xref: /openbsd/lib/libcrypto/mlkem/mlkem.h (revision ef1019e6)

/*	$OpenBSD: mlkem.h,v 1.4 2024/12/19 23:52:26 tb Exp $ */
/*
 * Copyright (c) 2024, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#ifndef OPENSSL_HEADER_MLKEM_H
#define OPENSSL_HEADER_MLKEM_H

#include <sys/types.h>
#include <stdint.h>

#if defined(__cplusplus)
extern "C" {
#endif

/* Hack for now */
struct cbs_st;
struct cbb_st;

/*
 * ML-KEM-768
 *
 * This implements the Module-Lattice-Based Key-Encapsulation Mechanism from
 * https://csrc.nist.gov/pubs/fips/204/final
 */

/*
 * MLKEM768_public_key contains a ML-KEM-768 public key. The contents of this
 * object should never leave the address space since the format is unstable.
 */
struct MLKEM768_public_key {
	union {
		uint8_t bytes[512 * (3 + 9) + 32 + 32];
		uint16_t alignment;
	} opaque;
};

/*
 * MLKEM768_private_key contains a ML-KEM-768 private key. The contents of this
 * object should never leave the address space since the format is unstable.
 */
struct MLKEM768_private_key {
	union {
		uint8_t bytes[512 * (3 + 3 + 9) + 32 + 32 + 32];
		uint16_t alignment;
	} opaque;
};

/*
 * MLKEM768_PUBLIC_KEY_BYTES is the number of bytes in an encoded ML-KEM768 public
 * key.
 */
#define MLKEM768_PUBLIC_KEY_BYTES 1184

/* MLKEM_SEED_BYTES is the number of bytes in an ML-KEM seed. */
#define MLKEM_SEED_BYTES 64

/*
 *  MLKEM_SHARED_SECRET_BYTES is the number of bytes in the ML-KEM768 shared
 * secret. Although the round-3 specification has a variable-length output, the
 * final ML-KEM construction is expected to use a fixed 32-byte output. To
 * simplify the future transition, we apply the same restriction.
 */
#define MLKEM_SHARED_SECRET_BYTES 32

/*
 * MLKEM_generate_key generates a random public/private key pair, writes the
 * encoded public key to |out_encoded_public_key| and sets |out_private_key| to
 * the private key. If |optional_out_seed| us not NULL then te seed used to
 * generate te private key is written to it.
 */
void MLKEM768_generate_key(
    uint8_t out_encoded_public_key[MLKEM768_PUBLIC_KEY_BYTES],
    uint8_t optional_out_seed[MLKEM_SEED_BYTES],
    struct MLKEM768_private_key *out_private_key);

/*
 * MLKEM768_private_key_from_seed derives a private key from a seed that was
 * generated by |MLKEM768_generate_key|. It fails and returns 0 if |seed_len| is
 * incorrect, otherwise it writes |*out_private_key| and returns 1.
 */
int MLKEM768_private_key_from_seed(struct MLKEM768_private_key *out_private_key,
    const uint8_t *seed, size_t seed_len);

/*
 * MLKEM_public_from_private sets |*out_public_key| to the public key that
 * corresponds to |private_key|. (This is faster than parsing the output of
 * |MLKEM_generate_key| if, for some reason, you need to encapsulate to a key
 * that was just generated.)
 */
void MLKEM768_public_from_private(struct MLKEM768_public_key *out_public_key,
    const struct MLKEM768_private_key *private_key);

/* MLKEM768_CIPHERTEXT_BYTES is number of bytes in the ML-KEM768 ciphertext. */
#define MLKEM768_CIPHERTEXT_BYTES 1088

/*
 * MLKEM768_encap encrypts a random shared secret for |public_key|, writes the
 * ciphertext to |out_ciphertext|, and writes the random shared secret to
 * |out_shared_secret|.
 */
void MLKEM768_encap(uint8_t out_ciphertext[MLKEM768_CIPHERTEXT_BYTES],
    uint8_t out_shared_secret[MLKEM_SHARED_SECRET_BYTES],
    const struct MLKEM768_public_key *public_key);

/*
 * MLKEM768_decap decrypts a shared secret from |ciphertext| using |private_key|
 * and writes it to |out_shared_secret|. If |ciphertext_len| is incorrect it
 * returns 0, otherwise it rreturns 1. If |ciphertext| is invalid,
 * |out_shared_secret| is filled with a key that will always be the same for the
 * same |ciphertext| and |private_key|, but which appears to be random unless
 * one has access to |private_key|. These alternatives occur in constant time.
 * Any subsequent symmetric encryption using |out_shared_secret| must use an
 * authenticated encryption scheme in order to discover the decapsulation
 * failure.
 */
int MLKEM768_decap(uint8_t out_shared_secret[MLKEM_SHARED_SECRET_BYTES],
    const uint8_t *ciphertext, size_t ciphertext_len,
    const struct MLKEM768_private_key *private_key);

/* Serialisation of keys. */

/*
 * MLKEM768_marshal_public_key serializes |public_key| to |out| in the standard
 * format for ML-KEM public keys. It returns one on success or zero on allocation
 * error.
 */
int MLKEM768_marshal_public_key(struct cbb_st *out,
    const struct MLKEM768_public_key *public_key);

/*
 * MLKEM768_parse_public_key parses a public key, in the format generated by
 * |MLKEM_marshal_public_key|, from |in| and writes the result to
 * |out_public_key|. It returns one on success or zero on parse error or if
 * there are trailing bytes in |in|.
 */
int MLKEM768_parse_public_key(struct MLKEM768_public_key *out_public_key,
    struct cbs_st *in);

