.Net Coding Challenge #5

[iCrack]

Here's my submission then...

Spoiler (Click to View)

Module1 - Generate Captcha

Code:

Imports System
Imports System.Security.Cryptography
Module Module1
    Public Class RandomCAPTCHA
        Private Shared DEFAULT_MIN_CAPTCHA_LENGTH As Integer = 1
        Private Shared DEFAULT_MAX_CAPTCHA_LENGTH As Integer = 1
        Private Shared CAPTCHA_CHARS_UCASE As String = "ABCDEFGHJKLMNPQRSTWXYZ"
        Private Shared CAPTCHA_CHARS_LCASE As String = "abcdefgijkmnopqrstwxyz"
        Private Shared CAPTCHA_CHARS_NUMERIC As String = "123456789"
        Private Shared CAPTCHA_CHARS_SPECIAL As String = "*$-+?_&=!%{}/"
        Public Shared Function Generate() As String
            Generate = Generate(DEFAULT_MIN_CAPTCHA_LENGTH, DEFAULT_MAX_CAPTCHA_LENGTH)
        End Function
        Public Shared Function Generate(ByVal length As Integer) As String
            Generate = Generate(length, length)
        End Function
        Public Shared Function Generate(ByVal minLength As Integer, ByVal maxLength As Integer) As String
            If (minLength <= 0 Or maxLength <= 0 Or minLength > maxLength) Then
                Generate = Nothing
            End If
            Dim charGroups As Char()() = New Char()() {CAPTCHA_CHARS_LCASE.ToCharArray(), CAPTCHA_CHARS_UCASE.ToCharArray(), CAPTCHA_CHARS_NUMERIC.ToCharArray(), CAPTCHA_CHARS_SPECIAL.ToCharArray()}
            Dim charsLeftInGroup As Integer() = New Integer(charGroups.Length - 1) {}
            Dim I As Integer
            For I = 0 To charsLeftInGroup.Length - 1
                charsLeftInGroup(I) = charGroups(I).Length
            Next
            Dim leftGroupsOrder As Integer() = New Integer(charGroups.Length - 1) {}
            For I = 0 To leftGroupsOrder.Length - 1
                leftGroupsOrder(I) = I
            Next
            Dim randomBytes As Byte() = New Byte(3) {}
            Dim rng As RNGCryptoServiceProvider = New RNGCryptoServiceProvider()
            rng.GetBytes(randomBytes)
            Dim seed As Integer = ((randomBytes(0) And &H7F) << 24 Or randomBytes(1) << 16 Or randomBytes(2) << 8 Or randomBytes(3))
            Dim random As Random = New Random(seed)
            Dim CAPTCHA As Char() = Nothing
            If (minLength < maxLength) Then
                CAPTCHA = New Char(random.Next(minLength - 1, maxLength)) {}
            Else
                CAPTCHA = New Char(minLength - 1) {}
            End If
            Dim nextCharIdx As Integer
            Dim nextGroupIdx As Integer
            Dim nextLeftGroupsOrderIdx As Integer
            Dim lastCharIdx As Integer
            Dim lastLeftGroupsOrderIdx As Integer = leftGroupsOrder.Length - 1
            For I = 0 To CAPTCHA.Length - 1
                If (lastLeftGroupsOrderIdx = 0) Then
                    nextLeftGroupsOrderIdx = 0
                Else
                    nextLeftGroupsOrderIdx = random.Next(0, lastLeftGroupsOrderIdx)
                End If
                nextGroupIdx = leftGroupsOrder(nextLeftGroupsOrderIdx)
                lastCharIdx = charsLeftInGroup(nextGroupIdx) - 1
                If (lastCharIdx = 0) Then
                    nextCharIdx = 0
                Else
                    nextCharIdx = random.Next(0, lastCharIdx + 1)
                End If
                CAPTCHA(I) = charGroups(nextGroupIdx)(nextCharIdx)
                If (lastCharIdx = 0) Then
                    charsLeftInGroup(nextGroupIdx) = _
                                    charGroups(nextGroupIdx).Length
                Else
                    If (lastCharIdx <> nextCharIdx) Then
                        Dim temp As Char = charGroups(nextGroupIdx)(lastCharIdx)
                        charGroups(nextGroupIdx)(lastCharIdx) = _
                                    charGroups(nextGroupIdx)(nextCharIdx)
                        charGroups(nextGroupIdx)(nextCharIdx) = temp
                    End If
                    charsLeftInGroup(nextGroupIdx) = _
                               charsLeftInGroup(nextGroupIdx) - 1
                End If
                If (lastLeftGroupsOrderIdx = 0) Then
                    lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1
                Else
                    If (lastLeftGroupsOrderIdx <> nextLeftGroupsOrderIdx) Then
                        Dim temp As Integer = _
                                    leftGroupsOrder(lastLeftGroupsOrderIdx)
                        leftGroupsOrder(lastLeftGroupsOrderIdx) = _
                                    leftGroupsOrder(nextLeftGroupsOrderIdx)
                        leftGroupsOrder(nextLeftGroupsOrderIdx) = temp
                    End If
                    lastLeftGroupsOrderIdx = lastLeftGroupsOrderIdx - 1
                End If
            Next
            Generate = New String(CAPTCHA)
        End Function
    End Class
    Sub Main()
        Dim I As Integer
        For I = 1 To 1
            Form1.Label1.Text = RandomCAPTCHA.Generate(1)
            Form1.Label2.Text = RandomCAPTCHA.Generate(1)
            Form1.Label3.Text = RandomCAPTCHA.Generate(1)
            Form1.Label4.Text = RandomCAPTCHA.Generate(1)
            Form1.Label5.Text = RandomCAPTCHA.Generate(1)
            Form1.Label6.Text = RandomCAPTCHA.Generate(1)
        Next
    End Sub
End Module

Form1 - Captcha Verification

Code:

Public Class Form1
    Private Sub Generate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Generate.Click
        Call Main()
        Verification.Clear()
    End Sub
    Private Sub Test_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Test.Click
        Dim aa = Label1.Text
        Dim bb = Label2.Text
        Dim cc = Label3.Text
        Dim dd = Label4.Text
        Dim ee = Label5.Text
        Dim ff = Label6.Text
        If Verification.Text = aa + bb + cc + dd + ee + ff Then
            MsgBox("You did it!")
        Else
            MsgBox("Nop!")
        End If
    End Sub
End Class

Download .EXE: http://localhostr.com/file/6O0KRds/Captcha.exe