HACKvent 2015: Day 7

07 Dec 2015
CTF: Hackvent 2015
Link to challenge:
Date Completed: 07 December 2015



This challenge was very easy to solve as I had completed the teaser earlier.

First I convert the hexadecimal number provided (as it starts with 0x) to binary.
The result is 625 bits (which does not divide nicely by 8 so it is probably not an ASCII message).

However, its likely to be a QR code version 2 which is 25×25 = 625 pixels large.
In this case, every 1 corresponds to a black pixel and every 0 corresponds to a white pixel.
This is obvious by arranging the bits into a 25 by 25 grid and adding some spacing :

I use the same script I used in the teaser (link) to generate a QR code.
This is the QR code generated (enlarged to 350px * 350px):

Day 7 QR Solution

We scan the QR code using a really clever online scanner (link) that has some extra error correcting capabilities (compared to other QR readers).
We get the flag:  HV15-aFsf-4ea1-2eGg-Llr4-pB5A


Posted in Hackvent 2015


Leave a Reply


  1. Someone

    December 9, 2015 at 3:04 AM

    You know that the event is still running and you can get points for the solution

    • Mohammad Ghasembeigi

      December 9, 2015 at 12:24 PM

      These are part of my write up and i’m releasing it after the day you can get full points on. There is nothing to gain by cheating as this CTF is for fun.

  2. Someone

    December 9, 2015 at 3:27 AM

    And you tags have spoilers 😐

    • Mohammad Ghasembeigi

      December 9, 2015 at 12:25 PM

      Then maybe don’t search for write ups so you aren’t spoilt?