I recently wrote a relatively simple program that imitates your standard installer program. There are four screens to it: the first one, where you have to enter the "CD Code", which is verified in a way that makes it very difficult to deduct, from the code, what the code is. The next window just displays a "Serial Number". The next one asks you what file you want to "modify", either by typing in the path, or by click on the "browse" button. The last part just has two progress bars that "fill up" at a random speed; the upper one moves at 1/100 of the speed of the other.

The part that is of most interest is the first one. the following is the code:

Private Sub Command1_Click()

Dim check As Variant
Dim checks As String
Dim fh As Integer
Dim countercheck As String
Dim filetext As String

On Error GoTo eh

fh = FreeFile

Open "C:\CDtest1.txt" For Input As #fh

Input #fh, filetext

Close #fh

Dim passer As Variant

For passer = 1 To Int(Len(filetext) / 5)
    countercheck = countercheck & Int(Mid(filetext, (passer * 5) - 4, 2) - Asc(Mid(Text1.Text, Int(passer Mod Int(Len(Text1.Text) - 1) + 1), 1)))
Next

For check = 1 To 26
    If IsNumeric(Mid(Text1.Text, check, 1)) = False Then
        checks = checks & Asc(Mid(Text1.Text, check, 1))
    Else
        checks = checks & Mid(Text1.Text, check, 1)
    End If
Next

If checks = filetext Then
    Frame1.Visible = False
    Frame2.Visible = True
Else
    MsgBox "Incorrect code"
    Text1.Text = ""
    Command1.Enabled = False
End If

Exit Sub

eh:

MsgBox "Problem: " & Err.Description
Close #fh

End Sub

There is no longer a single key that will pass the test. Now, you need another program will both generate a key for you, and write an encrypted file containing the info that the above code needs in order to verify what you type in.
In case you were wondering, the frames are what I used to have multiple "screens". I simply superimposed them all.

Last edited by Laterally Speaking (2007-08-01 01:34:33)