CTF write-ups

How the OKIOK team solved capture-the-flag challenges at NorthSec and elsewhere: the full solution, the tools used, and the dead ends on the way there.

14 articles

• May 23, 2025

  NorthSec 2025 Challenge Writeup – Vending Machine Encoded Messages

  This post follows up on the solution to the vending machine challenge from NorthSec 2025.

• May 21, 2025

  NorthSec 2025 Challenge Writeup – Vending Machine NFC

  My colleague François Caron and I, Étienne Ducharme, took on an interesting challenge at the NorthSec 2025 cybersecurity competition (CTF).

• September 9, 2023

  NorthSec 2023: AskG.O.D (SQL Challenge)

  This post is a writeup of the AskG.O.D track that we did at NorthSec 2023. Introduction This was the introduction to the challenge.

• September 9, 2023

  NorthSec 2023: Orchestry (Java RCE challenge)

  This post is a writeup of the Orchestry track at NorthSec 2023.

• July 26, 2023

  AmateursCTF 2023 – Censorship challenges (python jails)

  From the 15/07/2023 to the 19/07/2023 took place the AmateursCTF.

• June 19, 2022

  NorthSec 2022 Challenge Writeup – Internal Network

  OKIOK attended the annual NorthSec event, and participated in their CTF.

• May 20, 2020

  NorthSec 2020 Exam Solutions Challenge Writeup

  The following post describes the way I solved the challenge Exam Solutions from the NorthSec 2020 CTF.

• May 20, 2020

  Cyber Beats NSEC 2020 Write up

  In the last Northsec event, I had the chance to play with a fun audio challenge.

• March 14, 2014

  NorthSec 2013 – Smart Card Track – Part 6

  This is the sixth and final part of the story of the smart card track at NSEC 2013. You can see the first five parts: part 1, part 2, part 3, part 4 and part 5.

• February 28, 2014

  NorthSec 2013 – Smart Card Track – Part 5

  This is the fifth part of the story of the smart card track at NSEC 2013. You can see the first four parts: part 1, part 2, part 3 and part 4.

• February 21, 2014

  NorthSec 2013 – Smart Card Track – Part 4

  This is the fourth part of the story of the smart card track at NSEC 2013. You can see the first three parts: part 1, part 2 and part 3.

• January 31, 2014

  NorthSec 2013 – Smart Card Track – Part 3

  This is the third part of the story of the smart card track at NSEC 2013. You can see the first two parts: part 1 and part 2.

• January 17, 2014

  NorthSec 2013 – Smart Card Track – Part 2

  This is the second entry about the smart card track at NorthSec 2013, if you missed the first one, read it here.

• January 8, 2014

  NorthSec 2013 – Smart Card Track – Part 1

  I want to post in this blog what I did at NorthSec 2013 which is a hacking competition that took place in Montreal in April 2013 (www.nsec.io).