Solstice Cipher - A Bletchley Park Tribute to Alan Turing

This is a submission for the June Solstice Game Jam

What I Built

Solstice Cipher is a browser-based codebreaking puzzle game where you play a WWII-era codebreaker at a Bletchley Park-style station, racing to decrypt intercepted enemy transmissions before daylight runs out.

Each level introduces a different real cryptographic technique — starting with a simple Caesar shift, moving into substitution ciphers, and finishing with a Vigenère cipher — all decoded using an in-game "Decrypt-O-Matic" terminal helper that teaches the underlying logic instead of just asking you to guess.

The solstice theme isn't just cosmetic: every level is timed by a daylight meter that drains at different speeds depending on whether the in-game date falls on an "odd" or "even" day, mirroring how the June solstice means radically different day lengths depending on which hemisphere you're in. The in-game calendar counts up toward Day 21 — June 21, the solstice itself, which is also the final cipher level.

After the last cipher, the game shifts gears entirely: you're presented with four short text passages and asked to judge which were written by a human and which were generated by a machine — a direct nod to Alan Turing's 1950 "Imitation Game" proposal. The passages are intentionally ambiguous (one "machine" passage sounds very natural, one "human" passage sounds a little stiff) so the moment actually makes you think, rather than being an obvious gimme.

The game closes with a short, factual dedication to Alan Turing — his codebreaking work at Bletchley Park, his foundational contributions to computer science, and the persecution he faced for being gay — tying the whole experience back to both the historical "Ode to Turing" prompt and Pride Month.

Play it live: https://red-coder-27.github.io/solstice-cipher/

Video Demo

Code

https://github.com/red-coder-27/solstice-cipher

How I Built It

Solstice Cipher is a single self-contained HTML file — no build step, no backend, just vanilla JavaScript, CSS, and the Web Audio API, so it runs instantly in any browser with nothing to install.

I used Google Antigravity to generate the full initial build from a single detailed prompt covering the concept, all four cipher mechanics, the visual day-to-night theming, and the Turing Test ending. From there, I tested every level by hand-verifying the cipher math against the actual encryption logic, which caught a one-character bug in the Level 2 ciphertext that would have made that level mathematically unsolvable — a good reminder that AI-generated puzzle logic still needs to be checked against itself, not just read for plausibility.

A few design choices I'm happy with:

• The daylight timer bar literally shrinks faster on "even" in-game days, which makes the solstice's day-length asymmetry something you feel under time pressure rather than just read about.
• The Decrypt-O-Matic helper changes shape per cipher type (a shift slider for Caesar, fill-in-the-blank pairs for substitution, a tabbed lookup grid for Vigenère) so each level teaches its own cipher instead of reusing one generic input.
• The Turing Test ending has no timer and gives a score bonus regardless of how many you get right — it's meant as a reflective moment, not a fail state.

Prize Category

Submitting to both:

• Best Ode to Alan Turing — the entire back half of the game is a direct tribute: a literal Turing Test mechanic at the climax, followed by a factual dedication to his codebreaking legacy and his place in LGBTQIA+ history during Pride Month.
• Best Google AI Usage — the full game was built end-to-end using Google Antigravity from a single structured prompt, then debugged and polished afterward.