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Idea

Instead of selling your software as a one-time purchase, you can instead collect monthly or yearly payments from your customers.

There are at least three ways to set up a licensing model that supports some form of recurring payments. You can require an active subscription to:

• Use the product (or some of its features)
• Get updates, but allow access to older versions of the product after the expiration date (similar to one-time purchase model)
• Receive support, but still allow access to the product. You can combine this with the “updates constraint” above.

Both of these models depend on the expiration date property that each license key has. We will cover the details of how this is implemented in the next section.

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Implementation

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In the dashboard

The expiration date of a license key can be controlled by clicking on the desired license on the product page. A box will popup, similar to the one below.

By adding a certain amount of days to a license key, Cryptolens will automatically determine the expiration date, in order to ensure that the license key can be used for at least the number of days that was specified or longer (if the user has some days left before expiration).

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In your application

In the introduction, we mentioned three ideas to subscription based licensing model can be used: by constraining access to the entire product, newer versions of it and/or support.

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Require subscription to access the product

This is quite simple to restrict access to entire product if the license key has expired. In the code below, we assume that you have read the key verification tutorial. The only change is to add HasNotExpired() in the if-statement below:

// notice that we have added ".HasNotExpired()".

if (result == null || result.Result == ResultType.Error ||
    !result.LicenseKey.HasValidSignature(RSAPubKey)
           .HasNotExpired().IsValid())
{
    // an error occurred or the key is invalid or it cannot be activated
    // (eg. the limit of activated devices was achieved)
    Console.WriteLine("The license does not work.");
}
else
{
    // everything went fine if we are here!
    Console.WriteLine("The license is valid!");
}

If you use a specific feature to denote time-limited licenses, you can similarly add HasFeature(<feature number>) in the if-statement.

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Require subscription to access updates

In this scenario, instead of restricting access to all versions of the product, we allow users to keep using the latest major version before they stopped paying for updates.

In the image above, we assume major releases (eg. v1.0 and v2.0) are released three times a year. Minor releases (eg. v1.1 and v1.2) are released more frequently. Let us further assume that users pay on a monthly basis.

The idea is as follows: if the user stops extending their subscription before the end of May, they will only be able to use v1.*. If they stop in June, they will be able to use v2.*, and so for.

We can express this in the code below. It assumes you use the code-snippet from the key verification tutorial. The code below is put inside the else-statement.

// ..
// everything went fine if we are here!
Console.WriteLine("The license is valid!");

// we need to add this extra code inside the else-statement

string currentApplicationVersion = "1";

if (license.HasNotExpired().IsValid())
{
     // the SLA is still valid so we proceed as usual
}
else if (license.HasExpired().IsValid())
{
    // if the SLA has expired, we want to check the notes field 
    // to see which version they bought the last time
    if (license.notes >= currentApplicationVersion) 
    {
        // proceed as usual
    }
    else 
    {
        // close the application
    }
}

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Require subscription to receive support

If you plan to only use subscriptions to keep track of who is eligible for support, no additional code is required besides what is presented in the key verification tutorial.

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Integration with other services

The key to get subscriptions up and running is the ExtendLicense method in the Web API. It allows you to extend the expiration date of a license key by a certain number of days. For example, let’s assume the users pays for the subscription on a monthly basis. Once a payment is successful, we can extend the duration of the license by sending a GET request to as shown below (the access token can be created on this page):

https://app.cryptolens.io/api/key/ExtendLicense?ProductId=123&Key=FRQHQ-FSOSD-BWOPU-KJOWF&NoOfDays=30&token=<access token with 'Extend License permission'>

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Tips when integrating with Stripe

If you use subscriptions in Stripe, there are two useful events that you can use to monitor subscriptions (when using Webhooks):

• invoice.payment_succeeded - when this event is received, ExtendLicense method should be called for the license that the subscription belongs to.
• customer.subscription.deleted - when this event is received, BlockKey should be called to make sure the license key can no longer be used.

An implementation that supports recurring payments will be released in the coming weeks. In meantime, please reach out to us should you have any questions!