Q:

how to secure a app to make a closed beta in android?

i need to know how can i secure my app to make a close beta?
i want to send my app to some people so that they can test it. but i dont want them to share the .apk with other people and just use it some days. so i need to implement some kind of trial/beta mode.
i need something, that the app e.g. only runs 7 days or so. how to do this?

A:

There are a few ways to ensure security:

Get a server, and have a server side authentication based on a unique device ID, like an IMEI or MAC address. Any device which does not belong to your testers will not be listed on your server, and you can stop the app from running.
If possible, have each person come to you and install the apk yourself, instead of mailing it to them
Create a trial system. Store the date on which the person first accessed your app from the device, and stop letting him use it n days later. If you store this on a server along with the unique ID, it'll be safer, as if it is stored in the shared preferences or something, the user could get around it by clearing the data or uninstalling and reinstalling the app.
Obfuscate your code using a tool like ProGuard. This will add an extra layer of security incase someone decompiles your app

Note that these are only a few suggestions, and none of them are 100% secure. AFAIK, there is no way to ensure 100% security, short having having the devices locked in a lead room, and letting in the testers one at a time. And there is a way to get around that too, I bet.

