeImgGrpIndex = validateStr[2];   int decodeAns = this.decodeResponse(challenge, encodeAns);   int decodeFullBgImgIndex = this.decodeResponse(challenge, encodeFullBgImgIndex);   int decodeImgGrpIndex = this.decodeResponse(challenge, encodeImgGrpIndex);   int validateResult = this.validateFailImage(decodeAns, decodeFullBgImgIndex, decodeImgGrpIndex);   return validateResult;  }  private int validateFailImage(int ans, int full_bg_index, int img_grp_index)  {   const int thread = 3;   String full_bg_name = this.md5Encode(full_bg_index + "").Substring(0, 10);   String bg_name = md5Encode(img_grp_index + "").Substring(10, 10);   String answer_decode = "";   for (int i = 0;i < 9; i++)   {    if (i % 2 == 0) answer_decode += full_bg_name.ElementAt(i);    else if (i % 2 == 1) answer_decode += bg_name.ElementAt(i);   }   String x_decode = answer_decode.Substring(4);   int x_int = Convert.ToInt32(x_decode, 16);   int result = x_int % 200;   if (result < 40) result = 40;   if (Math.Abs(ans - result) < thread) return GeetestLib.successResult;   else return GeetestLib.failResult;  }  private Boolean requestIsLegal(String challenge, String validate, String seccode)  {   if (challenge.Equals(string.Empty) || validate.Equals(string.Empty) || seccode.Equals(string.Empty)) return false;   return true;  }  /// <summary>  /// 向gt-server進行二次驗證  /// </summary>  /// <param name="challenge">本次驗證會話的唯一標識</param>  /// <param name="validate">拖動完成后server端返回的驗證結(jié)果標識字符串</param>  /// <param name="seccode">驗證結(jié)果的校驗碼，如果gt-server返回的不與這個值相等則表明驗證失敗</param>  /// <returns>二次驗證結(jié)果</returns>  public int enhencedValidateRequest(String challenge, String validate, String seccode)  {   if (!this.requestIsLegal(challenge, validate, seccode)) return GeetestLib.failResult;   if (validate.Length > 0 && checkResultByPrivate(challenge, validate))   {    String query = "seccode=" + seccode + "&sdk=csharp_" + GeetestLib.version;    String response = "";    try    {     response = postValidate(query);    }    catch (Exception e)    {     Console.WriteLine(e);    }    if (response.Equals(md5Encode(seccode)))    {     return GeetestLib.successResult;    }   }   return GeetestLib.failResult;  }  public int enhencedValidateRequest(String challenge, String validate, String seccode, String userID)  {   if (!this.requestIsLegal(challenge, validate, seccode)) return GeetestLib.failResult;   if (validate.Length > 0 && checkResultByPrivate(challenge, validate))   {    String query = "seccode=" + seccode + "&user_id=" + userID + "&sdk=csharp_" + GeetestLib.version;    String response = "";    try    {     response = postValidate(query);    }    catch (Exception e)    {     Console.WriteLine(e);    }    if (response.Equals(md5Encode(seccode)))    {     return GeetestLib.successResult;    }   }   return GeetestLib.failResult;  }  private String readContentFromGet(String url)  {   try   {    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);    request.Timeout = 20000;    HttpWebResponse response = (HttpWebResponse)request.GetResponse();    Stream myResponseStream = response.GetResponseStream();    StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));    String retString = myStreamReader.ReadToEnd();    myStreamReader.Close();    myResponseStream.Close();    return retString;   }   catch   {    return "";     }  }  private String registerChallenge()  {   String url = "";   if (string.Empty.Equals(this.userID))   {    url = string.Format("{0}{1}?gt={2}", GeetestLib.apiUrl, GeetestLib.registerUrl, this.captchaID);   }   else   {    url = string.Format("{0}{1}?gt={2}&user_id={3}", GeetestLib.apiUrl, GeetestLib.registerUrl, this.captchaID, this.userID);   }   string retString = this.readContentFromGet(url);   return retString;  }  private Boolean checkResultByPrivate(String origin, String validate)  {   String encodeStr = md5Encode(privateKey + "geetest" + origin);   return validate.Equals(encodeStr);  }  private String postValidate(String data)  {   String url = string.Format("{0}{1}", GeetestLib.apiUrl, GeetestLib.validateUrl);   HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);   request.Method = "POST";   request.ContentType = "application/x-www-form-urlencoded";   request.ContentLength = Encoding.UTF8.GetByteCount(data);   // 發(fā)送數(shù)據(jù)   Stream myRequestStream = request.GetRequestStream();   byte[] requestBytes = System.Text.Encoding.ASCII.GetBytes(data);   myRequestStream.Write(requestBytes, 0, requestBytes.Length);   myRequestStream.Close();   HttpWebResponse response = (HttpWebResponse)request.GetResponse();   // 讀取返回信息   Stream myResponseStream = response.GetResponseStream();   StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));   string retString = myStreamReader.ReadToEnd();   myStreamReader.Close();   myResponseStream.Close();   return retString;  }  private int decodeRandBase(String challenge)  {   String baseStr = challenge.Substring(32, 2);   List<int> tempList = new List<int>();   for(int i = 0; i < baseStr.Length; i++)   {    int tempAscii = (int)baseStr[i];    tempList.Add((tempAscii > 57) ? (tempAscii - 87)     : (tempAscii - 48));   }   int result = tempList.ElementAt(0) * 36 + tempList.ElementAt(1);   return result;  }  private int decodeResponse(String challenge, String str)  {   if (str.Length>100) return 0;   int[] shuzi = new int[] { 1, 2, 5, 10, 50};   String chongfu = "";   Hashtable key = new Hashtable();   int count = 0;   for (int i=0;i<challenge.Length;i++)   {    String item = challenge.ElementAt(i) + "";    if (chongfu.Contains(item)) continue;    else    {     int value = shuzi[count % 5];     chongfu += item;     count++;     key.Add(item, value);    }   }   int res = 0;   for (int i = 0; i < str.Length; i++) res += (int)key[str[i]+""];   res = res - this.decodeRandBase(challenge);   return res;  }  private String md5Encode(String plainText)  {   MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();   string t2 = BitConverter.ToString(md5.ComputeHash(UTF8Encoding.Default.GetBytes(plainText)));   t2 = t2.Replace("-", "");   t2 = t2.ToLower();   return t2;  } }}