Challenge Description
Description
There’s more than meets the ear. I think there’s something hidden in this audio.
- Author: Jun Wei
- Category: forensics
- Difficulty: easy
Files
There’s More Than Meets The Ear - Solution
What is a spectrogram?
A spectrogram is a visual representation of the frequencies present in an audio signal over time. The x-axis represents time, the y-axis represents frequency, and the colour/intensity represents amplitude at each frequency.
Hidden messages can be embedded in the high-frequency range of audio files, where they are inaudible to the human ear but visually visible in the spectrogram. This is a common audio Steganography technique in CTF challenges.
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Download the audio file (
cool.wav) provided. -
Open the file in Audacity. By default, Audacity displays the waveform view. To switch to the spectrogram:
- Click on the track name (left panel) → select Spectrogram from the dropdown.
- Alternatively, go to the track’s dropdown arrow →
Spectrogram.
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Look for text patterns in the spectrogram. The flag should be visible in plain text within the frequency bands.
Simply read the flag from the spectrogram image.
The submissions for this challenge were strangely interesting, although my peers and I thought this was a relatively easy challenge and the flag was easy to read.
But after reviewing the flags people actually submitted and the avalanche of tickets (+ DMs) I got just for this one challenge, I’m starting to suspect some of you were reading hieroglyphics instead of the flag. Either that, or the flag grew legs and ran away. 😆
Flag: HNF25{h1dd3n_in_audi0}