.NET desktop application

This is an old tutorial that we have kept that shows how you can implement basic license verification in a .NET application. We recommend to review our Getting Started Guide and refer to our key verification tutorial for production ready examples.

Our aim of this tutorial is to guide you through, step by step, the process of implementing Cryptolens into your application. We’ll assume that you’ve developed a .NET application and use Visual Studio 2013. If you are using a different language, we recommend to check out this page.

If you want to jump straight into the code, please check out the key verification tutorial.

Our application will have three features (voice, audio and converter), and the ability to license these as a ‘subscription’ (time-limited) or ‘perpetual’ (unlimited time). We will check the license key when we have an Internet connection. If we’re offline, we will use the saved license file. The user will be able to use the software 90 days offline at most.

Cryptolens .NET Client

Now we can start using all of the power of the Cryptolens Client API.

The easiest way to get Cryptolens Client API is through NuGet in Visual Studio.

Go to the solution explorer and right click on the project (not the solution).
Click on Manage NuGet Packages...

Now, type Cryptolens.Licensing into the Browse tab, select SKM Client API and install it.

Adding Code

We almost have all the pieces in place to get a working licensing solution. We will cover the code in this section and look at how to retrieve access tokens and public key (RSA) later.

Our application will have two places where we will need to insert the code:

During license key registration - the first time the user inserts a license key
During application start - to check for existing license on launch

You can download the source code here.

Note, you can find more detailed examples of .NET here and other environments here. Please don’t hesitate to contact us should you have any questions.

License Key Registration

' The code below is based on https://help.cryptolens.io/examples/key-verification.

Dim token = "{access token with permission to access the activate method}"
Dim RSAPubKey = "{Your RSA Public key}"
Dim keyStr = TextBox1.Text.Replace(" ", "")

Dim result = Key.Activate(token:=token, parameters:=New ActivateModel() With {
                  .Key = keyStr,
                  .ProductId = 3349,
                  .Sign = True,
                  .MachineCode = Helpers.GetMachineCode()
                  })

If result Is Nothing OrElse result.Result = ResultType.[Error] OrElse
    Not result.LicenseKey.HasValidSignature(RSAPubKey).IsValid Then
    ' an error occurred or the key is invalid or it cannot be activated
    ' (eg. the limit of activated devices was achieved)
    MsgBox("Unable to access the license server or the key is wrong.")

Else
    ' everything went fine if we are here!

    Dim license = result.LicenseKey

    Form1.Button1.Enabled = license.HasFeature(1).IsValid() ' either we have feature1 or not.
    Form1.Button2.Enabled = license.HasFeature(2).IsValid() ' either we have feature2 or not.
    Form1.Button4.Enabled = license.HasFeature(3).IsValid() ' either we have feature3 or not.

    Form1.Text = "Digital Tools"

    If license.HasFeature(4).HasNotExpired().IsValid() Then
        ' feature 1 is a time limited, so we check that it has not expired.
        Form1.Text = "Digital Tools - " + license.DaysLeft().ToString() + " day(s) left"
    ElseIf license.HasNotFeature(4).IsValid() Then

    Else
        MsgBox("Your license has expired and cannot be used.")
        nolicense()

    End If

    license.SaveToFile()

End If

This code will retrieve all the license data (using Refresh) and enable buttons depending on the features in the license. Features 3-5 indicate a certain functionality whereas Feature 1 is used to indicate a time-limit (in case it’s a subscription). Once we have a valid license, we will save it locally (it will be signed by SKM, because sign is set to true in Refresh).

Application Start

 NoLicense()

' The code below is based on https://help.cryptolens.io/examples/key-verification.

Dim license = New LicenseKey().LoadFromFile()
Dim publicKey = "{Your RSA Public key}"
Dim token = "{access token with permission to access the activate method}"

If license IsNot Nothing Then

    Dim result = Key.Activate(token:=token, parameters:=New ActivateModel() With {
                  .Key = license.Key,
                  .ProductId = 3349,
                  .Sign = True,
                  .MachineCode = Helpers.GetMachineCode()
                  })

    ' either we get a fresh copy of the license or we use the existing one (given it is no more than 90 days old)
    If (result.Result <> ResultType.Error And result.LicenseKey.HasValidSignature(publicKey).IsValid) Or license.HasValidSignature(publicKey, 90).IsValid() Then

        Button1.Enabled = license.HasFeature(1).IsValid() ' either we have feature1 or not.
        Button2.Enabled = license.HasFeature(2).IsValid() ' either we have feature2 or not.
        Button4.Enabled = license.HasFeature(3).IsValid() ' either we have feature3 or not.

