The Counting House

CACTF2026

Task: quantum-computing challenge over a Flask JSON API with three phases — forge an Aaronson-Christiano subspace-state note, read qubits prepared deterministically in Z or X, and beat a per-round basis-challenge seal. Solution: build ker(H_v) subspace states via GF(2) kernel + H/CX prep, brute-force the sha256 truncation convention, read bids in their deterministic basis, and answer the seal with Bell pairs that correlate in both bases.