This article is devoted to the development of the key licensing system for the applications. In the theoretical part of the article, we will examine the cryptography methods, which can be used while implementing the licensing system. Also we will discuss all pros and cons of these methods and select the possible ones for using in the application. In the practical part of the article, we will provide the implementation of the simplest licensing system, which guaranties the protection from cracking even if a hacker knows the source code of an algorithm.