c#实现验证码功能

一、验证码简介
验证码功能一般是用于防止批量注册的，不少网站为了防止用户利用机器人自动注册、登录、灌水，都采用了验证码技术。所谓验证码，就是将一串随机产生的数字或字母或符号或文字，生成一幅图片， 图片里加上一些干扰象素（防止OCR），由用户肉眼识别其中的验证码信息，输入表单提交网站验证，验证成功后才能使用某项功能。
常见的验证码有如下几种：
1、纯数字验证码，一般为四位随机数字；
2、数字+字母验证码，一般从数字（0~9）和字母(A~Z和a~z)中随机抽出几个字符组成；
3、汉字验证码，相对而言，这种验证码比较少见一点，实现起来也相对复杂一些，但在不少网站中还是可以看到的；
二、验证码的实现
1、纯数字验证码的实现
纯数字验证码的实现相对比较简单，可通过以下两种方法来实现
（1）使用随机数方式，代码如下：

1.         private String GetRandomint(int codeCount)
2.         {
3.             Random random = new Random();
4.             string min = "";
5.             string max = "";
6.             for (int i = 0; i < codeCount; i++)
7.             {
8.                 min +="1";
9.                 max+="9";
10.             }
11.                 return (random.Next(Convert.ToInt32(min),Convert.ToInt32(max)).ToString());
12.         }

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(2)使用随机组合方式，代码如下：

1.         private string CreateRandomCode(int codeCount)
2.         {
3.             string allChar = "0,1,2,3,4,5,6,7,8,9";
4.             string[] allCharArray = allChar.Split(',');
5.             string randomCode = "";
6.             int temp = -1;
7.             Random rand = new Random();
8.             for (int i = 0; i < codeCount; i++)
9.             {
10.                 if (temp != -1)
11.                 {
12.                     rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
13.                 }
14.                 int t = rand.Next(9);
15.                 if (temp == t)
16.                 {
17.                     return CreateRandomCode(codeCount);
18.                 }
19.                 temp = t;
20.                 randomCode += allCharArray[t];
21.             }
22.             return randomCode;
23.         }

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2、数字+字母验证码的实现，代码如下：

1.         private string CreateRandomCode(int codeCount)
2.         {
3.             string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
4.             string[] allCharArray = allChar.Split(',');
5.             string randomCode = "";
6.             int temp = -1;
7.             Random rand = new Random();
8.             for (int i = 0; i < codeCount; i++)
9.             {
10.                 if (temp != -1)
11.                 {
12.                     rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
13.                 }
14.                 int t = rand.Next(61);
15.                 if (temp == t)
16.                 {
17.                     return CreateRandomCode(codeCount);
18.                 }
19.                 temp = t;
20.                 randomCode += allCharArray[t];
21.             }
22.             return randomCode;
23.         }

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3、汉字验证码的实现，代码如下：

1.         /**/
2.         /*
3.     此函数在汉字编码范围内随机创建含两个元素的十六进制字节数组，每个字节数组代表一个汉字，并将
4.     四个字节数组存储在object数组中。
5.     参数：strlength，代表需要产生的汉字个数
6.     */
7.         public static object[] CreateRegionCode(int strlength)
8.         {
9.             //定义一个字符串数组储存汉字编码的组成元素
10.             string[] rBase = new String[16] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };
11.             Random rnd = new Random();
12.             //定义一个object数组用来
13.             object[] bytes = new object[strlength];
15.             /**/
16.             /*每循环一次产生一个含两个元素的十六进制字节数组，并将其放入bject数组中
17.         每个汉字有四个区位码组成
18.         区位码第1位和区位码第2位作为字节数组第一个元素
19.         区位码第3位和区位码第4位作为字节数组第二个元素
20.         */
21.             for (int i = 0; i < strlength; i++)
22.             {
23.                 //区位码第1位
24.                 int r1 = rnd.Next(11, 14);
25.                 string str_r1 = rBase[r1].Trim();
27.                 //区位码第2位
28.                 rnd = new Random(r1 * unchecked((int)DateTime.Now.Ticks) + i);//更换随机数发生器的种子避免产生重复值
29.                 int r2;
30.                 if (r1 == 13)
31.                 {
32.                     r2 = rnd.Next(0, 7);
33.                 }
34.                 else
35.                 {
36.                     r2 = rnd.Next(0, 16);
37.                 }
38.                 string str_r2 = rBase[r2].Trim();
40.                 //区位码第3位
41.                 rnd = new Random(r2 * unchecked((int)DateTime.Now.Ticks) + i);
42.                 int r3 = rnd.Next(10, 16);
43.                 string str_r3 = rBase[r3].Trim();
45.                 //区位码第4位
46.                 rnd = new Random(r3 * unchecked((int)DateTime.Now.Ticks) + i);
47.                 int r4;
48.                 if (r3 == 10)
49.                 {
50.                     r4 = rnd.Next(1, 16);
51.                 }
52.                 else if (r3 == 15)
53.                 {
54.                     r4 = rnd.Next(0, 15);
55.                 }
56.                 else
57.                 {
58.                     r4 = rnd.Next(0, 16);
59.                 }
60.                 string str_r4 = rBase[r4].Trim();
62.                 //定义两个字节变量存储产生的随机汉字区位码
63.                 byte byte1 = Convert.ToByte(str_r1 + str_r2, 16);
64.                 byte byte2 = Convert.ToByte(str_r3 + str_r4, 16);
65.                 //将两个字节变量存储在字节数组中
66.                 byte[] str_r = new byte[] { byte1, byte2 };
68.                 //将产生的一个汉字的字节数组放入object数组中
69.                 bytes.SetValue(str_r, i);
70.             }
71.             return bytes;
72.         }

