Soraco Technologies

Posted on Feb 19

Basic License Validation in .NET: 10 Lines to Protect Your Application

#dotnet #csharp #licensing #security

Your .NET application needs license protection. Here's the simplest way to add it — 10 lines of code.

The Problem

You built a great app. Now you want to:

Stop unauthorized copies
Issue trial licenses
Track activations
Manage subscriptions

Solution: Add license validation at startup.

The Code

using QLM.LicenseLib;

static void Main(string[] args)
{
    var lv = new LicenseValidator("settings.xml");

    bool needsActivation = false;
    string errorMsg = string.Empty;

    bool isValid = lv.ValidateLicenseAtStartup(
        ELicenseBinding.ComputerName,
        ref needsActivation,
        ref errorMsg
    );

    if (!isValid || needsActivation)
    {
        Console.WriteLine("License invalid: " + errorMsg);
        return;
    }

    // Your app code here
    Console.WriteLine("License valid - running app");
}

That's it. 10 lines.

How It Works

ValidateLicenseAtStartup does 5 things:

Looks for a license stored locally
Validates the signature (RSA-2048 encryption)
Checks expiry date (for trials/subscriptions)
Validates online (optional server check)
Returns true/false

If no license exists, needsActivation is set to true.

Hardware Binding Options

Tie licenses to specific computers:

ELicenseBinding.ComputerName          // Computer name
ELicenseBinding.MacAddress            // MAC address
ELicenseBinding.MotherboardSerialNumber  // Motherboard
ELicenseBinding.HardDiskSerialNumber     // Hard drive

Most common: ComputerName (easy for users, good enough security)

Most secure: MotherboardSerialNumber (survives OS reinstalls)

What About the License Wizard?

You'll want a UI for activation. QLM includes one:

if (!isValid || needsActivation)
{
    // Launch QLM License Wizard
    System.Diagnostics.Process.Start("QlmLicenseWizard.exe", 
        "/settings \"settings.xml\"");

    // Re-validate after activation
    isValid = lv.ValidateLicenseAtStartup(
        ELicenseBinding.ComputerName,
        ref needsActivation,
        ref errorMsg
    );
}

The wizard handles:

Online activation
Offline activation
Trial key entry
Purchase links

Real Example: Console App

using System;
using QLM.LicenseLib;

class Program
{
    static LicenseValidator lv;
    static string settingsFile = "Demo 1.0.lw.xml";

    static void Main(string[] args)
    {
        if (ValidateLicense())
        {
            RunApp();
        }
        else
        {
            Console.WriteLine("Press any key to exit...");
            Console.ReadKey();
        }
    }

    static bool ValidateLicense()
    {
        lv = new LicenseValidator(settingsFile);

        bool needsActivation = false;
        string errorMsg = string.Empty;

        bool isValid = lv.ValidateLicenseAtStartup(
            ELicenseBinding.ComputerName,
            ref needsActivation,
            ref errorMsg
        );

        if (!isValid || needsActivation)
        {
            Console.WriteLine("License validation failed: " + errorMsg);
            Console.WriteLine("Please activate your license.");
            return false;
        }

        return true;
    }

    static void RunApp()
    {
        Console.WriteLine("License valid!");
        Console.WriteLine("Running application...");
        // Your app logic here
    }
}

Supported Platforms

Windows: .NET Framework 2.x / 4.x, .NET 6/7/8/9/10
Cross-platform: .NET 6/7/8/9/10 (macOS, Linux)
Mobile: Android, iOS (.NET MAUI, Xamarin)

Quick License Manager

This uses Quick License Manager (QLM) — the most complete .NET licensing solution.

Pricing (per developer):

QLM Express: $200/year
QLM Professional: $699/year
QLM Enterprise: $999/year

Features:

RSA-2048 + AES-256 encryption
Online & offline activation
12 e-commerce integrations
Trial & subscription support
Floating licenses (Enterprise)
Customer self-service portal

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