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)

Original writeup (https://jsur.in/posts/2020-09-20-downunderctf-2020-writeups#hex-shift-cipher).