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Digital Overdose 2022 CTF Area 51

digitaloverdose2022 steganography Area 51

File: challenge.wav download

Challenge/Competition: Digital Overdose 2022

Challenge Discription: An alien that fled Area 51 has trusted a civilian to transmit a message.What did it contain?

File

we got a audio (wav) file and we have to extract our Flag from it

After looking around on the internet for audio steganography, I came across the term spectrum analysis

Spectrogram

Here is a quote from Wikipedia:

A spectrogram is a visual representation of the spectrum of frequencies of a signal as it varies with time. When applied to an audio signal, spectrograms are sometimes called sonographs, voiceprints, or voicegrams. When the data are represented in a 3D plot they may be called waterfall displays.

here is a spectrogram image for spoken words “nineteenth century” with audio frequency shown on y axis and time on x axis

Spectrogram of the spoken words "nineteenth century". Frequencies are shown increasing up the vertical axis, and time on the horizontal axis. The legend to the right shows that the color intensity increases with the density. - wikipedia

Getting the Flag

Now all we have to do is use a method or a tool to translate this audio to its corresponding spectrogram image.

i am going to use “Sonic Visualiser” for this purpose

Lets open out audio file within Sonic Visualiser and add spectrogram pane from “menu>Pane>Add spectrogram” or press “G” for shortcut

after some twaking with size we can clearly read the flag

DOCTF{SP3CTR0GR4M5_4R3_C00L_1F_0NLY_1_KN3W_H0W_T0_CR34T3_1T_MY53LF}