The workshop will be about clean-room reverse engineering of unknown file formats. With some examples (from simple to complicated), we will discuss the usage of Kaitai Struct for quick formulation and testing of hypotheses re file format. We will go from software installation up to coding ready-to-use utilities applicable to the file formats on C++, C#, Java, JavaScript, Perl, PHP, Python, and Ruby, and will also review container formats, file systems, firmware formats, bite-code and many others.