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Most of the challenges deal with Steganography using specific tools like Binwalk or Zsteg to solve them. Hence, we will only focus on challenges which are more unique.

Extraterrestrial Communication (200 pts)

Aliens have recently landed on the moon and are attempting to communicate with us.
Can you figure out what they are trying to tell us?

We are provided with a mp3 file with some weird screeching sound. From the title, we know that it could be some unique method to communicate or send data using sound signals.

From a quick google search, we quickly discover that it seems like SSTV.

Downloading qSSTV for Linux, and following an online tutorial to set it up, we successfully obtained the image (and flag).

Screenshot of SSTV image

Flag: dctf{wHat_ev3n_1s_SSTV}

Author: @wonyk

Bad Apple (200 pts)

Someone stumbled upon this file in a secure server. What could it mean?

We are provided a mp4 file with a music video for the popular song Bad Apple. The difference is that in this particular version, there is about 10 seconds of high pitched audio in the center of the video.

To solve, I first use ffmpeg to extract the 10 seconds of screeching in mp3 format before passing the audio to Audacity and perform a spectral analysis.

From there, we can manipulate it to make it a QR Code.


You need to flip the QR Code image to reveal the flag

QR Code

Flag: dctf{sp3ctr0gr4msAreCo0l}

Author: @wonyk

Powerpoint Programming (200 pts)

A login page in powerpoint should be good enough, right?

Flag is not in format. DCTF{ALL_CAPS_LETTERS_OR_NUMBERS}

Sounds interesting - powerpoint has programming abilities?!

For this challenge, we are provided with a .ppsx file – chall.ppsx

Here is a snippet of the file:


Simply pressing the buttons randomly will result in this page:

Wrong screen

To get the "source code" of the ppsx file, I open the file in Microsoft Powerpoint instead of directly clicking the file open (since it was in .ppsx - Powerpoint Slide Show format).

Scrolling through the file, I noticed this at the animations tab:

Animation pane

Following the train of process of the animation flow in the file, we are able to solve the challenge and get the flag.


Author: @xbowery