Pqc Kem Auditor

pqc-kem-auditor

Domain auditor for concrete, standardized post-quantum KEMs. The current scope is ML-KEM (FIPS 203) only; other KEMs get added with their own primary sources and fixtures rather than by analogy.

Boundary with lattice-auditor: that skill owns generic LWE/RLWE parameter and noise-sampler reasoning (custom constructions, security estimates); this skill owns the standardized KEM's API, state, serialization, and decapsulation conformance.

When to Use

• Auditing ML-KEM-512/768/1024 (Kyber) encapsulation/decapsulation code
• Reviewing the Fujisaki-Okamoto transform implementation: re-encryption comparison and implicit rejection
• Reviewing ciphertext/public-key/secret-key encoding, modulus checks, and compression/rounding
• Assessing decapsulation-failure oracles and constant-time reject paths
• Checking parameter-set and spec-version provenance (FIPS 203 final vs draft vs round-3 Kyber)

When NOT to Use

• Generic LWE/RLWE parameter soundness, custom lattice schemes, noise sampling design -> lattice-auditor
• Post-quantum signatures (ML-DSA, SLH-DSA, Falcon, XMSS/LMS) -> the lattice/PQ signature review path
• Classical KEM/hybrid TLS integration questions -> encryption-scheme-auditor for the symmetric side plus this skill for the KEM side
• Timing leakage measurement methodology -> side-channel-auditor

Core Review Areas

1. Version/parameter provenance: FIPS 203 final vs CRYSTALS-Kyber round-3 differences (domain separation of K derivation, hash choices); the parameter set (512/768/1024) matches the claimed category
2. Input validation: public-key modulus check (encoded coefficients < q), ciphertext length/type checks, secret-key hash consistency (FIPS 203 §7.2/§7.3 input checking)
3. Encapsulation: m sampled from an approved RBG, K derived exactly per spec, no K exposure before ciphertext output
4. Decapsulation and implicit rejection: re-encrypt and compare; on mismatch return K-bar = J(z || c) with NO observable difference from success (no error return, no timing/branch difference, no logging)
5. Compression/rounding: Compress/Decompress rounding per spec; off-by-one rounding changes failure probability and interop
6. Failure-oracle resistance: nothing (timing, errors, retries, metrics) distinguishes implicit rejection from success across many queries
7. State and key lifecycle: z randomness quality, secret-key zeroization, no seed reuse across keypairs

Workflow

Phase 1: Version and parameter mapping

• Read references/pqc-kem-checklist.md
• Pin the spec version and parameter sets; queue spec-delta-checker if the code claims FIPS 203 conformance

Phase 2: Decapsulation review

• Execute workflows/kem-decapsulation-review.md

Phase 3: Pattern hunt

• Read references/finding-patterns.md
• Prioritize explicit-failure decapsulation, missing modulus checks, and round-3/FIPS derivation mixing

Phase 4: Handoff

• Send surviving findings to crypto-fp-check
• Cross-route parameter/noise design questions to lattice-auditor and timing measurement to side-channel-auditor

Output Contract

Produce a KEM handoff that includes:

• kem_family_and_parameter_set
• encapsulation_or_decapsulation_path
• failure_oracle_invariant
• evidence
• disposition (one of verified, false_positive, unverified, observation, residual_risk)
• next_route

Reference Index

• references/pqc-kem-checklist.md
• references/finding-patterns.md
• references/spec-sources.md
• workflows/kem-decapsulation-review.md