How to make the application work through a private key?

Question

Android

How to make the APK file work through a private key, so that it would be impossible to enter it without it and that the key would work for a certain time with the ability to issue a new one? Example: entering the application through a key, it ends in a day and in order to continue using it was necessary to enter a new key

Answer 1

the simplest inside check for the correctness of the key.
it is better to check the correctness and dates of operation of the key through tyrnet on your server.
well, and how much there is a desire to complicate the work of openers.