Imports Microsoft.VisualBasic
Imports System.Text

Public Class RandomKeyGenerator
    Dim Key_Letters As String
    Dim Key_Numbers As String
    Dim Key_Chars As Integer
    Dim LettersArray As Char()
    Dim NumbersArray As Char()

    ' Generate random alphanumeric string 
    Function Generate(ByVal KeyLetters As String, ByVal KeyNumbers As String, ByVal KeyChars As Integer) As String
        Dim i_key As Integer
        Dim Random1 As Single
        Dim arrIndex As Int16
        Dim sb As New StringBuilder
        Dim RandomLetter As String

        LettersArray = KeyLetters.ToCharArray()
        NumbersArray = KeyNumbers.ToCharArray()

        For i_key = 1 To KeyChars
            Randomize()
            Random1 = Rnd()
            arrIndex = -1
            If (CType(Random1 * 111, Integer)) Mod 2 = 0 Then
                Do While arrIndex < 0
                    arrIndex = _
                     Convert.ToInt16(LettersArray.GetUpperBound(0) _
                     * Random1)
                Loop
                RandomLetter = LettersArray(arrIndex)
                If (CType(arrIndex * Random1 * 99, Integer)) Mod 2 <> 0 Then
                    RandomLetter = LettersArray(arrIndex).ToString
                    RandomLetter = RandomLetter.ToUpper
                End If
                sb.Append(RandomLetter)
            Else
                Do While arrIndex < 0
                    arrIndex = _
                      Convert.ToInt16(NumbersArray.GetUpperBound(0) _
                      * Random1)
                Loop
                sb.Append(NumbersArray(arrIndex))
            End If
        Next
        Return sb.ToString
    End Function

End Class