Posts Tagged ‘ascii’

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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Posted in Hackvent 2019


Hackvent 2019: Day 5

05 Dec 2019
CTF: Hackvent 2019
Link to challenge:
Date Completed: 5 December 2019



HV19.05 Santa Parcel Tracking

Image mirror:


Initially we try scanning the barcode as it looks like a Code 128 barcode. It works but gives us the string Not a solution which is unfortunately a dead end. After a lot of experimentation, we manually note down the hexadecimal values for each colour in sequence. We decided to use Photoshop’s colour picker but in hindsight should have done this pragmatically using MATLAB.

This gives us the following list of 64 hex codes:

After more experimentation, we discover that the blue channel of each hex code is significant! We discard all data but the blue channel and run our sequence of hex codes through an online hex to ascii converter.

This gives us the following string which has our flag surrounded by what appears to be noise:

Flag:  HV19{D1fficult_to_g3t_a_SPT_R3ader}

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Posted in Hackvent 2019


HACKvent 2015: Day 2

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



After some Googling I realise this is the Klingon language from Star Trek.
I try some online translators (including Bing!) and it is clear that the message is a series of numbers that containor 1 only.
This is most likely binary that represents ASCII text.

I write a small script to convert each component in the text (based on a Klingon number guide):

This prints out some binary:

Total number of bits is 232 and 232/8 bits = 29 bytes.
This is exactly the number of characters in our nugget!

We convert the binary to ASCII and get the flag:

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Posted in Hackvent 2015