Комариный писк

Platform: bug-makers | Category: Steganography | Type: Challenge | Difficulty: Easy | OS: Linux | Author: XESXOR | Date: 2026-05-27 | Status: Solved Techniques: spectrogram_steganography, frequency_domain_text_hiding

Summary

Task: WAV audio file with hidden data, challenge name hints at frequency analysis (mosquito squeak). Solution: spectrogram visualization with sox reveals flag text written in the 6-16 kHz frequency band.

Комариный писк — bug-makers CTF

Description

Что скрывает этот писк?

English summary: A WAV audio file (maskito.wav) is provided. The challenge name "Комариный писк" means "mosquito squeak" in Russian, and the description asks "What does this squeak hide?" — both hinting at audio frequency analysis.

Analysis

Initial reconnaissance of the file:

• Format: RIFF WAV, 16-bit PCM, mono, 44100 Hz
• Duration: ~6 seconds (264600 samples, 529 KB)
• Raw data inspection: No embedded files (binwalk clean), no flag strings in raw bytes
• Metadata: No suspicious EXIF/metadata fields ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

The challenge name "Комариный писк" (mosquito squeak) and the filename "maskito" (play on "mosquito") are strong semantic clues pointing toward frequency/spectrogram analysis — a classic audio steganography technique where text or images are encoded as patterns in the frequency domain.

Solution

Step 1: Generate spectrogram

The key insight from the challenge name is that the data is hidden in the frequency domain, not in the time domain or raw sample values. A spectrogram converts the audio into a visual representation where the X-axis is time and the Y-axis is frequency. ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍

 bash read-only • copy allowed Copy
sox maskito.wav -n spectrogram -m -o spectrogram.png

Options used:

• -n — null output (don't produce audio)
• spectrogram — generate spectrogram effect
• -m — monochrome (better contrast for text)
• -o spectrogram.png — output file

Step 2: Read the flag

The monochrome spectrogram clearly reveals the flag text BugCTF{REDACTED} written as visual patterns in the 6–16 kHz frequency range. The text is easily readable without any additional processing.

The flag uses leet-speak: REDACTED → "easy_stegano" (3→e, 0→o). ‍​‌‌​​‌​​​‌‌​​‌​​​​‌‌​‌​​​​‌‌‌​​‌​​‌‌​​​‌​​‌‌‌​​​​​‌‌​‌‌​​​‌‌​​​​‍