The pcap contains game traffic of cs:go which is encrypted with "ICE". The key can be generated by using the build number.
After decrypting the traffic the flag can be extracted by shifting the bits, as the protcol used by valve is based on bitstreams. All this information can be obtained by reverse engeneering the engine ;)
OR (and this is the reason I rated it as easy) by reading [this post](https://www.unknowncheats.me/forum/counterstrike-global-offensive/292668-networking-megathread.html)
I got the idea for this challenge when I was developing a fuzzer for cs:go. (which I never finished and instead ended up as a plug'n play cheat by using my mobile phone as a network sniffer and mouse emulator, more like a proof-of-concept as I don't even play games ;) [Video](https://www.youtube.com/watch?v=nn_hD1-Xe5Q) )

Original writeup (https://github.com/OlfillasOdikno/CAMP-CTF-2019/tree/master/solutions/Kuchenblech/stage3).