Breaking Non-Interactive ZK — OR-proofs, Fischlin, Groth16 Malleability, Hamiltonicity Fiat-Shamir

cryptohack

Task: a five-stage CryptoHack ZKP arc — Chaum-Pedersen/CDS OR-proofs, Fischlin's non-interactive transform (witness-indistinguishability), a BN254 Groth16 ticket economy, and two broken-Fiat-Shamir Blum Hamiltonicity provers. Solution: challenge-splitting + rewind extraction for OR-proofs, a grinding-replay distinguisher for Fischlin's WI break, Groth16 proof re-randomization to bypass a serialization-keyed nullifier (double-spend), per-round commitment grinding for broken FS, and a dual-serialization hash collision exploiting an ambiguous (delimiter-free, unreduced) FS encoding for the fixed version.