Given an encrypted document and the length of the key used (4).

Name of challenge hints at xor.

Use [xortool](https://github.com/hellman/xortool) to brute force the possible keys of length 4.

* Feed `-c '\x00'` as most common character as well, guessing that the document is a txt document.

Turns out decrypting as not "95%+ valid english plaintext", but the document is actually decoded; just doesn't seem so to XORtool because it's a word doc. Open the one resultant file manually as a word doc and see the flag.

[See full writeup for more details](https://bigpick.github.io/TodayILearned/articles/2020-06/nahamConCTF-writeups#docxor)