/*
 * MLKEM_parse_private_key parses a private key, in the format generated by
 * |MLKEM_marshal_private_key|, from |in| and writes the result to
 * |out_private_key|. It returns one on success or zero on parse error or if
 * there are trailing bytes in |in|. This formate is verbose and should be avoided.
 * Private keys should be stored as seeds and parsed using |MLKEM768_private_key_from_seed|.
 */
int MLKEM768_parse_private_key(struct MLKEM768_private_key *out_private_key,
    struct cbs_st *in);

/*
 * ML-KEM-1024
 *
 * ML-KEM-1024 also exists. You should prefer ML-KEM-768 where possible.
 */

/*
 * MLKEM1024_public_key contains an ML-KEM-1024 public key. The contents of this
 * object should never leave the address space since the format is unstable.
 */
struct MLKEM1024_public_key {
	union {
		uint8_t bytes[512 * (4 + 16) + 32 + 32];
		uint16_t alignment;
	} opaque;
};

/*
 * MLKEM1024_private_key contains a ML-KEM-1024 private key. The contents of
 * this object should never leave the address space since the format is
 * unstable.
 */
struct MLKEM1024_private_key {
	union {
		uint8_t bytes[512 * (4 + 4 + 16) + 32 + 32 + 32];
		uint16_t alignment;
	} opaque;
};

/*
 * MLKEM1024_PUBLIC_KEY_BYTES is the number of bytes in an encoded ML-KEM-1024
 * public key.
 */
#define MLKEM1024_PUBLIC_KEY_BYTES 1568

/*
 * MLKEM1024_generate_key generates a random public/private key pair, writes the
 * encoded public key to |out_encoded_public_key| and sets |out_private_key| to
 * the private key. If |optional_out_seed| is not NULL then the seed used to
 * generate the private key is written to it.
 */
void MLKEM1024_generate_key(
    uint8_t out_encoded_public_key[MLKEM1024_PUBLIC_KEY_BYTES],
    uint8_t optional_out_seed[MLKEM_SEED_BYTES],
    struct MLKEM1024_private_key *out_private_key);

/*
 * MLKEM1024_private_key_from_seed derives a private key from a seed that was
 * generated by |MLKEM1024_generate_key|. It fails and returns 0 if |seed_len|
 * is incorrect, otherwise it writes |*out_private_key| and returns 1.
 */
int MLKEM1024_private_key_from_seed(
    struct MLKEM1024_private_key *out_private_key, const uint8_t *seed,
    size_t seed_len);

/*
 * MLKEM1024_public_from_private sets |*out_public_key| to the public key that
 * corresponds to |private_key|. (This is faster than parsing the output of
 * |MLKEM1024_generate_key| if, for some reason, you need to encapsulate to a
 * key that was just generated.)
 */
void MLKEM1024_public_from_private(struct MLKEM1024_public_key *out_public_key,
    const struct MLKEM1024_private_key *private_key);

/* MLKEM1024_CIPHERTEXT_BYTES is number of bytes in the ML-KEM-1024 ciphertext. */
#define MLKEM1024_CIPHERTEXT_BYTES 1568

/*
 * MLKEM1024_encap encrypts a random shared secret for |public_key|, writes the
 * ciphertext to |out_ciphertext|, and writes the random shared secret to
 * |out_shared_secret|.
 */
void MLKEM1024_encap(uint8_t out_ciphertext[MLKEM1024_CIPHERTEXT_BYTES],
    uint8_t out_shared_secret[MLKEM_SHARED_SECRET_BYTES],
    const struct MLKEM1024_public_key *public_key);

/*
 * MLKEM1024_decap decrypts a shared secret from |ciphertext| using
 * |private_key| and writes it to |out_shared_secret|. If |ciphertext_len| is
 * incorrect it returns 0, otherwise it returns 1. If |ciphertext| is invalid
 * (but of the correct length), |out_shared_secret| is filled with a key that
 * will always be the same for the same |ciphertext| and |private_key|, but
 * which appears to be random unless one has access to |private_key|. These
 * alternatives occur in constant time. Any subsequent symmetric encryption
 * using |out_shared_secret| must use an authenticated encryption scheme in
 * order to discover the decapsulation failure.
 */
int MLKEM1024_decap(uint8_t out_shared_secret[MLKEM_SHARED_SECRET_BYTES],
    const uint8_t *ciphertext, size_t ciphertext_len,
    const struct MLKEM1024_private_key *private_key);

/*
 * Serialisation of ML-KEM-1024 keys.
 * MLKEM1024_marshal_public_key serializes |public_key| to |out| in the standard
 * format for ML-KEM-1024 public keys. It returns one on success or zero on
 * allocation error.
 */
int MLKEM1024_marshal_public_key(struct cbb_st *out,
    const struct MLKEM1024_public_key *public_key);

/*
 * MLKEM1024_parse_public_key parses a public key, in the format generated by
 * |MLKEM1024_marshal_public_key|, from |in| and writes the result to
 * |out_public_key|. It returns one on success or zero on parse error or if
 * there are trailing bytes in |in|.
 */
int MLKEM1024_parse_public_key(struct MLKEM1024_public_key *out_public_key,
    struct cbs_st *in);

/*
 * MLKEM1024_parse_private_key parses a private key, in NIST's format for
 * private keys, from |in| and writes the result to |out_private_key|. It
 * returns one on success or zero on parse error or if there are trailing bytes
 * in |in|. This format is verbose and should be avoided. Private keys should be
 * stored as seeds and parsed using |MLKEM1024_private_key_from_seed|.
 */
int MLKEM1024_parse_private_key(struct MLKEM1024_private_key *out_private_key,
    struct cbs_st *in);

#if defined(__cplusplus)
}
#endif

#endif  /* OPENSSL_HEADER_MLKEM_H */