picoCTF General Skills Guide

Nice netcat...

Name: Nice netcat...
Description: There is a nice program that you can talk to by using this command in a shell: $ nc mercury.picoctf.net 43239, but it doesn't speak English...
Author: syreal
Tags: Easy, General Skills, picoCTF 2021
Challenge from: picoCTF 2021
Hints:
1. You can practice using netcat with this picoGym problem: what's a netcat? (Guide)
2. You can practice reading and writing ASCII with this picoGym problem: Let's Warm Up (Guide)

Theory

According to the description, to get the flag we have to enter to a NetCat, but it doesn't speak English. I'm gonna go ahead and guess that it's going to be another one of those conversion things of like hex, decimal, binary, base64, etc. That kind of stuff.

Solution

Let's enter to the NetCat:

shukularuni-picoctf@webshell:~$ nc mercury.picoctf.net 43239
112 
105 
99 
111 
...

It seems to be decimal, because I see numbers 0-9 but no letters, so if we remove the new lines between them, we can convert them back to text:

DECIMAL to TEXT (ASCII)

INPUT: 112 105 99 111 67 84 70 123 103 48 48 100 95 107 49 116 116 121 33 95 110 49 99 51 95 107 49 116 116 121 33 95 55 99 48 56 50 49 102 53 125 10 

OUTPUT: picoCTF{g00d_k1tty!_n1c3_k1tty!_7c0821f5}

There we go! That's the flag.

I rated this level as "good"! :3