https://ctftime.org/event/1209
X-MAS CTF 2020 was HTsP’s third installment of X-MAS CTF. The event lasted for 5 days but I was only able to squeeze in one challenge.
Biggest Lowest
This was a Netcat-based game where you were served a random array of numbers and a count (k) for the biggest and lowest sets. First set (K1) had to be sorted in ascending order, the second set (K2) sorted in descending order and then concatenated with a ; and returned as an array.
Example:
[8,5,6,3,9,2,1]
K1 = 3
K2 = 5
Answer:
[1,2,3;9,8,6,5,3]
After sending back the correct answer another more complicated (longer) array would be presented. A timer ensured that no human would be able to complete the challenge manually.
My solution was a very poorly written Python script which was atleast able to beat the game and captured the flag.
Script: biggest-lowest.py