Generate a Random String Key in VB.NET

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Introduction

I had to create a piece of code that will give me a set of randomly generated keys. Each key had to consist of letters and numbers, and the letters could be either (randomly) lowercase or uppercase.

Looking at some sample code on the web, I could not find what I needed. All the examples I found either generated numbers only, or letters only. I also wanted this random key to be based on a certain rule that made it "not straightforward" random, so, I came up with this little piece of code.

Using the code

The way it works is as follows:

You feed it with a string of letters: KeyLetters, a string of numbers: KeyNumbers, and how many characters you want the random key to be: Keychars. We then call Generate() which goes and generates a random number through the Randomize() statement and the Rnd() function.

Multiply Rnd() by 111 -could be any number we choose which is sufficient enough to bring the value above zero. If the resulting number is an even number, then our random character will be a letter. If we get an odd number, then our random character will be a number. To generate a random character, we generate a random index for one of the character arrays (depending on what our random character will be). Once we have an index which is >= o, we use it to get the value in the corresponding index in the character array.

If we are generating a number, then that is our random character. If we are generating a letter, then we need to determine whether we want it uppercase or lowercase. For that purpose we generate another random number by multiplying the value of Rnd() by 99 – could be any other number too – and then determine whether the result is even or odd. This time, we capitalize the letter if we get an odd number, otherwise we leave it as it is.

And so on, … the loop keeps "looping" while using, and we use a StringBuilder to construct our resulting string , until we've generated the desired number of characters for our Random Key. We convert the StringBuilder to String and return it with the function.

Note: XML comments in the source code were generated using "VBXC - VB.NET XML Commentor beta 3". I highly recommend it.

Module1.vb

Module Module1
    Sub Main()
        Dim KeyGen As RandomKeyGenerator
        Dim NumKeys As Integer
        Dim i_Keys As Integer
        Dim RandomKey As String

        ''' MODIFY THIS TO GET MORE KEYS    - LAITH - 27/07/2005 22:48:30 -
        NumKeys = 20

        KeyGen = New RandomKeyGenerator
        KeyGen.KeyLetters = "abcdefghijklmnopqrstuvwxyz"
        KeyGen.KeyNumbers = "0123456789"
        KeyGen.KeyChars = 12
        For i_Keys = 1 To NumKeys
            RandomKey = KeyGen.Generate()
            Console.WriteLine(RandomKey)
        Next
        Console.WriteLine("Press any key to exit...")
        Console.Read()
    End Sub
End Module

RandomKeyGenerator.vb

Option Strict On
Imports System.Text
''' <date>27072005</date><time>070339</time>
''' <type>class</type>
''' <summary>
''' REQUIRES PROPERTIES: KeyLetters, KeyNumbers, MaxChars
''' </summary>
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()

    ''' <date>27072005</date><time>071924</time>
    ''' <type>property</type>
    ''' <summary>
    ''' WRITE ONLY PROPERTY. HAS TO BE SET BEFORE CALLING GENERATE()
    ''' </summary>
    Protected Friend WriteOnly Property KeyLetters() As String
        Set(ByVal Value As String)
            Key_Letters = Value
        End Set
    End Property

    ''' <date>27072005</date><time>071924</time>
    ''' <type>property</type>
    ''' <summary>
    ''' WRITE ONLY PROPERTY. HAS TO BE SET BEFORE CALLING GENERATE()
    ''' </summary>
    Protected Friend WriteOnly Property KeyNumbers() As String
        Set(ByVal Value As String)
            Key_Numbers = Value
        End Set
    End Property

    ''' <date>27072005</date><time>071924</time>
    ''' <type>property</type>
    ''' <summary>
    ''' WRITE ONLY PROPERTY. HAS TO BE SET BEFORE CALLING GENERATE()
    ''' </summary>
    Protected Friend WriteOnly Property KeyChars() As Integer
        Set(ByVal Value As Integer)
            Key_Chars = Value
        End Set
    End Property

    ''' <date>27072005</date><time>072344</time>
    ''' <type>function</type>
    ''' <summary>
    ''' GENERATES A RANDOM STRING OF LETTERS AND NUMBERS.
    ''' LETTERS CAN BE RANDOMLY CAPITAL OR SMALL.
    ''' </summary>
    ''' <returns type="String">RETURNS THE
    '''         RANDOMLY GENERATED KEY</returns>
    Function Generate() As String
        Dim i_key As Integer
        Dim Random1 As Single
        Dim arrIndex As Int16
        Dim sb As New StringBuilder
        Dim RandomLetter As String

        ''' CONVERT LettersArray & NumbersArray TO CHARACTR ARRAYS
        LettersArray = Key_Letters.ToCharArray
        NumbersArray = Key_Numbers.ToCharArray

        For i_key = 1 To Key_Chars
            ''' START THE CLOCK    - LAITH - 27/07/2005 18:01:18 -
            Randomize()
            Random1 = Rnd()
            arrIndex = -1
            ''' IF THE VALUE IS AN EVEN NUMBER WE GENERATE A LETTER,
            ''' OTHERWISE WE GENERATE A NUMBER  
            '''          - LAITH - 27/07/2005 18:02:55 -
            ''' THE NUMBER '111' WAS RANDOMLY CHOSEN. ANY NUMBER
            ''' WILL DO, WE JUST NEED TO BRING THE VALUE
            ''' ABOVE '0'     - LAITH - 27/07/2005 18:40:48 -
            If (CType(Random1 * 111, Integer)) Mod 2 = 0 Then
                ''' GENERATE A RANDOM INDEX IN THE LETTERS
                ''' CHARACTER ARRAY   - LAITH - 27/07/2005 18:47:44 -
                Do While arrIndex < 0
                    arrIndex = _
                     Convert.ToInt16(LettersArray.GetUpperBound(0) _
                     * Random1)
                Loop
                RandomLetter = LettersArray(arrIndex)
                ''' CREATE ANOTHER RANDOM NUMBER. IF IT IS ODD,
                ''' WE CAPITALIZE THE LETTER
                '''      - LAITH - 27/07/2005 18:55:59 -
                If (CType(arrIndex * Random1 * 99, Integer)) Mod 2 <> 0 Then
                    RandomLetter = LettersArray(arrIndex).ToString
                    RandomLetter = RandomLetter.ToUpper
                End If
                sb.Append(RandomLetter)
            Else
                ''' GENERATE A RANDOM INDEX IN THE NUMBERS
                ''' CHARACTER ARRAY   - LAITH - 27/07/2005 18:47:44 -
                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