Generating serial numbers and keys in C# and VB.NET

Using serial numbers is the most common way to unlock applications in the market today. Microsoft made that part of our life (us developers and isv) easier using serial keys all over their product lines. This has made final users and customer familiar with the term and how the should use them to activate their applications and that’s why we use them in our .net licensing product LicenseSpot.

One aspect to keep in mind about generating serial numbers is to keep them unique. In the function below we’re using GUIDs to generate serial numbers as we know for sure that they’re unique.

The function basically takes a guid string and just take the desired length for the key. It returns a serial number with the format: XXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXX.

public  string GetSerialNumber()
	Guid serialGuid = Guid.NewGuid();
	string uniqueSerial = serialGuid.ToString("N");

	string uniqueSerialLength = uniqueSerial.Substring(0, 28).ToUpper();

	char[] serialArray = uniqueSerialLength.ToCharArray();
	string finalSerialNumber = "";

	int j= 0;
	for (int i = 0; i < 28; i++)
		for (j = i; j < 4 + i; j++)
			finalSerialNumber += serialArray[j];
		if (j == 28)
			i = (j) - 1;
			finalSerialNumber += "-";

	return finalSerialNumber;

Below the VB.NET code:

Public Function GetSerialNumber() As String
	Dim serialGuid As Guid = Guid.NewGuid()
	Dim uniqueSerial As String = serialGuid.ToString("N")
	Dim uniqueSerialLength As String = uniqueSerial.Substring(0, 28).ToUpper()

	Dim serialArray As Char() = uniqueSerialLength.ToCharArray()
	Dim finalSerialNumber As String = ""

	Dim j As Integer = 0
	For i As Integer = 0 To 27
		For j = i To 4 + (i - 1)
			finalSerialNumber += serialArray(j)
		If j = 28 Then
			Exit For
			i = (j) - 1
			finalSerialNumber += "-"
		End If

	Return finalSerialNumber
End Function