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Key Encapsulation

Classic McEliece

Classic McEliece Code-Based KEM

non-FIPScode-based1 parameter setsQNSP tier: maximum+provider: liboqsalso called: McEliece, Niederreiter
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.

Mechanism

How it works

Classic McEliece uses binary Goppa codes. The public key is a permuted, scrambled generator matrix; the secret key is the underlying Goppa code structure. Encryption adds error vectors to a codeword; decryption uses Patterson's algorithm to correct the errors. Security has been studied continuously for 47+ years with no major breaks.

Parameter Sets

1 variants shipped

Each variant trades security category against key, ciphertext, or signature size. QNSP exposes all variants via the @cuilabs/liboqs-native binding; tenant crypto-policy determines which are allowed.

VariantNIST LevelPublic KeySecret KeyCiphertextNote
mceliece348864 / 460896 / 6688128 / 6960119 / 8192128L5261,120 B6,452 B96 B5 parameter sets covering NIST security categories 1, 3, and 5. Public keys range 261 KB – 1.36 MB.

NIST ACVP

Conformance evidence

QNSP runs the official NIST ACVP test vectors against every shipped algorithm. Live evidence + SHA-3-256 tamper digest at /verify/conformance.

@noble/post-quantum
non-addressable
Pure-JavaScript reference; cross-verification secondary on Maximum + Government tiers.
@cuilabs/liboqs-native
non-addressable
Native-C primary production engine. Runs across every QNSP backend service.
View live ACVP evidence →

Use Cases

When to use it

  • Highest-assurance workloads where conservative assumption value outweighs key-size cost
  • Stable long-term keys where the one-time public-key bandwidth is acceptable (private CA keys, root signing identities)

Trade-offs

What you give up, what you get

  • Public keys are 100x-1000x larger than ML-KEM-1024 — fundamentally not suitable for TLS or per-session usage
  • Smallest ciphertexts in the PQC catalogue (96-240 bytes)
  • Best-studied PQC security assumption (47+ years of cryptanalysis)

FAQ

Classic McEliece — frequently asked questions

Concise, source-of-truth answers to the questions buyers and engineers ask most about this algorithm.

What is Classic McEliece?

Classic McEliece (Classic McEliece Code-Based KEM) is a code based post-quantum key encapsulation mechanism. It is designed to resist attacks from both classical and quantum computers, and QNSP ships 1 of its parameter sets. It is also known as McEliece, Niederreiter.

Is Classic McEliece NIST-standardized?

Classic McEliece is not a finalized NIST FIPS standard. QNSP ships it as a non-FIPS post-quantum option, typically to add an independent cryptographic assumption (code based) alongside the FIPS-standardized ML-KEM and ML-DSA for defence-in-depth.

What is Classic McEliece used for?

On QNSP, Classic McEliece is used for Highest-assurance workloads where conservative assumption value outweighs key-size cost; Stable long-term keys where the one-time public-key bandwidth is acceptable (private CA keys, root signing identities). It is available from the maximum crypto-policy tier upward via the liboqs provider.

References

Primary sources