HQC
acronymcryptography
Stands for: Hamming Quasi-Cyclic
A code-based post-quantum key-encapsulation algorithm selected by NIST as a backup.
Hamming Quasi-Cyclic is a code-based key-encapsulation mechanism NIST selected in 2025 as a backup to the lattice-based ML-KEM, so that post-quantum security does not rest on a single mathematical assumption.
HQC is a code-based key encapsulation mechanism selected by NIST as a backup to ML-KEM. Its purpose is diversity: ML-KEM rests on lattice problems, and standardizing a second algorithm resting on a different mathematical foundation means a breakthrough against one does not leave the world without an option.
That reasoning is worth understanding because it is unusual. Normally standards bodies pick the best candidate and stop; here the risk being managed is that post-quantum assumptions are younger and less attacked than RSA's were, so hedging across families is prudent rather than indecisive. HQC has larger keys and ciphertexts than ML-KEM, which is why it is the reserve rather than the default.
Also known as: hqc