write-up: Passe ton Hack d'abord 2024: 1 programming challenge

I’ve tried to do some challenges during that CTF. Here’s my solution for the first programming challenge:

from pwn import *

r = remote('37.59.31.202', 2000)

print(r.recv(1024))

r.sendline(b'1')
print(r.recv(1024))

i = 1
while True:
    i += 1

    if i == 102:
        print(r.recv(1024))
        break

    evaluated = eval(r.recvline().decode())
    print("[*] evaluated: {}".format(evaluated))
    r.sendline(str(evaluated).encode())
    
    
r.close()

Write Up - FCSC 2023

About this

I did some challenges from the France Cybersecurity Challenge of this year, so here just 2 write ups (cuz I may not be really good at explaining how to solve shit). I didn’t solved any tricky chall due to my lack of implication in the CTF, but some of them were pretty fun though, so thanks to the organizers.

I finished 618/1364 on global ranking, and 67/188 on junior ranking.

Write Up - CTF After Dark Winter 2023: Jester

Informations

CTF: CTF After Dark Winter 2023 Author: Jerry

Challenge

Let’s start with some addition: What is 7381 + 8074 ? Oh yeah, I think I forgot to mention. As an extra bonus to make sure you are learning, these numbers change every second :) Tee hee! Good luck keeping up!

(https://jester.acmcyber.com/)

We first encounter a page that ask us to compute an addition on random numbers in less than a second. We’ll obviously code a script that scrap the page, compute the addition, and send back the result in the submit.

Write Up - IrisCTF 2023: babynotrsa | Why you should beware tweaking RSA

Video version (French)

Sincere acknowledgements to aaSSfxxx who helped me a bit with mathematical demonstrations and kindly read my write up before I posted it.

This challenge is one of the ones I flagged during the IrisCTF 2023. Thanks to the organizers, I didn’t tried lots challenges but that one was particulary fun as a beginner.

Challenge

Name: babynotrsa Author: sera Description:

Everyone knows RSA, but everyone also knows that RSA is slow. Why not just use a faster operation than exponentiation?