Struct ClassicMcEliece 

pub struct ClassicMcEliece { /* private fields */ }

Classic McEliece 8192128f (security level 5, fast key-generation variant).

Classic McEliece is a code-based KEM with over 50 years of cryptanalytic history behind its underlying hard problem (decoding random binary Goppa codes). It is one of the most conservative choices available in post-quantum cryptography.

The f (fast) variant uses a different key-generation algorithm that is significantly faster at the cost of slightly larger public keys compared to the standard variant; the ciphertext size and security level are unchanged.

Sizes

Object	Bytes
Public key	1,357,824
Secret key	14,120
Ciphertext	208
Shared secret	32

Pros

• Based on coding theory, an entirely different mathematical family from lattice schemes. Serves as a strong hedge in hybrid constructions.
• ~50 years of cryptanalysis with no fundamental structural breaks.
• Tiny ciphertext (208 B) — ideal when the encapsulated ciphertext must be transmitted repeatedly but the public key can be stored once (e.g. in a certificate or a static configuration file).
• Extremely fast encapsulation and decapsulation, even faster than RSA.

Cons

• Very large public key (~1.3 MB) — prohibitive for protocols that transmit the public key in every session (e.g. standard TLS handshakes). Plan for out-of-band distribution or long-lived public keys.
• Key generation is slow even with the f variant; not suitable for ephemeral key exchange patterns where a fresh keypair is needed per session.

Reuse

Construct once with ClassicMcEliece::new and reuse across operations — each instance owns the underlying liboqs algorithm object, so reusing it avoids re-allocating that object on every encapsulation/decapsulation. This matters most in a tight handshake loop where a responder decapsulates with the same static key repeatedly.

Implementations

impl ClassicMcEliece

pub const PUBLIC_KEY_LEN: usize = 1_357_824

Length in bytes of a serialized public key.

pub const SECRET_KEY_LEN: usize = 14_120

Length in bytes of a serialized secret key.

pub const CIPHERTEXT_LEN: usize = 208

Length in bytes of a ciphertext.

pub const SHARED_SECRET_LEN: usize = 32

Length in bytes of the encapsulated shared secret.

pub fn new() -> Self

Construct a reusable Classic McEliece 8192128f instance.

Infallible: Classic McEliece 8192128f is always compiled in via the crate’s oqs feature set, so the underlying algorithm object can always be created.

pub fn keypair(&self) -> Result<(PublicKey, SecretKey)>

pub fn encapsulate( &self, public_key: &PublicKey, ) -> Result<(Ciphertext, SharedSecret)>

pub fn decapsulate( &self, secret_key: &SecretKey, ciphertext: &Ciphertext, ) -> Result<SharedSecret>

pub fn ciphertext_from_bytes(&self, bytes: &[u8]) -> Result<Ciphertext>

Reconstruct a ciphertext from its serialized bytes.

Returns Error::InvalidLength if bytes is not exactly CIPHERTEXT_LEN bytes long.

pub fn public_key_from_bytes(&self, bytes: &[u8]) -> Result<PublicKey>

Reconstruct a public key from its serialized bytes.

Returns Error::InvalidLength if bytes is not exactly PUBLIC_KEY_LEN bytes long.

pub fn secret_key_from_bytes(&self, bytes: &[u8]) -> Result<SecretKey>

Reconstruct a secret key from its serialized bytes.

Returns Error::InvalidLength if bytes is not exactly SECRET_KEY_LEN bytes long.

Trait Implementations

impl Default for ClassicMcEliece

fn default() -> Self

Returns the “default value” for a type.