Results from the Jane Street hardware puzzle

A small ASIC layout was revealed as a reverse‑engineering puzzle and turned out to be a hardware checker for an 11x11 Star Battle (Two Not Touch) puzzle. The chip accepts 121 input cycles - one bit per square - and runs parallel checks: 2‑bit counters for each row, column, and region (with a 121‑bit ROM mapping squares to regions), a delay line enforcing non‑adjacency (including diagonals), and a total‑star counter. The checks are ANDed to produce a success signal that unlocks an obfuscated ROM output string; on correct boards it prints "( TWO STARS )" one byte per clock, most incorrect boards yield "TRY AGAIN", and several Easter eggs and special outputs were embedded. The design used the SKY130 standard‑cell library and the LibreLane toolchain.

About 400 submissions from over 30 countries solved it using a wide range of techniques and tooling (KLayout, Yosys, Z3 and custom Python, Rust, C++, OCaml, Haskell and Odin code). Common approaches were GDS→netlist extraction (via LVS tools or custom parsers), Verilog or custom simulation (with pitfalls from mis‑modelled tie‑high cells), backward traversal from the success net guided by floorplan islands, dynamic impulse exploration of register responses, and SAT solving to produce valid input sequences. Solvers also reverse‑engineered the LFSR‑based obfuscation to read the ROM, produced striking visualizations, mapped the netlist to FPGA and Minecraft, ran analog SPICE checks, and even created a zero‑knowledge proof of a solution. Multiple intended Easter eggs were discovered, including hidden messages decoded from example VCD and layout marks.