        Text = "Digital Tools"

        If license.HasFeature(4).HasNotExpired().IsValid() Then
            ' feature 1 is a time limited, so we check that it has not expired.
            Text = "Digital Tools - " + license.DaysLeft().ToString() + " day(s) left"
        ElseIf license.HasNotFeature(4).IsValid() Then
            ' not time limited.

        Else
            MsgBox("Your license has expired and cannot be used.")
            NoLicense()

        End If

        license.SaveToFile()

    Else
        MsgBox("Your license has expired and cannot be used.")
    End If

Else
    ' no license found. you could tell the user to provide a license key.
End If

When your application launches, we will try to get a new version of the license key, in case it has been modified. If we don’t have internet access, we will use the local copy as long as 90 days have not passed since it was retrieved. Everything else is the same as when the user registers the license for the first time.

Access Tokens

In all of the code examples, you will see variables such as token or auth. They refer to an access token.

The idea behind access tokens is to allow you to:

identify yourself with Cryptolens (authentication) - let Cryptolens know that you are you
make sure only desired permission is given to something (authorization) - eg. method scope, product, etc.

Using an access token, you can specify the methods you want to be able to call, the product you want to use, the license key, and optionally feature you want to change. You can read more about them here.

Creating a new Access Token

In order to create an access token with the permission required by the previous example:

Go to ‘Your account name’ (right corner) > ‘Access Token’.
Click on ‘Create new Access Token’. You will now be on this page.
Enter a name, such as “ActivateToken”.
Check the ‘Activate’ box (under LicenseKey)
Select the ‘Product Lock’ to be the name of your application.
Press ‘Create an Access Token’.
Copy the access token and replace our token with yours.

Example

Public Key

In many cases, you will store license key data locally on your customers’ device, partly to allow your customers to use the application offline. At the same time, you don’t want them to be able to modify the license key data (for example, the number of features they are entitled to and expiration date).

Therefore, Cryptolens will sign the license key (if you explicitly tell it to do so) with your private key. The public key will allow your application to check that the license key file hasn’t been modified since it was by Cryptolens.

The public key won’t allow them to re-sign the data, only to validate it.

Finding your Public Key

In order to find your unique public key:

In the menu in the right corner (with your name), select ‘Security Settings’.
Copy the entire public key and replace it with yours (in the publicKey variable).

Create a Key

We’re now ready to test the code using your account.

Select the product from the list.
Click on ‘Create a new Key’.
Check features 3,4,5.
Optionally, if you want to have a time limit, check feature 1 too.

In case you kept the code as it is (without replacing the token and pubkey with yours), you can test the following:

IWXAZ-FVMOD-KBZQU-DKUFW - all features in one years since this tutorial was written
IYVOO-JCWXQ-LCRBI-ZAIQZ - all features but the recorder with no time constraint.

Done!

You have successfully completed this tutorial! If you would have any questions, please get in touch us with us using chatbox available on each page.

Good luck!

Next steps

You’ve now implemented Cryptolens into your application. Here’s what’s next:

Get Started

Licensing models

Examples

Payments

Features

Security

Cryptolens .NET Client

Adding Code

License Key Registration

Application Start

Access Tokens

Creating a new Access Token

Example

Public Key

Finding your Public Key

Create a Key

Done!

Next steps

Get Started

Licensing models

Examples

Payments

Features

Security

​Cryptolens .NET Client

​Adding Code

​License Key Registration

​Application Start

​Access Tokens

​Creating a new Access Token

​Example

​Public Key

​Finding your Public Key

​Create a Key

​Done!

​Next steps

Cryptolens .NET Client

Adding Code

License Key Registration

Application Start

Access Tokens

Creating a new Access Token

Example

Public Key

Finding your Public Key

Create a Key

Done!

Next steps