The Coin That Wont Land

CACTF2026

Task: quantum bit-commitment (Oathbinding) game exposed over an HTTP JSON API; the committer keeps qubit a while the Warden seals qubit b, and must survive 32 rounds with a per-round challenge basis (2^-32 by luck). Solution: EPR/Bell-state cheat — commit Phi+ entangled pairs, then peek the kept qubit in the challenged basis and open with those outcomes, exploiting the no-go theorem that quantum bit commitment cannot be both binding and hiding.