tldr;- known plaintext attack against consecutive digrams shift cipher- set up a system of equations representing the constraints on the key- solve the system of equations to recover potential keys
[DUCTF GitHub](https://github.com/DownUnderCTF/Challenges_2020_public/tree/master/crypto/hex-shift-cipher)
[writeup](https://jsur.in/posts/2020-09-20-downunderctf-2020-writeups#hex-shift-cipher)