How to prevent application thievery (specific to Android applications)?

There is a single, useful connection between an application buyer and the developer through the marketplace, the forwarding email address provided by google to contact the buyer.

Utilizing the integration callback setting to send buy information to your own server, you can use PHP to send a unique identifier (registration code) to the buy via email (real time as the callback is shipped from google during a purchase. The user then uses this email to register their software using the unique identifier that is then linked to their android ID (or google account username) and the software is "activated" and guaranteed to be legitimate.

Obvious Questions

• Why is this a suitable solution when it requires the user to read email? Our market are those people who are capable of buying an application using an android device. By using an android device, it is implied that the user has a google account which implies they know how to use email.

• How do I use the email with the unique identifier with my application? Create a content handler in your application that handles something like "myactivator://uniqueid-or-something" which causes your application to communicate to your internal server that keeps tabs on activations. Embed this as a link in the email that the user can click on.

• How should I generate the unique identifer? I'm going to use the email somehow - I'm fairly confident google has already made it unique enough to disallow any feasible method of contact information selling.

• What about people who have already purchased the software? A lot of options here - none ideal or terrible.

  • Send emails to all previous buyers
  • Allow users to activate by typing in their order number (can be obtained by logging into checkout.google.com.

Why bother?

Because some of us put a lot of time into applications and saying "you should just accept pirating" is a slap in the face.

Now there is the new Google App Licensing available. For deeper information read about it in the android developer blog.

A short summary: Google provides a library that makes a inter process call to the market client on the phone. The market client will then ask the google servers if the signed in user has purchased the app and forward this answer to you. There should be a public key in you developer profile that you need to encrypt the connection to the google server to prevent spoofing of answers. You also provide a application and device unique id with the query to make it impossible to forward approved queries to another device and build something like an licensing proxy with one bought copy forwarding the IS LICENSED answers to other devices.

At the moment this service looks secure enough to protect even the more valuable apps in the market. I will give it a try and maybe come back and leave some more informations after I used it a little bit.

If your app is really popular like an EA game or something this wan't stop users from hacking it. To hack the app somebody has to buy it, then unzip the apk, and edit the bytecode of your app to think that the market send a correct answer. The new byte code can be packed into another apk and can be installed on every phone that allows side loading. To make this harder you can always try to obfuscate your apk and make your bytecode hard to understand.