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m00nwalk

Problem

Decode this message from the moon. You can also find the file in /problems/m00nwalk_6_811c5485a374101cc212434dc2601130.

Solution

  1. 1.
    The hint suggests that this is related to how images from the moon landing were transmitted back to earth. Some research leads to SSTV. Note: Originally I solved this challenge using this program for Windows but since then I found an easier way that works within Kali Linux (see next step).
  2. 2.
    This tutorial (Archive) explains how to convert the audio file to an image.
  3. 3.
    Install qsstv with apt-get install qsstv
  4. 4.
    Run pactl load-module module-null-sink sink_name=virtual-cable
  5. 5.
    Run pavucontrol. A GUI will pop-up, go to the "Output Devices" tab to verify that you have the "Null Output" device.
  6. 6.
    Run qsstv. The program GUI will pop-up, go to "Options" -> "Configuration" -> "Sound" and select the "PulseAudio" Audio Interface
  7. 7.
    Back in the pavucontrol GUI, select the "Recording" tab and specify that QSSTV should capture audio from the Null Output
  8. 8.
    The hint asked "What is the CMU mascot?" - the answer is "Scotty the Scottie Dog". This hinted that we should select "Scottie 1" as QSSTV's "Mode". Select "Auto Slant" as well.
  9. 9.
    Run paplay -d virtual-cable message.wav to create the image:
    QSSTV finished image
  10. 10.
    Unload the virtual audio cable so audio will play normally:
    $ pactl list short modules | grep null
    25 module-null-sink sink_name=virtual-cable
    $ pactl unload-module 25

Flag

picoCTF{beep_boop_im_in_space}