With this trick you can quickly create a security code system for your website.
To create a security code we will follow the following steps:
We have to add in the form that we want to insert the security code the following controls:
- An image (where your scr will be /AntiRobots.aspx)
- A text type input, with an id= type= frm_Code_Security
In the VB code of the registration page we will declare a variable called bAntiBots
#Region “Members”
Dim bAntiBots As Boolean = False
#End Region
In the Page_Load:
If Not Is PostBack Then
Session(“AntiBots”) = GenerateRandomCode()
else
‘We check the antibots code
If frm_Security_Code.Value = Session(“AntiBots”).ToString() Then
bAntiBots = True
else
bAntiBots = False
Me.Session(“AntiBots”) = GenerateRandomCode()
End If
End If
We need to create the GenerateRandomCode function to generate a random security code
#Region “GenerateRandomCode”
Private Function GenerateRandomCode() As String
Dim random As New Random
Dim s As String = “”
Dim i As Int32 = 0
Dim iChr As Int32
While(i <; 6)
iChr = random.Next(48, 90)
While iChr >; 57 And iChr <; 65
iChr = random.Next(48, 90)
End While
s = String.Concat(s, Chr(iChr).ToString())
i = i + 1
End While
Returns
End Function
#End Region
To continue, we will need to create the class in charge of creating, manipulating and deforming the security code generated in the image.
Import System
Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Drawing.Imaging
Imports System.Drawing.Text
Public Class ImageAntiBots
Dim m_text As String
Dim m_width As Int32
Dim m_height As Int32
Dim m_familyName As String
Dim m_image As Bitmap
Dim m_random As New Random
#Region “Read Properties”
Public ReadOnly Property Text() As String
Get
Return m_text
End Get
End Property
Public ReadOnly Property Width() As Int32
Get
m_width
End Get
End Property
Public ReadOnly Property Height() As Int32
Get
m_height
End Get
End Property
Public ReadOnly Property Image() As Bitmap
Get
Return m_image
End Get
End Property
#End Region
Public Sub New(ByVal s As String, ByVal width As Int32, ByVal height As Int32)
me.m_text = yes
Me.SetDimensions(width, height)
Me.GenerateImage()
End Sub
Public Sub New(ByVal s As String, ByVal width As Int32, ByVal height As Int32, ByVal familyName As String)
me.m_text = yes
Me.SetDimensions(width, height)
Me.SetFamilyName(familyName)
Me.GenerateImage()
End Sub
Private Sub SetDimensions(ByVal width As Int32, ByVal height As Int32)
If width <;= 0 Then
Throw New ArgumentOutOfRangeException(“width”, width, “Argument out of range, must be greater than zero.”)
End If
If (height <;= 0) Then
Throw New ArgumentOutOfRangeException(“height”, height, “Argument out of range, must be greater than zero.”)
End If
me.m_width = width
me.m_height = height
End Sub
Private Sub SetFamilyName(ByVal familyName As String)
Try
Dim font As Font = New Font(familyName, 12.0F)
me.m_familyName = familyName
font.Dispose()
Catch ex As Exception
Me.m_familyName = System.Drawing.FontFamily.GenericSerif.Name
end try
End Sub
Private Sub GenerateImage()
Dim bitmap As New Bitmap(Me.m_width, Me.m_height, PixelFormat.Format32bppArgb)
‘Create graphic object
Dim g As Graphics = Graphics.FromImage(bitmap)
g.SmoothingMode = SmoothingMode.AntiAlias
Dim rect As New RectangleF(0, 0, Me.m_width, Me.m_height)
‘Fill the background
Dim hatchBrush As New HatchBrush(HatchStyle.SmallConfetti, Color.LightGray, Color.White)
g.FillRectangle(hatchBrush, rect)
‘Set the source
Dim size As SizeF
Dim fontSize As Single = rect.Height + 1
Dim font As Font
‘Set the font size
Do
fontSize = fontSize – 1
font = NewFont(Me.m_familyName, fontSize, FontStyle.Bold)
size = g.MeasureString(Me.m_text, font)
Loop While(size.Width >; rect.Width)
‘Set the text format
Dim format As New StringFormat
format.Alignment = StringAlignment.Center
format.LineAlignment = StringAlignment.Center
Dim path As New GraphicsPath
path.AddString(Me.m_text, font.FontFamily, CType(font.Style, Int32), font.Size, rect, format)
Dim v As Single = 4.0F
Dim points As System.Drawing.PointF() = { _
New System.Drawing.PointF(m_random.Next(CType(rect.Width, Integer)) / v, m_random.Next(CType(rect.Height, Integer)) / v), _
New System.Drawing.PointF(rect.Width – m_random.Next(CType(rect.Width, Integer)) / v, m_random.Next(CType(rect.Height, Integer)) / v), _
New System.Drawing.PointF(m_random.Next(CType(rect.Width, Integer)) / v, rect.Height – m_random.Next(CType(rect.Height, Integer)) / v), _
New System.Drawing.PointF(rect.Width – m_random.Next(CType(rect.Width, Integer)) / v, rect.Height – m_random.Next(CType(rect.Height, Integer)) / v)}
Dim matrix As New Matrix
matrix.Translate(1, 3)
‘We distort the image
path.Warp(points, rect, matrix, 0)
‘draw the text
hatchBrush = New HatchBrush(HatchStyle.OutlinedDiamond, Color.Orange, Color.BlueViolet)
g.FillPath(hatchBrush, path)
‘Add effects
Dim m As Int32 = Math.Max(CType(rect.Width, Integer), CType(rect.Height, Integer))
Dim i As Int32 = 0
While i <; CType((rect.Width * rect.Height / 30.0F), Int32)
Dim x As Int32 = m_random.Next(CType(rect.Width, Integer))
Dim and As Int32 = m_random.Next(CType(rect.Height, Integer))
Dim w As Int32 = m_random.Next(CType(m / 50, Integer))
Dim h As Int32 = m_random.Next(CType(m / 50, Integer))
g.FillEllipse(hatchBrush, x, y, w, h)
i = i + 1
End While
font.Dispose()
hatchBrush.Dispose()
g.Dispose()
‘set the image
me.m_image = bitmap
End Sub
end class
Now in the project we will create the page that points to our image (the first control that we have added in the project, and in the Page_Load we will put this code:
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
‘We create an image by creating the text saved in the session
Dim ab As New ImageAntiBots(Session(“AntiBots”).ToString(), 200, 50, “Arial”)
‘We change the response to the client to type “image/jpeg”
Me.Response.Clear()
Me.Response.ContentType = “image/jpeg”
‘Save the image in the Response
ab.Image.Save(Me.Response.OutputStream, ImageFormat.Jpeg)
End Sub
And finally, in the registration form, where we have added the controls, in the submit button, use this condition:
If bAntiBots Then
‘ Create the record
else
‘ The security code is not set correctly
end if
You can download all the source code by clicking
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