signet::forge::crypto::HybridKem Class Reference

Hybrid Key Encapsulation combining Kyber-768 (post-quantum) and X25519 (classical). More...

#include <post_quantum.hpp>

Classes
struct	HybridEncapsResult
	Result of hybrid encapsulation. More...
struct	HybridKeyPair
	Hybrid keypair: Kyber-768 + X25519 components. More...

Static Public Member Functions
static expected< HybridKeyPair >	generate_keypair ()
	Generate a hybrid Kyber-768 + X25519 (RFC 7748) keypair.
static expected< HybridEncapsResult >	encapsulate (const HybridKeyPair &recipient_pk)
	Hybrid encapsulation: Kyber-768 + X25519 DH key agreement.
static expected< std::vector< uint8_t > >	decapsulate (const HybridEncapsResult &encaps, const HybridKeyPair &recipient_sk)
	Hybrid decapsulation: recovers the same shared secret as encapsulate().

Static Public Attributes
static constexpr size_t	X25519_PUBLIC_KEY_SIZE = 32
	X25519 public key size in bytes.
static constexpr size_t	X25519_SECRET_KEY_SIZE = 32
	X25519 secret key size in bytes.
static constexpr size_t	HYBRID_SHARED_SECRET_SIZE = 32
	Combined shared secret size (SHA-256 output).

Detailed Description

Hybrid Key Encapsulation combining Kyber-768 (post-quantum) and X25519 (classical).

The shared secret is derived as SHA-256(kyber_ss || x25519_ss), providing defense-in-depth: even if one algorithm is broken, the other still provides security. Follows the NIST/IETF Composite KEM approach.

X25519 uses the real constant-time Montgomery ladder in detail::x25519 (RFC 7748) in both bundled and liboqs modes.

See also

KyberKem for standalone Kyber-768

DilithiumSign for post-quantum signatures

Definition at line 1339 of file post_quantum.hpp.

Member Function Documentation

decapsulate()

static expected< std::vector< uint8_t > > signet::forge::crypto::HybridKem::decapsulate ( const HybridEncapsResult &  encaps, const HybridKeyPair &  recipient_sk  )

inlinestatic

Hybrid decapsulation: recovers the same shared secret as encapsulate().

X25519 DH is commutative: X25519(eph_sk, recip_pk) == X25519(recip_sk, eph_pk).

Parameters

encaps	Encapsulation result (ciphertext + ephemeral pk).
recipient_sk	Recipient's full hybrid keypair (secret keys used).

Returns

32-byte combined shared secret, identical to encapsulate()'s output.

Definition at line 1483 of file post_quantum.hpp.

encapsulate()

static expected< HybridEncapsResult > signet::forge::crypto::HybridKem::encapsulate ( const HybridKeyPair &  recipient_pk )

inlinestatic

Hybrid encapsulation: Kyber-768 + X25519 DH key agreement.

Parameters

recipient_pk

Recipient's hybrid keypair (only public keys used).

Returns

Kyber ciphertext + ephemeral X25519 pk + combined shared secret.

Definition at line 1418 of file post_quantum.hpp.

generate_keypair()

static expected< HybridKeyPair > signet::forge::crypto::HybridKem::generate_keypair ( )

inlinestatic

Generate a hybrid Kyber-768 + X25519 (RFC 7748) keypair.

Returns

HybridKeyPair with all four key components, or an error on failure.

Definition at line 1378 of file post_quantum.hpp.

Member Data Documentation

HYBRID_SHARED_SECRET_SIZE

constexpr size_t signet::forge::crypto::HybridKem::HYBRID_SHARED_SECRET_SIZE = 32

staticconstexpr

Combined shared secret size (SHA-256 output).

Definition at line 1343 of file post_quantum.hpp.

X25519_PUBLIC_KEY_SIZE

constexpr size_t signet::forge::crypto::HybridKem::X25519_PUBLIC_KEY_SIZE = 32

staticconstexpr

X25519 public key size in bytes.

Definition at line 1341 of file post_quantum.hpp.

X25519_SECRET_KEY_SIZE

constexpr size_t signet::forge::crypto::HybridKem::X25519_SECRET_KEY_SIZE = 32

staticconstexpr

X25519 secret key size in bytes.

Definition at line 1342 of file post_quantum.hpp.

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The documentation for this class was generated from the following file:

• include/signet/crypto/post_quantum.hpp