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三、具体实例
前台代码display.aspx

1. <body>
2.     <form id="form1" runat="server">
3.     <div>
4.       <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
5.         <asp:Image ID="Image1" runat="server" ImageUrl="png.aspx" /><br />
6.         <br />
7.       <asp:Button ID="Button2" runat="server" OnClick="Button2_Click" Text="Button" />
8.         <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">
9.             <asp:ListItem Value="3">默认</asp:ListItem>
10.             <asp:ListItem Value="1">文字</asp:ListItem>
11.             <asp:ListItem Value="2">数字</asp:ListItem>
12.             <asp:ListItem Value="3">混合</asp:ListItem>
13.         </asp:DropDownList></div>
14.     </form>
15. </body>

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后台代码display.cs

1.         protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
2.         {
3.             switch (DropDownList1.SelectedValue)
4.             {
5.                 case "1":
6.                     Image1.ImageUrl = "png.aspx?aa=1";
7.                     break;
8.                 case "2":
9.                     Image1.ImageUrl = "png.aspx?aa=2";
10.                     break;
11.                 case "3":
12.                     Image1.ImageUrl = "png.aspx?aa=3";
13.                     break;
14.             }
15.         }
16.         protected void Button2_Click(object sender, EventArgs e)
17.         {
18.             if (TextBox1.Text == Session["gif"].ToString())
19.                 Response.Write("OK,正确");
20.             else
21.                 Response.Write("验证码不符合");
22.         }

