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Threshold ecdsa auditor

Skill Yue-Zhou1/zkcrypto-audit/plugins/protocol-auditors/skills/threshold-ecdsa-auditor

Audit threshold ECDSA implementations (GG18, GG20, CGGMP21, Lindell-style) for Paillier modulus validity, MtA/MtAwc range-proof gaps, share-conversion soundness, resharing and concurrent-session isolation, and identifiable-abort leakage. Use when reviewing multi-party ECDSA keygen, signing, or resharing.From its SKILL.md

Install
npx -y skills add Yue-Zhou1/zkcrypto-audit --skill threshold-ecdsa-auditor

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SKILL.md

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threshold-ecdsa-auditor

Domain auditor for multi-party ECDSA: protocols that split an ECDSA key across parties and sign via Paillier-based or OT-based share conversion (GG18, GG20, CGGMP21, Lindell 2P-ECDSA and descendants).

When to Use

  • Auditing GG18/GG20/CGGMP21/Lindell-style keygen, signing, or resharing
  • Reviewing Paillier modulus generation and validity (square-free, no-small-factor) proofs
  • Reviewing MtA/MtAwc range and consistency proofs and share conversions
  • Reviewing presignature handling, concurrent signing sessions, and identifiable-abort behavior

When NOT to Use

  • FROST, MuSig2, threshold Schnorr, or generic DKG/VSS review -> dkg-threshold-auditor
  • Generic OT, garbled circuits, or share-MAC (SPDZ-style) review -> mpc-auditor
  • Single-party ECDSA signing in an Ethereum application (ecrecover, EIP-712, alloy/ethers-rs) -> ethereum-crypto-auditor
  • Generic single-party signature scheme review (verification equations, malleability, encodings) -> signature-scheme-auditor
  • Nonce/CSPRNG generation mechanics -> randomness-auditor
  • Timing/cache leakage of share arithmetic -> side-channel-auditor

Core Review Areas

  1. Paillier modulus N: generation, biprimality/square-free proof, and no-small-factor proof actually verified by every counterparty
  2. MtA/MtAwc: range proofs present AND verified on both directions of the conversion; missing range proofs enable the classic key-extraction attacks (Alpha-Rays class)
  3. Share conversion algebra: additive/multiplicative conversion consistency, Lagrange coefficient handling, and modulus mixing (mod N vs mod q)
  4. Key generation: commitment-then-reveal ordering, feldman VSS checks, rogue-key resistance
  5. Signing sessions: presignature single-use, concurrent-session state isolation, nonce contribution binding (k-share vs gamma-share)
  6. Resharing: old-committee/new-committee authorization and share zeroization
  7. Identifiable abort: blame paths must not leak share or nonce information (GG20 identifiable abort vs CGGMP21 accountability)

Workflow

Phase 1: Protocol and version mapping

  • Read references/threshold-ecdsa-checklist.md
  • Identify the exact construction and paper version (GG18 vs GG20 vs CGGMP21 revision) — checks differ per construction
  • Map rounds to code: keygen, presign/sign, reshare entry points

Phase 2: Paillier and MtA review

  • Execute workflows/mta-review.md
  • Verify modulus validity proofs and both MtA directions' range proofs

Phase 3: Pattern hunt

  • Read references/finding-patterns.md
  • Prioritize missing range-proof verification, presignature reuse, concurrent-session nonce leakage, and abort-path oracles

Phase 4: Handoff

  • Send surviving findings to crypto-fp-check
  • Cross-route generic MPC building blocks to mpc-auditor, RNG concerns to randomness-auditor, and leakage concerns to side-channel-auditor

Output Contract

Produce a threshold-ECDSA handoff that includes:

  • protocol_round
  • proof_or_range_check
  • invariant_at_risk
  • evidence
  • disposition (one of verified, false_positive, unverified, observation, residual_risk)
  • next_route

Reference Index

What ships with it: 5 files

10.7 KB alongside SKILL.md

agents/

references/

workflows/

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