This is an article about three different licensing systems, using C#.NET environment.

Title: Three different algorithms for constructing licensing systems, their advantages and disadvantages using C# .NET environment.

Abstract: A key validation algorithm is one of the important parts in the protection of a computer application. Even if an already existing API is to be used, it is important to understand its weaknesses in order to compare it with alternative ones. Therefore, in this article, three different categories will be described with clear definitions that will make it possible to distinguish between them and allow an analysis of currently existing APIs. Every category is accompanied with examples and in some cases suggestions for further development. The categories described in this article are Checksum based key validation, Pattern based key validation, and Information based key validation. It is going to be found that the choice of a key validation system depends on the information that is to be stored in the key. It is also concluded that at this point it would be better to use online key validation instead.