echo.ls

Who this is

A blog, and the winner Zden's catalogue links to. The blog has no name on it, just posts. So the record calls the solver what the site calls itself.

Level 5 went up in October 2018 and sat there. In 2021 Zden admitted the first image was incomplete and put up a fixed one. Even then it took almost five more years. On September 22, 2026 the prize moved. Five days later the write-up landed.

How it went

Sixty four rectangles and a tiny diagram with -1, ×10 and 64. The trick was finding the formula the diagram hints at. Ten times the side, plus the border, minus one, over 64. The write-up says the formula was found by experiment, with GPT-6 Astra helping on quick prototypes. Fair enough. Zden's own hint did the rest: sum the areas in pairs and every pair is a byte.

Why does a solver page for one puzzle matter? Because it closes the longest wait in the collection. And it shows the work. The post ends by saying the puzzle only seems simple in retrospect. That's the most honest line a solver can write.

What the record says

Four facts. Three come from the write-up: the key with the method, the solve date and the AI help. The fourth is Zden's catalogue calling it the winner's post. The key itself is on the puzzle record, and puzzles verify zden/level-5 checks it against the address.

The record

solver: party("echo.ls", {
  key: "echo-ls",
  kind: PartyKind.Person,
  about: "Author of the echo.ls blog, who solved Zden's corrected Level 5 and published the key with the method.",
  profiles: [profile("website", "https://echo.ls/")],
  facts: [
    fact("Published the private key and the method: each rectangle's area after the transform the corner diagram suggests, summed in pairs into the 32 key bytes.", SOLUTION, { date: "2026-09-27" }),
    fact("Wrote that they solved the corrected puzzle on September 22, 2026.", SOLUTION, { date: "2026-09-27" }),
    fact("Wrote that they used GPT-6 Astra for quick prototyping and experimentation.", SOLUTION, { date: "2026-09-27" }),
    fact("Zden's catalog links the write-up as the solution written by the winner.", "https://crypto.haluska.sk/"),
  ],
}),