Hiding messages with counterpoint.

The score for this piece has been made available online.

A reflection of the past, composed and mixed during my 7-day covid quarantine.

Time ebbs past,
As anguish holds fast.
Without you I’m filled with remorse,
For you are my one driving force.

As the season turns,
My heart still churns.
I’ll leave my sins and remorse,
Heading on a different course.

The purpose of composing this piece is threefold: it served as an expression of faith and emotions, a challenge for a Capture-the-Flag (CTF) competition, and an enjoyable way to pass quarantine. There wasn't any priority to a particular purpose; all of them seemed to develop together.

This piece was composed for the HKUST Firebird 2023 Internal CTF. Such competitions are designed to challenge players with cybersecurity know-how. Once players identify and exploit a vulnerability, they are rewarded with a flag (a piece of text), which awards points to the player when submitted. Occasionally, some challenges deviate from the norm and test players in other areas. In this case, my challenge tested players in analysing music and patterns.

When composing this piece, I aimed to compose something listenable and motivic. I decided to keep constraints flexible within limits. If a music is too constrained, it sounds choked, inevitable, or unimaginative. Some music ciphers out there encode letters into pitches and duration. This was a bit too far for my liking, as it becomes painstakingly difficult to find a pleasurable tune.

As hinted by the title, I first translated the flag into Morse using an online converter with the extended Morse character set. This allowed for some punctuation such as (, -, _, and funky non-ASCII characters such as é.

With plaintext, we need to encode at least 50 distinct letters. With Morse, we just need to encode 3 instead: ., -, and space (as a word separator). So things are relatively simple.

I toyed around with a few ideas of encoding these three characters. Eventually I ended up with this mapping:

  • . → "Note On" in upper stave (treble clef)
  • - → "Note On" in lower stave (bass clef)
  • space → "Note On" in both staves

This lent the music well to a contrapuntal form, with the occasional grace-note or glissando to pack characters in a way that preserves the melodic contour. After composing the sheet music, I ended up mixing it with Reaper for some extra flair and charged resonance, making the night seem younger.

Enjoy the result!

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