Protecting Your Software Using Simple Serial Number/Activation Key Pair

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Introduction

In this simple article, I am going to show how you can protect your software from unauthorized copying by creating a serial number/activation key pair based on the physical address (MAC) of the network adapter on the client's machine.

Getting the MAC Address and Generating the Serial Number

The first step is to get the MAC address of the client's machine. This could be achieved by using the ManagementClass class located in the System.Management assembly. We have to add a reference to that assembly to our project, and import it into SecurityManager.vb, which will be the class in which we place the GetSerial() and CheckKey() functions. These two functions will be responsible for generating the serial number from the MAC address and checking whether the key entered by the user is valid. As a first step, we define the GetSerial() function as follows:

Public Function GetSerial() As Long
    Dim mc As New ManagementClass("Win32_NetworkAdapterConfiguration")
    Dim mac As String = ""
    'Getting network adapters collection
    Dim moc As ManagementObjectCollection = mc.GetInstances

    'Here we iterate over available network adapters, 
    'picking the first possible one
    For Each mo As ManagementObject In moc
        If mo.Item("IPEnabled") Then
            mac = mo.Item("MacAddress").ToString
            Exit For
        End If
    Next

    mc.Dispose()

    'This is a simple function that we use to get a serial out
    'of our MAC address. Say that x is the MAC and y is the serial,
    'the function would be y += x[i] + (i * 2) where i is the index
    'of MAC address element.
    Dim sum As Long = 0
    Dim index As Integer = 1
    For Each ch As Char In mac
        If Char.IsDigit(ch) Then
            sum += sum + Integer.Parse(ch) * (index * 2)
        ElseIf Char.IsLetter(ch) Then
            Select Case ch.ToString.ToUpper
                Case "A"
                    sum += sum + 10 * (index * 2)
                Case "B"
                    sum += sum + 11 * (index * 2)
                Case "C"
                    sum += sum + 12 * (index * 2)
                Case "D"
                    sum += sum + 13 * (index * 2)
                Case "E"
                    sum += sum + 14 * (index * 2)
                Case "F"
                    sum += sum + 15 * (index * 2)
            End Select
        End If

        index += 1
    Next

    Return sum
End Function

This function will give us the unique serial number of each MAC address (not totally unique, but similar to hash function uniqueness).

Generating Activation Key from the Serial Number

The second step is to create the key generator which will generate the activation key from a given serial number. This generator will be placed in a class called KeyGenerator. This class will contain a function which will apply a simple mathematical function on the serial number to get the activation key. In this case, I will use the function f(x) = x² + 53/x + 113 * (x/4).

Public Class KeyGenerator
    Public Function GenerateKey(ByVal serial As Long) As Long
        Dim x As Long = serial
        Return x * x + 53 / x + 113 * (x / 4)
    End Function
End Class

Back to SecurityManager.vb, we need to add one more function, which is CheckKey(). This function will take the activation key as a parameter, apply the key-generating function on the current MAC address, then compare the two keys to see whether they match or not.

Public Function CheckKey(ByVal key As Long) As Boolean
    Dim x As Long = GetSerial()
    Dim y As Long = x * x + 53 / x + 113 * (x / 4)
    Return y = key
End Function

One important note left: do not place all of these classes in your client's solution! Remember that the key-generating class is only owned by you.

Now you can use these classes to protect your software. You can also use more complicated functions to ensure more security. The key generator may look like this:

If everything is alright, the user would get the following message.

For more articles, please visit my blog (in Arabic only).

Happy coding!