Challenges of this type focus on finding and using vulnerabilities in a cryptographic protocol, primitive or a particular implementation. Challenges of this kind are usually most demanding in theoretical knowledge.
Within this type, the goal is to build an exploit, very often for a binary, though sometimes for a Web application.. Problems within this category are usually the most difficult with regards to technical knowledge.
The purpose here is to explore a given binary file and to find the key by decompilation, static or dynamic analysis or other reverse engineering tools.
This type of challenges focus on finding and leveraging vulnerabilities in websites/webapps.
The main goal in this category is to “investigate” some sort of data, like a network capture (e.g. a .pcap file) and finding the “needle” in the “haystack”.
Everything not listed else that is still relevant to Information Security is in this category.