See seanjoflynn.com/research/bittorrent for the full write up.
The aim of this project was to gain a better understanding of the technical details of the BitTorrent protocol. In terms of the depth of the research, I like to get to the point where I have a good idea of what I don't know. BitTorrent is actually a great topic as it covers a lot of different areas: HTTP, TCP, custom encodings, cryptographic hashing, file IO and (optionally) multi-threading. I used C# as it's the language I'm most familiar with. I essentially built version 1.0 of the protocol, however further additions are necessary before it would be able to be tested in the real world).