Behavior-Bound Signatures: Policy Compliance via Zero-Knowledge Soundness

We introduce behavior-bound signatures (BBS), a signature framework in which Verify accepts if and only if a zero-knowledge proof establishes that the signer's action satisfies a prescribed policy predicate. Unlike traditional signatures—whose acceptance depends on identity alone—BBS makes compliance a cryptographic invariant enforced at the verification gate, rather than by external monitoring or honest-majority assumptions. We formalize policy-soundness under chosen-message attacks (PS-CMA), extending EUF-CMA by requiring that no adversary can produce a valid signature for any action violating the policy, and prove that BBS achieves PS-CMA security under standard assumptions (Pedersen binding, Poseidon collision resistance, Bulletproofs/PLONK soundness). The action input is deterministically bound to an external commitment, preventing the signer from grinding compliant inputs. We show that the resulting acceptance predicate rejects all non-compliant proposals regardless of adversarial majority—decoupling compliance safety from honest-quorum requirements. Verification is local and O(1) per proposal; no quorum is needed to enforce the policy.