spEC

Reverse Engineering

$${\color{red}Overview:}$$

We are given a .zip file called “spEC.zip”. We need get the answer in hacker{XXXX}.

$${\color{red}Theory:}$$

Audio can hide hidden messages through a spectrogram. The waveforms of audio files can be converted to spectrograms to display hidden images or text. We can decode these hidden messages using programs such as Audacity or specific webpages. Similarly, Image files may also hide such data using spectrographs. Also text may be encrypted using multiple algorithms to hide data.

$${\color{red}Solution:}$$

1. A .zip file is provided to the player with 3 files within it: 1 .wav audio file, 1 poster.png & divergence.7z.

2. The .7z file is password protected.
3. Using a steganography decoder doesn’t reveal anything from the image.
4. Using a spectrograph decoder on the.wav reveals this: We can open the audio file in a program such as Audacity.

When using Audacity, use the spectrogram option as shown below.

5. The message: “FORMAT: YYYY:MM:DD HH:MM:SS” is revealed from the file.
6. This may mean that the creation date of the image is the password of the .7z file.
7. Using exiftool on the image reveals:

8. Trying the File Modification Date/Time as the password for the .7z file unlocks the file.
9. This reveals a .png file.
10. Running this file through a steganography decoder reveals some binary text.

11. Converting this binary text to human readable form gives a randomly generated looking string. Since it ends with ‘=’, we can assume it may be a base64 encrypted text.

12. Decoding the base64 reveals our flag

$${\color{red}Flag:}$$

$${\color{lightgreen}hacker(kopafjb8734hoc0qd)}$$