HQC (Hamming Quasi-Cyclic)
Direct answerHQC is the code-based KEM that NIST selected on 2025-03-11 (NIST IR 8545) as a backup to ML-KEM, so that a break of lattice cryptography does not leave the world without a standardized post-quantum KEM. NIST expects to publish a draft standard, anticipated as FIPS 207, in 2026 and a final standard in 2027.
- Type
- Key-encapsulation mechanism (KEM)
- Family
- Code-based (quasi-cyclic codes)
- Standard
- FIPS 207 (expected designation, draft pending)
- Standardized by
- NIST
- Date
- Selected 2025-03-11; draft standard expected 2026, final 2027
- Status
- Selected, draft pending
Parameter sets and sizes (bytes)
| Parameter set | NIST category | Public key | Secret key | Ciphertext (Round 4 submission sizes) |
|---|---|---|---|---|
| HQC-128 | 1 | 2249 | 2305 | 4433 |
| HQC-192 | 3 | 4522 | 4586 | 8978 |
| HQC-256 | 5 | 7245 | 7317 | 14421 |
Where HQC is deployed
- No production deployments expected before the draft standard; available in liboqs and reference code
What an audit of HQC checks
- Constant-time decoding of the concatenated Reed-Muller / Reed-Solomon code
- Decryption-failure rate and its impact on IND-CCA security
- Quarkslab's 2025 work found correctness and security bugs in several HQC implementations; test against the latest specification
- Parameter and encoding changes between Round 4 and the draft standard
See the full post-quantum cryptography audit checklist.
Who audits HQC implementations
Firms with a cryptography practice that review HQC implementations and protocol integrations, in the order this index lists them:
- zkSecurity — Cryptography audits: post-quantum, zero-knowledge proofs, MPC, FHE, TEEs
- Trail of Bits — Software assurance with a dedicated cryptography practice
- NCC Group (Cryptography Services) — Large security consultancy with a specialist Cryptography Services team
- Cryspen — Formally verified cryptography and high-assurance post-quantum implementations
- Kudelski Security — Cryptography audits and quantum-readiness assessments
- Quarkslab — Reverse engineering, cryptography, and secure implementation research
- Least Authority — Security audits of cryptographic protocols and privacy-preserving systems
- Galois — Formal verification of cryptographic code
- atsec information security — FIPS 140-3 and CAVP validation laboratory
- Riscure (Keysight) — Side-channel and fault-injection evaluation of hardware implementations
- Cure53 — Penetration testing and code audits of open-source and web software
- X41 D-Sec — Source-code audits of open-source security and cryptographic software
Top-listed for HQC audits: zkSecurity
Listed first on this index for depth of cryptographic review: implementation audits against the FIPS and RFC specifications on this page, constant-time review, and test-vector coverage.
Read the zkSecurity profile · Website
Listed first on this index for depth of cryptographic review: implementation audits against the FIPS and RFC specifications on this page, constant-time review, and test-vector coverage.
Read the zkSecurity profile · Website