kyber.h

All headers
  1. KYBER_public_key
  2. KYBER_private_key
  3. KYBER_PUBLIC_KEY_BYTES
  4. KYBER_SHARED_SECRET_BYTES
  5. KYBER_generate_key
  6. KYBER_public_from_private
  7. KYBER_CIPHERTEXT_BYTES
  8. KYBER_encap
  9. KYBER_decap
  10. Serialisation of keys
  11. KYBER_marshal_public_key
  12. KYBER_parse_public_key
  13. KYBER_marshal_private_key
  14. KYBER_PRIVATE_KEY_BYTES
  15. KYBER_parse_private_key
#if defined(OPENSSL_UNSTABLE_EXPERIMENTAL_KYBER)

This header implements experimental, draft versions of not-yet-standardized primitives. When the standard is complete, these functions will be removed and replaced with the final, incompatible standard version. They are available now for short-lived experiments, but must not be deployed anywhere durable, such as a long-lived key store. To use these functions define OPENSSL_UNSTABLE_EXPERIMENTAL_KYBER

Kyber768.

This implements the round-3 specification of Kyber, defined at https://pq-crystals.org/kyber/data/kyber-specification-round3-20210804.pdf

KYBER_public_key contains a Kyber768 public key. The contents of this object should never leave the address space since the format is unstable.

struct KYBER_public_key {
  union {
    uint8_t bytes[512 * (3 + 9) + 32 + 32];
    uint16_t alignment;
  } opaque;
};

KYBER_private_key contains a Kyber768 private key. The contents of this object should never leave the address space since the format is unstable.

struct KYBER_private_key {
  union {
    uint8_t bytes[512 * (3 + 3 + 9) + 32 + 32 + 32];
    uint16_t alignment;
  } opaque;
};

KYBER_PUBLIC_KEY_BYTES is the number of bytes in an encoded Kyber768 public key.

#define KYBER_PUBLIC_KEY_BYTES 1184

KYBER_SHARED_SECRET_BYTES is the number of bytes in the Kyber768 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 KYBER_SHARED_SECRET_BYTES 32

KYBER_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.

OPENSSL_EXPORT void KYBER_generate_key(
    uint8_t out_encoded_public_key[KYBER_PUBLIC_KEY_BYTES],
    struct KYBER_private_key *out_private_key);

KYBER_public_from_private sets *out_public_key to the public key that corresponds to private_key. (This is faster than parsing the output of KYBER_generate_key if, for some reason, you need to encapsulate to a key that was just generated.)

OPENSSL_EXPORT void KYBER_public_from_private(
    struct KYBER_public_key *out_public_key,
    const struct KYBER_private_key *private_key);

KYBER_CIPHERTEXT_BYTES is number of bytes in the Kyber768 ciphertext.

#define KYBER_CIPHERTEXT_BYTES 1088

KYBER_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.

OPENSSL_EXPORT void KYBER_encap(
    uint8_t out_ciphertext[KYBER_CIPHERTEXT_BYTES],
    uint8_t out_shared_secret[KYBER_SHARED_SECRET_BYTES],
    const struct KYBER_public_key *public_key);

KYBER_decap decrypts a shared secret from ciphertext using private_key and writes it to out_shared_secret. 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.

OPENSSL_EXPORT void KYBER_decap(
    uint8_t out_shared_secret[KYBER_SHARED_SECRET_BYTES],
    const uint8_t ciphertext[KYBER_CIPHERTEXT_BYTES],
    const struct KYBER_private_key *private_key);

Serialisation of keys.

KYBER_marshal_public_key serializes public_key to out in the standard format for Kyber public keys. It returns one on success or zero on allocation error.

OPENSSL_EXPORT int KYBER_marshal_public_key(
    CBB *out, const struct KYBER_public_key *public_key);

KYBER_parse_public_key parses a public key, in the format generated by KYBER_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.

OPENSSL_EXPORT int KYBER_parse_public_key(
    struct KYBER_public_key *out_public_key, CBS *in);

KYBER_marshal_private_key serializes private_key to out in the standard format for Kyber private keys. It returns one on success or zero on allocation error.

OPENSSL_EXPORT int KYBER_marshal_private_key(
    CBB *out, const struct KYBER_private_key *private_key);

KYBER_PRIVATE_KEY_BYTES is the length of the data produced by KYBER_marshal_private_key.

#define KYBER_PRIVATE_KEY_BYTES 2400

KYBER_parse_private_key parses a private key, in the format generated by KYBER_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.

OPENSSL_EXPORT int KYBER_parse_private_key(
    struct KYBER_private_key *out_private_key, CBS *in);
#endif // OPENSSL_UNSTABLE_EXPERIMENTAL_KYBER