KnightCal

Introduction

Hi! For my first write-up, I decided to write about something easy. Enjoy :D

First Glance

The target site is pretty simple, we can enter numbers and math expressions then it will calculate the result for us hence the name “KnightCal”

      Figure 1

Unnecessary Feature???

If you look at the results it’s giving us, we get additional information “File already exists with name: d.txt”

After playing with it I concluded that each number represents a certain letter. For example in Figure 1 2 == d.txt When we enter 22, the result is dd.txt. This means that it concatenates the string based on what the number represents.

Numbers –> TXT –> flag.txt

The next thing I did was to get all of the letters that the numbers 1-9 represented.

1 = l.txt
2 = d.txt
3 = b.txt 
4 = h.txt
5 = g.txt
6 = c.txt
7 = f.txt
8 = e.txt
9 = a.txt

and since this is a CTF the first thing that came to my mind is to enter the numbers that will result in flag.txt

7195 == flag.txt

And that’s how we get the flag :P

      Figure 2

That’s all for this writeup. Thanks for reading and have a nice day :D

-Datsuraku147