Hackvent 2019: Day 7

08 Dec 2019
CTF: Hackvent 2019
Link to challenge:
Date Completed: 7 December 2019


HV19.07 Santa Rider


For easy download, get it here:


We watch the provided video and notice that about half way through the LEDs light up in an interesting order. There are 8 total LEDs and multiple LEDs light up at once so we think that this may be hidden binary messages that decode to ASCII. As the video moves very fast its necessary to inspect each frame individually. We can do this by extracting each frame using a tool like FFmpeg but in this case it was faster to simply use a video editor like MPC-HC which allows you to navigate the video frame by frame.

It is very cool to note that because the video is stationary and position of LEDs do not move, one could use a computer vision library like OpenCV to extract the hidden binary.

We get the following binary:

We convert this binary to ASCII and get our final flag!

Flag:  HV19{1m_als0_w0rk1ng_0n_a_r3m0t3_c0ntr0l}


This challenge also contained the solution to HV19.H2 Hidden Two

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