Algorithms
What is Classic McEliece?
Code-based KEM from a 1978 cryptosystem with the longest cryptanalytic track record of any NIST candidate. Very large public keys (~261 KB at level 5) but very small ciphertexts (~96 bytes). NIST Round 4 finalist; QNSI supports it for HNDL-conservative deployments.
Decision context
Why Classic McEliece matters
Classic McEliece provides a long-studied code-based KEM design and mathematical diversity from ML-KEM. Its unusually large public keys change certificate, handshake, directory, firmware, memory, and network assumptions, so adoption is an architectural decision rather than a simple algorithm toggle.
How to evaluate Classic McEliece
Measure public-key distribution, storage, handshake size, memory use and latency in the intended environment. Verify the exact parameter set and provider with authoritative vectors and invalid-ciphertext tests. Confirm that every protocol field and intermediary can carry the resulting objects without truncation or silent fallback.
Algorithms
Algorithms evidence boundary
Algorithm names alone do not establish security or deployment readiness. Parameter set, implementation, key and signature sizes, execution boundary, validation status, and failure behaviour all matter. Buyers should distinguish a standardized primitive from a product path that has independently demonstrated that primitive in production.
Deep dive
Classic McEliece on QNSI
The original code-based public-key cryptosystem, in continuous study since 1978 - by far the oldest cryptographic assumption in the PQC catalogue. Trades extremely large public keys for the most-studied security assumption available.
For parameter sets, key and signature sizes, NIST ACVP conformance status, and when to use it, see the full Classic McEliece algorithm reference.
FAQ
Common questions
What is Classic McEliece?
Code-based KEM from a 1978 cryptosystem with the longest cryptanalytic track record of any NIST candidate. Very large public keys (~261 KB at level 5) but very small ciphertexts (~96 bytes). NIST Round 4 finalist; QNSI supports it for HNDL-conservative deployments.
Why does Classic McEliece matter?
Classic McEliece provides a long-studied code-based KEM design and mathematical diversity from ML-KEM. Its unusually large public keys change certificate, handshake, directory, firmware, memory, and network assumptions, so adoption is an architectural decision rather than a simple algorithm toggle.
How should Classic McEliece be evaluated?
Measure public-key distribution, storage, handshake size, memory use and latency in the intended environment. Verify the exact parameter set and provider with authoritative vectors and invalid-ciphertext tests. Confirm that every protocol field and intermediary can carry the resulting objects without truncation or silent fallback.
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