Writeup DGSE - CTF - Définition

This article describes my solution for the 50-point challenge called “Définition”.

Introduction

Un de vos collègues a créé un petite énigme, il est un peu lourd et vous demande depuis des semaines de la résoudre, faites lui plaisir.
Voici l'énigme : Quelle heure est-t-il ?
Connectez-vous via nc challengecybersec.fr 6660
Le flag est de la forme : DGSESIEE{x} avec x un hash

Start

Let’s try to help our colleague. To access the challenge you need to open a connection with netcat on port 6660.

nc challengecybersec.fr 6660
Entrez la reponse:
 > 18 heures 12
Mauvaise reponse !

Well, he doesn’t seem very cooperative. Remember that behind it is still a computer (although we are told it is a colleague). Computers work differently from us, they are based on the number of seconds that have elapsed since January 1, 1970. You’ve probably already heard about it, it’s often called epoch time, UNIX time or even UNIX epoch time.

Under GNU/Linux, you can retrieve this value with the command date.

date +%s
1604772765

Let’s try to send it to him.

date +%s | nc challengecybersec.fr 6660
Entrez la reponse:
 > Bravo ! Voici le flag : DGSESIEE{cb3b6481e492ccc4db7374274d23c659}

It’s better when you use the right words!