Forensics – Moonwalk_1

Moonwalk - 250pts.

Challenge

Decode this message from the moon. https://2019shell1.picoctf.com/static/f5ca745ad5d88a890b5f20b8ffde3d70/message.wav

Hints

How did pictures from the moon landing get sent back to Earth?
What is the CMU mascot? that might help select a RX option

Solution

we have a file called message.wav with the flag to decode inside. When we open the file we can hear a series of seemingly meaningless noises
and "beeps".
We understand that the file contains a "SSTV signal" (slow scan television, a radio transmission system by now mainly used by
amateur radio for sending static images, which in the past was also used for sending images from space).
to decode it we install a software called QSSTV (compatible with linux) suitable for decoding this type of signals.

software configuration

once the software is installed:
1) open the software and go to Options -> Configuration -> Audio -> select PulseAudio on audio interface and sound input: from
sound card.
2) we return to the main screen and on standard file format we set .png
3) mode we set it to Scottie 1 (this is the encoding system used by the signal)
4) max db range is set at + 50 / -40 db
5) avg is set to 0.80
6) Sensitivity: High

after setting these values in the respective fields, we can start decoding the signal

decoding of the signals

We put QSSTV in listening mode (by pressing the receiver start button from the main screen) and at the same time we reproduce the signal audio,
the computer's microphone will listen to the signal and send it to the software that decodes it.
if all the steps have been carried out correctly the software will return us a .png file.
once the message is decoded, we open the image obtained, just turn the image and read the flag!

picoCTF{beep_boop_im_in_space}

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