Skip to content

Audio Steganography

The audio-related CTF challenges mainly use steganography techniques, involving MP3, LSB, waveform, spectrum steganography.

Common Method

Finding and extracting information using binwalk and strings commands, details are not converted.

MP3 Steganography

Basics

MP3 steganography is using the MP3stego tool to hide information. The basic introduction and usage are as follows:

MP3Stego will hide information in MP3 files during the compression process. The data is first compressed, encrypted and then hidden in the MP3 bit stream.

encode -E hidden_text.txt -P pass svega.wav svega_stego.mp3
decode -X -P pass svega_stego.mp3

CTF Example

ISCC-2016: Music Never Sleep

After the initial observation, no flag was found with strings and the audio was normal. so steganography tool was likely used to hide the flag.

After decoding using Mp3Stego with the password found earlier.

decode.exe -X ISCC2016.mp3 -P bfsiscc2016

We got the file iscc2016.mp3.txt:

Flag is SkYzWEk0M1JOWlNHWTJTRktKUkdJTVpXRzVSV0U2REdHTVpHT1pZPQ== ???

After decoding the encoded string from base64 and base32, we got the flag.

Waveform

Basics

--..----.----.

Generally speaking, we want to observe the waveform pattern of an audio file to find something strange. We can use tools like Audacity or Adobe Audition to do that. After the waveform pattern, see if you can convert part of the waveform into binary strings (1s and 0s). See

CTF Example

ISCC-2017: Misc-04

In fact, the hidden information in this challenge is in the first part of the audio. If you don't listen carefully, you may mistake it for steganography.

Download the challenge here

The high is 1, and the low is 0, representing a binary string (1s and 0s).

110011011011001100001110011111110111010111011000010101110101010110011011101011101110110111011110011111101

Convert to ASCII. Note that one group of binary must be 7 bits because the length of the binary string is 105, it can't divide into 8 bits evenly (105 mod 8 is 1), however, it does divide into 7 (105 mod 7 is 0).

Spectrum

Basics

Spectrum stenography is hiding strings in the audio spectrum. One distant feature is that it often contains noisy or harsh sounds.

CTF Example

Su CTF Quals 2014: hear_with_your_eyes

Download the challenge here

Open the audio in Audacityand view the spectrogram.

LSB Audio Steganography

Basics

Similar to LSB in image steganography, you can also perform LSB steganography in audio. we can use the SilentEye tool to solve audio LSB challenges.

Description of SilentEye:

SilentEye is a cross-platform application design for an easy use of steganography, in this case hiding messages into pictures or sounds. It provides a pretty nice interface and an easy integration of new steganography algorithm and cryptography process by using a plug-ins system.

2015 GDQWB: Little Apple

Just use slienteye's decode feature.

本页面的全部内容在 CC BY-NC-SA 4.0 协议之条款下提供，附加条款亦可能应用。

Comments