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后台代码png.cs

1.     public partial class png : System.Web.UI.Page
2.     {       
3.         protected void Page_Load(object sender, EventArgs e)
4.         {
5.             switch (Request.QueryString["aa"])
6.             {
7.                 case "1":
8.                     gif = stxt(10);
9.                     Session["gif"] = stxt(10);
10.                     break;
11.                 case "2":
12.                     gif = GetRandomint(4);
13.                     Session["gif"] = GetRandomint(4);
14.                     break;
15.                 case "3":
16.                     gif = CreateRandomCode(4);
17.                     Session["gif"] = CreateRandomCode(4);
18.                     break;
19.                 default:
20.                     gif = CreateRandomCode(4);
21.                     Session["gif"] = CreateRandomCode(4);
22.                     break;
23.             }
24.             CreateImage(Session["gif"].ToString());
25.         }
27.         private String GetRandomint(int codeCount)
28.         {
29.             Random random = new Random();
30.             string min = "";
31.             string max = "";
32.             for (int i = 0; i < codeCount; i++)
33.             {
34.                 min +="1";
35.                 max+="9";
36.             }
37.                 return (random.Next(Convert.ToInt32(min),Convert.ToInt32(max)).ToString());
38.         }
39.         /**/
40.         /*
41.     此函数在汉字编码范围内随机创建含两个元素的十六进制字节数组，每个字节数组代表一个汉字，并将
42.     四个字节数组存储在object数组中。
43.     参数：strlength，代表需要产生的汉字个数
44.     */
45.         public static object[] CreateRegionCode(int strlength)
46.         {
47.             //定义一个字符串数组储存汉字编码的组成元素
48.             string[] rBase = new String[16] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };
49.             Random rnd = new Random();
50.             //定义一个object数组用来
51.             object[] bytes = new object[strlength];
53.             /**/
54.             /*每循环一次产生一个含两个元素的十六进制字节数组，并将其放入bject数组中
55.         每个汉字有四个区位码组成
56.         区位码第1位和区位码第2位作为字节数组第一个元素
57.         区位码第3位和区位码第4位作为字节数组第二个元素
58.         */
59.             for (int i = 0; i < strlength; i++)
60.             {
61.                 //区位码第1位
62.                 int r1 = rnd.Next(11, 14);
63.                 string str_r1 = rBase[r1].Trim();
65.                 //区位码第2位
66.                 rnd = new Random(r1 * unchecked((int)DateTime.Now.Ticks) + i);//更换随机数发生器的种子避免产生重复值
67.                 int r2;
68.                 if (r1 == 13)
69.                 {
70.                     r2 = rnd.Next(0, 7);
71.                 }
72.                 else
73.                 {
74.                     r2 = rnd.Next(0, 16);
75.                 }
76.                 string str_r2 = rBase[r2].Trim();
78.                 //区位码第3位
79.                 rnd = new Random(r2 * unchecked((int)DateTime.Now.Ticks) + i);
80.                 int r3 = rnd.Next(10, 16);
81.                 string str_r3 = rBase[r3].Trim();
83.                 //区位码第4位
84.                 rnd = new Random(r3 * unchecked((int)DateTime.Now.Ticks) + i);
85.                 int r4;
86.                 if (r3 == 10)
87.                 {
88.                     r4 = rnd.Next(1, 16);
89.                 }
90.                 else if (r3 == 15)
91.                 {
92.                     r4 = rnd.Next(0, 15);
93.                 }
94.                 else
95.                 {
96.                     r4 = rnd.Next(0, 16);
97.                 }
98.                 string str_r4 = rBase[r4].Trim();
100.                 //定义两个字节变量存储产生的随机汉字区位码
101.                 byte byte1 = Convert.ToByte(str_r1 + str_r2, 16);
102.                 byte byte2 = Convert.ToByte(str_r3 + str_r4, 16);
103.                 //将两个字节变量存储在字节数组中
104.                 byte[] str_r = new byte[] { byte1, byte2 };
106.                 //将产生的一个汉字的字节数组放入object数组中
107.                 bytes.SetValue(str_r, i);
108.             }
109.             return bytes;
110.         }
111.         private string stxt(int num)
112.         {
113.             Encoding gb = Encoding.GetEncoding("gb2312");
115.             //调用函数产生10个随机中文汉字编码
116.             object[] bytes = CreateRegionCode(num);
117.             string strtxt = "";
119.             //根据汉字编码的字节数组解码出中文汉字
120.             for (int i = 0; i < num; i++)
121.             {
122.                 strtxt += gb.GetString((byte[])Convert.ChangeType(bytes, typeof(byte[])));
123.             }
124.             return strtxt;
125.         }
126.         /// <summary>
127.         /// 这个是使用字母,数字混合
128.         /// </summary>
129.         /// <param name="VcodeNum"></param>
130.         /// <returns></returns>
131.         private string CreateRandomCode(int codeCount)
132.         {
133.             string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z";
134.             string[] allCharArray = allChar.Split(',');
135.             string randomCode = "";
136.             int temp = -1;
137.             Random rand = new Random();
138.             for (int i = 0; i < codeCount; i++)
139.             {
140.                 if (temp != -1)
141.                 {
142.                     rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
143.                 }
144.                 int t = rand.Next(61);
145.                 if (temp == t)
146.                 {
147.                     return CreateRandomCode(codeCount);
148.                 }
149.                 temp = t;
150.                 randomCode += allCharArray[t];
151.             }
152.             return randomCode;
153.         }
155.         private void CreateImage(string checkCode)
156.         {
157.             int iwidth = (int)(checkCode.Length * 20);
158.             System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 25);
159.             Graphics g = Graphics.FromImage(image);
160.             Font f = new System.Drawing.Font("Arial", 10, System.Drawing.FontStyle.Bold);
161.             Brush b = new System.Drawing.SolidBrush(Color.White);
162.             //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);   
163.             g.Clear(Color.Black);
164.             g.DrawString(checkCode, f, b, 3, 3);
165.             Pen blackPen = new Pen(Color.Black, 0);
166.             Random rand = new Random();
167.             //for (int i=0;i<5;i++)   
168.             //{       
169.             //    int y = rand.Next(image.Height); 
170.             //    g.DrawLine(blackPen,0,y,image.Width,y);
171.             //}       
172.             System.IO.MemoryStream ms = new System.IO.MemoryStream();
173.             image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
174.             Response.ClearContent();
175.             Response.ContentType = "image/Jpeg";
176.             Response.BinaryWrite(ms.ToArray());
177.             g.Dispose();
178.             image.Dispose();
179.         }
180.     }

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四、效果图展示
验证码数字
附件: 2009012211325814.jpg
验证码数字+字母
附件: 2009012211340940.jpg
验证码汉字
附件: 2009012211350930.jpg