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!

Is this a compiled program that someone broke? Or maybe an image without it’s extension?

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…

It can’t be a coincidence when you get a barrage of similar results. Let’s dig deeper…

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.

Hitting play did absolutely nothing. It also wasn’t pulling metadata or any codec info, so the file could be broken.

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.

Those sneaky creators redacted the “fLaC” from the header. No wonder it was broken.

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.)

You can see the difference between how nano displays the text within the file (here) and how Atom displayed it (above). Making changes with Atom or Notepad didn’t work, so I used nano inside bash on Windows 10 AE (excite!).

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.

I had to do this part on my Macbook due to Audacity crashing when trying to open FLAC files on my WIndows 10 system.

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.

A closer look at the peaks of the generated tone.

“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).

Courtesy of Wikipedia (https://commons.wikimedia.org/wiki/File:International_Morse_Code.svg)

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.

Converting the peaks into Morse code gave me some sort of message. Compare these against the chart above to see how I came up with these values!

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…

When converted from hexadecimal to ASCII, the string became a readable sentence “Do You Have The Right Stuff?”

Apparently I had the right stuff because that answer was correct! I love cryptic stuff like this [:

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