15
Sep
2014

No cON Name CTF – STEGOsaurus

Time for a stego writeup..

Can you hear it? Sounds like a flag… Note: The flag only contains lowercase characters.

$ mediainfo stegosaurus.mp3
General
Complete name : stegosaurus.mp3
Format : MPEG Audio
File size : 2.78 MiB
Duration : 3mn 2s
Overall bit rate mode : Constant
Overall bit rate : 128 Kbps
Track name : The Sub Human Spectrum Song
Performer : The Mentor

The audio is a 3 min recital of The Conscience of a Hacker (aka The Hacker’s Manifesto).

The first minute of audio appears to contain some odd low-frequency ‘pops’, so let’s open the file up in Audacity to investigate:

stegosaurus_1

For those unfamiliar with Audacity: you can press the arrow next to the track name to switch from waveform (top) to logarithmic spectrogram (bottom).

Something appears to be going on there up until the ~1m10 mark. Let’s enhance (err.. zoom):

stegosaurus_2

Looks like someone has hidden some Morse code in there. As all the morse data appears to be below 100 Hz, we can use a low pass filter (effects menu, cutoff 100 Hz) to ease transcription:

stegosaurus_3

That’s better. Now transcribe and decode it using your favorite morse decoder (I used Android Morse keyboard) to get the flag:

NCN3cbfdcc8d7a257d8062560e88dd7d7fd65dc647a

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