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Run npx skillmds@latest add yue-zhou1/vrf-auditor-2 in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

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Is Vrf Auditor free to use?

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Who published Vrf Auditor?

Yue-Zhou1 (@yue-zhou1) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Vrf Auditor by yue-zhou1 — Agent Skill

Name: Vrf Auditor
Author: Yue-Zhou1

Vrf Auditor

Audit Verifiable Random Function implementations (RFC 9381 ECVRF and RSA-FDH-VRF) for key validation, ciphersuite/suite-string domain separation, encode-to-curve and cofactor handling, proof-to-hash ordering, and uniqueness/pseudorandomness assumptions, plus application-level output grinding. Use when reviewing VRF provers, verifiers, or consumers of VRF outputs (leader election, lotteries, randomness beacons).

Yue-Zhou1 Updated Sep 17, 2026

File contents

vrf-auditor

Domain auditor for VRFs: proof generation, verification, and the trust rules consumers must follow before treating a VRF output as random.

When to Use

Auditing RFC 9381 ECVRF (any ciphersuite) or RSA-FDH-VRF provers and verifiers
Reviewing encode_to_curve/hash_to_curve usage, cofactor handling, and ciphersuite/suite-string domain separation
Reviewing proof_to_hash ordering and whether outputs are consumed before verification
Assessing uniqueness (full uniqueness vs trusted-key uniqueness), pseudorandomness assumptions, and application-level grinding resistance

When NOT to Use

VDF sequential-delay proofs (Wesolowski/Pietrzak) -> vdf-auditor
Ordinary signature scheme review without VRF output semantics -> signature-scheme-auditor
Elliptic-curve point validation/subgroup mechanics in isolation -> ecc-pairing-auditor
Nonce/CSPRNG generation mechanics -> randomness-auditor
Line-by-line RFC conformance diffing -> spec-delta-checker

Core Review Areas

Key validation: ECVRF public keys decoded and validated per the ciphersuite's validate_key rules (small-order/identity rejection for full uniqueness/collision resistance claims); RSA key sanity
Domain separation: suite string, DST, and challenge-generation separation octets exactly per RFC 9381; no cross-suite or cross-protocol hash reuse
encode_to_curve: correct method for the ciphersuite (TAI vs hash_to_curve per RFC 9380), including the salt and loop rules
Cofactor handling: Gamma multiplied by the cofactor in proof_to_hash; verification equation component checks
Nonce generation in proving: RFC 9381 §5.4.2 deterministic derivation (RFC 6979-style / RFC 8032-style) — reuse leaks the secret key
proof_to_hash ordering: beta computed only from a proof that verified; consumers must never use outputs before verify returns VALID
Uniqueness and pseudorandomness caveats: which property holds for adversarial keys under the chosen ciphersuite, and whether the application needs full uniqueness
Application grinding: can a participant re-key, re-input, or withhold outputs to bias the consuming protocol (leader election, lotteries)

Workflow

Phase 1: Construction and ciphersuite mapping

Read references/vrf-checklist.md
Pin the exact construction (ECVRF ciphersuite ID or RSA-FDH-VRF parameters) and the RFC 9381 sections that govern it

Phase 2: Prove/verify path review

Execute workflows/vrf-review.md

Phase 3: Pattern hunt

Read references/finding-patterns.md
Prioritize outputs used before verification, missing key validation, wrong cofactor handling, and grinding-by-withholding

Phase 4: Handoff

Send surviving findings to crypto-fp-check
Cross-route RFC conformance deltas to spec-delta-checker, EC point rules to ecc-pairing-auditor, and nonce generation to randomness-auditor

Output Contract

Produce a VRF handoff that includes:

vrf_family
prove_or_verify_path
uniqueness_or_pseudorandomness_invariant
evidence
disposition (one of verified, false_positive, unverified, observation, residual_risk)
next_route

Reference Index

references/vrf-checklist.md
references/finding-patterns.md
references/spec-sources.md
workflows/vrf-review.md

