lib-q-hqc

Post-quantum HQC (Hamming Quasi-Cyclic) KEM implementation for libQ.

Enable from the KEM façade with hqc on lib-q-kem.

Overview

Pure-Rust HQC KEM for parameter sets HQC-128, HQC-192, and HQC-256 (internal names HQC-1, HQC-3, HQC-5). The crate follows libQ provider patterns, supports no_std and WASM, and offers optional AVX2 acceleration with portable fallback.

Implementation status

Not production-ready. Core modules (Reed–Solomon, Reed–Muller, concatenated code, PKE, KEM, SHAKE256 PRNG) are implemented and covered by tests. Randomized encrypt/decrypt and encapsulate/decapsulate round-trips are verified across all parameter sets (portable and AVX2 paths). Remaining blockers are full NIST KEM KAT conformance and independent side-channel evaluation — see docs/audit-package/README.md for verified facts and open findings. Do not deploy for confidentiality guarantees until those findings are closed.

Security levels

Object sizes match lib-q-types::hqc (workspace source of truth for wire lengths):

Algorithm	Security	Public key	Secret key	Ciphertext	Shared secret
HQC-128	128 bits	2,241 B	2,337 B	4,433 B	32 B
HQC-192	192 bits	4,522 B	4,618 B	8,978 B	32 B
HQC-256	256 bits	7,245 B	7,341 B	14,421 B	32 B

Secret key layout: ek_pke ‖ dk_pke (32) ‖ sigma (16) ‖ seed_kem (48).

Features

Three parameter sets: hqc128, hqc192, hqc256 (or hqc for all)
libQ provider integration and typed key/ciphertext wrappers
zeroize for sensitive buffers; no_std and wasm targets
Pure Rust (no C/FFI); BearSSL-compatible and standard AES DRBG backends
Optional simd-avx2 (runtime detection, bit-exact portable fallback)

Architecture

Module	Role
`hqc_kem`	KEM encapsulation / decapsulation
`hqc_pke`	Public-key encryption layer
`params_correct`	Parameter sets HQC-1 / HQC-3 / HQC-5
`concatenated_code`	Reed–Solomon + Reed–Muller concatenated code
`reed_solomon`, `reed_muller`	Constituent codes
`internal`	Polynomial / vector primitives, SHAKE256
`provider`	libQ KEM provider

Optional KAT DRBG backends (not enabled by default): kat-drbg / bearssl-aes (reference-compatible) and aes-drbg (pure Rust NIST CTR_DRBG). Production RNG uses lib-q-random via the random feature.

See SIMD architecture and vector operations.

Usage

use lib_q_random::LibQRng;
use lib_q_hqc::hqc_core_impl::*;

let mut rng = LibQRng::new_deterministic([42u8; 32]);
let keypair = Hqc128CoreImpl::generate_keypair(&mut rng);

let (ciphertext, shared_secret1) = Hqc128CoreImpl::encapsulate(&keypair.public_key, &mut rng)
    .expect("encapsulation");
let shared_secret2 = Hqc128CoreImpl::decapsulate(&keypair.secret_key, &ciphertext)
    .expect("decapsulation");

assert_eq!(shared_secret1.as_slice(), shared_secret2.as_slice());

Integration tests exercise KEM round-trips with both pinned seeds (for reproducible shared-secret comparison) and many varied keypairs across all parameter sets (test_kem_roundtrip_varied_keys_all_params).

Testing

cargo test -p lib-q-hqc --features alloc,hqc
cargo test -p lib-q-hqc --test integration_test --features alloc,hqc128
cargo test -p lib-q-hqc --features "simd-avx2,alloc,hqc128" --test simd_correctness

See tests/README.md for the test layout. Diagnostic and historical debug tests live under tests/archive/.

SIMD (AVX2)

cargo build --release -p lib-q-hqc --features simd-avx2
cargo bench -p lib-q-hqc --features "simd-avx2,alloc,hqc128" --bench simd_benchmarks

Requires x86_64 with AVX2; falls back to portable code when unavailable.

Known limitations

Documented in SECURITY.md and docs/audit-package/README.md:

No independent side-channel evaluation; constant-time discipline in source only.
Full NIST KEM KAT conformance is not yet established by a non-ignored test suite.

Security

See SECURITY.md. Report vulnerabilities via the workspace SECURITY.md policy.

License

Same terms as the main libQ workspace.

lib-q-hqc 0.0.6