Cryptic File Challenge
The other day, a friend of mine sent me a mysterious file that was part of a challenge. Feel free to grab a copy below if you’d like to follow along!
Named “file1”, it appeared to just be a binary file. Perhaps a common file with it’s extension removed? Opening it up in a text editor, I saw mostly garbage. With such little legible data in the header, I had to do some digging. “REDACTED” didn’t seem helpful, so I Googled “reference lib 1.3.0 20130526” in hope of finding anything related. I was immediately confronted with a bunch of results relating to FLAC (“free lossless audio codec”). Hmm…
Maybe this is actually a FLAC file without the extension? Perhaps appending “.flac” to the filename and testing it out will help? I changed the extension, tried opening it in VLC, and got a whole lot of nothing.
This part had me a little stumped (and I was juggling this mystery along with my duties at work) so I stopped for a bit. Not too long afterwards, a friend said he figured out the file. When compared to a normal FLAC file, you could see the “REDACTED” part was replacing the “fLaC” that is found in the header of a standard FLAC file. For reference, I downloaded a free FLAC sample to compare.
After replacing “REDACTED” with “fLaC” and saving the file, I gave VLC another go. (Note: tampering with binary files in Notepad/Atom/whatever might break things due to character encoding. For example, making the change with Notepad “fixed” the file but it still wouldn’t play. I made the changes with nano just to avoid any character encoding issues.)
Now I had a fully readable FLAC file that was 50 seconds long! Playing the track gave me a fun little orchestral piece by Bill Conti (I forget the track, but you can figure that out with Shazam/Google as you solve this puzzle with me ;p ) but at the end there was a long delay before a strange tone. It almost sounded like one of the sounds you’d hear when using a dial-up modem. Surely, this was there for a reason so I decided to take a peek at the audio with Audacity and see what the tone at the end was all about. I was on a hunch since I had just recently read about the developers of the recent DOOM hiding symbols and numbers in the spectrogram of a song from the game.
Above you can see the entirety of the strange tone that played at the end of the track. It looked very “generated” and unnatural due to the consistency of the peaks. Also, it seemed like “chunks” as each group of peaks contained 4 or 5 distinguishable peaks.
“This is something.” Out of sheer curiosity (and luck, I suppose), I pulled up a Morse code chart and tried to see if this lined up in any way since there are large peaks and small peaks in the waveform (like “short” and “long” in Morse code).
So, four small peaks and one large one would be a “4” in Morse code. Followed by another. Followed by one small peak and four large peaks; a “6” in Morse code. You get the idea (hopefully). The tone at the end of the song was generated noise that was just Morse code when broken down.
After deciphering the entire waveform of Morse code, I ended up with a string of random characters… 446F20596F752048617665205468652052696768742053747566663F
This looked like hexadecimal since the alphabetic characters never surpassed “F” and the rest were digits. I’ve come across plenty of hex strings in challenges like these, so I may take that sense for granted. Off to Google for a HEX to ASCII converter! The first one I found was here and it looked like it would do the trick…
Apparently I had the right stuff because that answer was correct! I love cryptic stuff like this [: