.Net Coding Challenge #5

[KoBE]

My Submission (No Labels )+Comments (Click to View)

This could very easily be expanded on to make a decent Captcha verifier class. I whipped this up before bed so I didn't put any effort into a GUI. I mainly wanted to show a different way to do this rather then generating a Label.

Enjoy.

Code:

Imports System.Drawing
Imports System.Security.Cryptography
Public Class Form1
    Dim x As String     'used to store the text before painting, then stores the MD5 of what was painted
    Private Sub btnGenerate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGenerate.Click
        'new bitmap to draw the captcha
        Dim xBitmap As New Bitmap(200, 50)
        'new brush to paint with
        Dim xBrush As New SolidBrush(Color.Black)
        'font used to draw captcha
        Dim xFont As New Font(FontFamily.GenericSansSerif, 20)
        'create a new graphic from the bitmat we created
        Dim gfx As Graphics = Graphics.FromImage(xBitmap)
        'return an 8 character string
        x = NewRand()
        'draw our string to the graphic
        gfx.DrawString(x, xFont, xBrush, 0, 0)
        'set the picture box image to our captcha
        pbCap.Image = xBitmap
        'md5 our captcha so incase stolen(via windows handle)
        x = TxtHash(x)
    End Sub
    Private Sub btnCheck_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCheck.Click
        'hash the answer and verify against the hashed captcha
        If TxtHash(txtAnswer.Text) = x Then
            MessageBox.Show("Sweet balls you got it!")
        Else
            MessageBox.Show("Uh oh, you suck.")
        End If
    End Sub

    Private Function NewRand()
        'characters allowed in the captcha
        Dim strText As String = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"
        'new random number generator()
        Dim rand As New Random
        'holds our random character string
        Dim xString As String = ""
        For i As Integer = 0 To 8
            'loops 8 times, getting a random character from our allowed characters
            xString += strText.Substring(rand.Next(strText.Length - 1), 1)
        Next
        'return the result
        Return xString
    End Function
    Private Function TxtHash(ByVal str As String)
        'new md5 class
        Dim hash As MD5 = MD5.Create()
        'md5 hash in byte form
        Dim bytes As Byte() = hash.ComputeHash(System.Text.Encoding.ASCII.GetBytes(str))
        'return the md5 as a string
        Return BitConverter.ToString(bytes).Replace("-", "")
    End Function

End Class