BSides Brisbane 2019 CTF - emoji
Category: misc
Points: 200
Solves: 4
Description: There’s always one of these, isn’t there? flag is of the format flag{text}. Plus a download in the form of emoji.txt.
emoji.txt contents:
😀😀😀😀😀😀😀😀😀😀[🙃>😀😀😀😀😀😀😀😀😀😀<]>😀😀.😀😀😀😀😀😀.<😀😀😀[🙃>🙃🙃🙃<]>🙃🙃.😀😀😀😀😀😀.<
😀😀😀😀[🙃>😀😀😀😀<]>😀😀😀😀.<😀😀😀😀😀😀[🙃>🙃🙃🙃🙃🙃🙃<]>🙃🙃🙃.<😀😀😀😀[🙃>😀😀😀😀<]>😀😀😀
😀.<😀😀😀😀😀😀😀[🙃>🙃🙃🙃🙃🙃🙃🙃<]>🙃🙃🙃🙃🙃🙃.<😀😀😀😀😀😀😀😀[🙃>😀😀😀😀😀😀😀😀<]>😀😀.<😀😀😀
😀[🙃>🙃🙃🙃🙃<]>🙃🙃🙃🙃.<😀😀😀[🙃>😀😀😀<]>😀.<😀😀😀[🙃>😀😀😀<]>😀.<😀😀😀😀[🙃>🙃🙃🙃🙃<]
>🙃🙃🙃🙃.<😀😀😀😀[🙃>😀😀😀😀<]>😀😀😀😀😀.<😀😀😀😀😀😀[🙃>🙃🙃🙃🙃🙃🙃<]>🙃🙃🙃🙃🙃🙃🙃🙃.<😀😀😀😀
[🙃>🙃🙃🙃🙃<]>🙃🙃🙃🙃🙃.<😀😀😀😀😀😀[🙃>😀😀😀😀😀😀<]>😀😀😀😀😀😀😀😀.<😀😀😀😀[🙃>😀😀😀😀<]>😀
😀😀😀.<😀😀😀😀😀😀😀😀[🙃>🙃🙃🙃🙃🙃🙃🙃🙃<]>🙃🙃🙃.<😀😀😀😀😀😀😀[🙃>😀😀😀😀😀😀😀<]>😀😀😀😀😀😀😀😀
😀😀😀😀😀.🙃🙃🙃🙃🙃🙃🙃.🙃🙃🙃🙃🙃🙃🙃🙃.<😀😀😀😀[🙃>😀😀😀😀<]>😀😀😀😀😀.<😀😀😀[🙃>🙃🙃🙃<]>🙃🙃🙃
.<😀😀😀😀😀😀😀[🙃>🙃🙃🙃🙃🙃🙃🙃<]>🙃🙃🙃.<😀😀😀😀😀😀😀😀[🙃>😀😀😀😀😀😀😀😀<]>.<😀😀😀😀[🙃>🙃🙃
🙃🙃<]>🙃🙃🙃🙃🙃.😀😀😀😀😀.<😀😀😀😀😀😀😀[🙃>🙃🙃🙃🙃🙃🙃🙃<]>🙃🙃🙃.<😀😀😀😀😀😀😀😀[🙃>😀😀😀😀😀😀
😀😀<]>😀😀😀😀😀😀😀😀😀😀.<😀😀😀😀[🙃>🙃🙃🙃🙃<]>🙃🙃🙃🙃🙃.😀😀😀😀😀😀😀😀😀.<😀😀😀[🙃>🙃🙃🙃<]>
🙃🙃🙃🙃🙃🙃.<😀😀😀😀[🙃>😀😀😀😀<]>😀😀😀😀😀.<😀😀😀[🙃>🙃🙃🙃<]>🙃🙃🙃🙃🙃🙃.😀😀😀😀😀😀😀😀😀.<😀
😀😀[🙃>🙃🙃🙃<]>🙃.<😀😀😀😀😀[🙃>😀😀😀😀😀<]>.<
Though some may recognise it, googling programming languages should reveal the syntax belongs to the esoteric programming language “Brainfuck”, however, + has been substituted with 😀, and - substituted with 🙃. Change these back using whatever tool you want (find + replace in VSCode was enough for me). Running this through an interpreter, such as copy.sh/brainfuck/ reveals the flag: flag{Th1s_is_tH3_s0ng_th4t_d0zen_tend}
I didn’t solve emoji on the day, but went back to have a look after solving Brainy’s Cipher on HTB and got the flag.