Privacy Protocol Auditor

privacy-protocol-auditor

Domain auditor for the protocol layer of privacy systems (shielded pools, mixers, private transfer protocols): the rules that connect commitments, nullifiers, Merkle roots, and on-chain state into a double-spend-free, unlinkable system.

When to Use

• Auditing nullifier derivation, uniqueness, domain separation, and spent-set semantics
• Reviewing note/value commitments and their binding to ownership keys
• Reviewing deposit/withdraw flows, relayer roles, and front-running behavior
• Reviewing shielded-pool state transitions, join-splits, change-output linkage, and replay domains (forks, multiple pools, protocol versions)

When NOT to Use

• Circuit constraint completeness of the proof itself -> zk-circuit-auditor
• Merkle tree mechanics (insertion, inclusion proofs, sparse defaults) -> merkle-tree-auditor
• Verifier-contract precompile/calldata mechanics -> onchain-verifier-auditor
• Commitment-scheme mathematics (Pedersen binding/hiding) -> commitment-scheme-auditor

Core Review Areas

1. Nullifier derivation: computed from the note secret AND position/rho so each note has exactly one nullifier; domain-separated per pool, asset, chain, and protocol version
2. Spent-set semantics: nullifier recorded before external calls; checked against the same tree/root domain the proof was verified for
3. Commitment binding: note commitments bind owner key, value, randomness; ownership proof required to spend (not just knowledge of the commitment)
4. Root management: which historical roots are accepted, root freshness windows, and cross-root replay
5. Deposit/withdraw flow: front-running of deposits/withdrawals, relayer fee binding inside the proof statement, recipient binding
6. State transitions: join-split value conservation at the protocol level, change-output linkage/unlinkability, migration paths between pool versions

Workflow

Phase 1: Protocol state mapping

• Read references/privacy-protocol-checklist.md
• Map the state machine: commitments in, nullifiers out, roots accepted, and every state-mutating entry point

Phase 2: Nullifier and transition review

• Execute workflows/nullifier-review.md

Phase 3: Pattern hunt

• Read references/finding-patterns.md
• Prioritize nullifier collisions/aliasing, cross-domain replay, unbound relayer/recipient fields, and root acceptance gaps

Phase 4: Handoff

• Send surviving findings to crypto-fp-check
• Cross-route constraint suspicions to zk-circuit-auditor, tree mechanics to merkle-tree-auditor, and verifier-call mechanics to onchain-verifier-auditor

Output Contract

Produce a privacy-protocol handoff that includes:

• protocol_state_transition
• nullifier_or_commitment_invariant
• privacy_or_replay_impact
• evidence
• disposition (one of verified, false_positive, unverified, observation, residual_risk)
• next_route

Reference Index

• references/privacy-protocol-checklist.md
• references/finding-patterns.md
• references/spec-sources.md
• workflows/nullifier-review.md