---name: vrf-auditor-2description: Audit Verifiable Random Function implementations (RFC 9381 ECVRF and RSA-FDH-VRF) for key validation, ciphersuite/suite-string domain separation, encode-to-curve and cofactor handling, proof-to-hash ordering, and uniqueness/pseudorandomness assumptions, plus application-level output grinding. Use when reviewing VRF provers, verifiers, or consumers of VRF outputs (leader election, lotteries, randomness beacons).---# vrf-auditorDomain auditor for VRFs: proof generation, verification, and the trustrules consumers must follow before treating a VRF output as random.## When to Use- Auditing RFC 9381 ECVRF (any ciphersuite) or RSA-FDH-VRF provers and verifiers- Reviewing encode_to_curve/hash_to_curve usage, cofactor handling, and ciphersuite/suite-string domain separation- Reviewing proof_to_hash ordering and whether outputs are consumed before verification- Assessing uniqueness (full uniqueness vs trusted-key uniqueness), pseudorandomness assumptions, and application-level grinding resistance## When NOT to Use- VDF sequential-delay proofs (Wesolowski/Pietrzak) -> `vdf-auditor`- Ordinary signature scheme review without VRF output semantics -> `signature-scheme-auditor`- Elliptic-curve point validation/subgroup mechanics in isolation -> `ecc-pairing-auditor`- Nonce/CSPRNG generation mechanics -> `randomness-auditor`- Line-by-line RFC conformance diffing -> `spec-delta-checker`## Core Review Areas1. Key validation: ECVRF public keys decoded and validated per the ciphersuite's validate_key rules (small-order/identity rejection for full uniqueness/collision resistance claims); RSA key sanity2. Domain separation: suite string, DST, and challenge-generation separation octets exactly per RFC 9381; no cross-suite or cross-protocol hash reuse3. encode_to_curve: correct method for the ciphersuite (TAI vs hash_to_curve per RFC 9380), including the salt and loop rules4. Cofactor handling: Gamma multiplied by the cofactor in proof_to_hash; verification equation component checks5. Nonce generation in proving: RFC 9381 §5.4.2 deterministic derivation (RFC 6979-style / RFC 8032-style) — reuse leaks the secret key6. proof_to_hash ordering: beta computed only from a proof that verified; consumers must never use outputs before verify returns VALID7. Uniqueness and pseudorandomness caveats: which property holds for adversarial keys under the chosen ciphersuite, and whether the application needs full uniqueness8. Application grinding: can a participant re-key, re-input, or withhold outputs to bias the consuming protocol (leader election, lotteries)## Workflow### Phase 1: Construction and ciphersuite mapping- Read `references/vrf-checklist.md`- Pin the exact construction (ECVRF ciphersuite ID or RSA-FDH-VRF parameters) and the RFC 9381 sections that govern it### Phase 2: Prove/verify path review- Execute `workflows/vrf-review.md`### Phase 3: Pattern hunt- Read `references/finding-patterns.md`- Prioritize outputs used before verification, missing key validation, wrong cofactor handling, and grinding-by-withholding### Phase 4: Handoff- Send surviving findings to `crypto-fp-check`- Cross-route RFC conformance deltas to `spec-delta-checker`, EC point rules to `ecc-pairing-auditor`, and nonce generation to `randomness-auditor`## Output ContractProduce a VRF handoff that includes:- `vrf_family`- `prove_or_verify_path`- `uniqueness_or_pseudorandomness_invariant`- `evidence`- `disposition` (one of `verified`, `false_positive`, `unverified`, `observation`, `residual_risk`)- `next_route`## Reference Index- [references/vrf-checklist.md](references/vrf-checklist.md)- [references/finding-patterns.md](references/finding-patterns.md)- [references/spec-sources.md](references/spec-sources.md)- [workflows/vrf-review.md](workflows/vrf-review.md)

Frequently asked questions