Forensics: This is a broad category that includes different types of training challenges such as file format analysis, steganography, memory dump analysis, or network packet capture analysis.
Web Exploitation: This category includes all the challenges that provide a vulnerable website, from the ones that contains a bug to the ones that run over an old version of a framework.
Reverse Engineering: It is typically the process of taking a compiled (machine code, bytecode) program and converting it back into a more human readable format.
Binary (PWN): Binary exploitation is the process of subverting a compiled application such that it violates some trust boundary in a way that is advantageous to the attacker. It comes down by abusing vulnerabilities that corrupt memory in software or by finding a vulnerability in the program and exploiting it in order to escalate privileges.
Cryptography: the main goal is usually to crack or clone cryptographic objects or algorithms to reach the flag.
Very Easy: It requires just one step in order to get the flag
Easy: It requires one-two steps, it is based on the challenge category
Medium: It requires two-three steps, it is based on the challenge category
Hard: It requires three-four steps based on the challenge category
Very Hard: It requires several steps in order to get the flag