tetatet/src/crypt.h

#ifndef _CRYPT_H_
#define _CRYPT_H_

#include <stdio.h>
#include <stdbool.h>

#include <sodium.h>

#define CRYPT_KX_PKEY_LEN crypto_kx_PUBLICKEYBYTES
#define CRYPT_KX_SKEY_LEN crypto_kx_SECRETKEYBYTES

#define CRYPT_SIGN_PKEY_LEN crypto_sign_PUBLICKEYBYTES
#define CRYPT_SIGN_SKEY_LEN crypto_sign_SECRETKEYBYTES
#define CRYPT_SIGN_LEN crypto_sign_BYTES

#define CRYPT_SESS_KEY_LEN crypto_kx_SESSIONKEYBYTES

#define CRYPT_NONCE_LEN crypto_aead_aegis256_NPUBBYTES
#define CRYPT_NONCEHALF_LEN (CRYPT_NONCE_LEN/2)

#define CRYPT_HELLO_LEN (CRYPT_PKEY_HEXLEN + CRYPT_SIGN_LEN + (CRYPT_NONCEHALF_LEN))

#define CRYPT_PKEY_HEXLEN ((CRYPT_KX_PKEY_LEN + CRYPT_SIGN_PKEY_LEN) * 2)
#define CRYPT_SKEY_HEXLEN ((CRYPT_SIGN_PKEY_LEN + CRYPT_SIGN_SKEY_LEN) * 2)

// Stores the public and secret keys used in a key exchange and for signing.
typedef struct crypt_key_t {
    unsigned char kx_pub[crypto_kx_PUBLICKEYBYTES];
    unsigned char kx_sec[crypto_kx_SECRETKEYBYTES];
    unsigned char sign_pub[crypto_sign_PUBLICKEYBYTES];
    unsigned char sign_sec[crypto_sign_SECRETKEYBYTES];
    bool hasSecKey;
} crypt_key_t;

// Generates the new pairs of a key exchange and sign keys.
int crypt_key_gen(crypt_key_t *const k);
// Initialise a crypt_key_t with a provided hex representaions of public and secret keys.
int crypt_key_from_hex(crypt_key_t *const k, const char phex[CRYPT_PKEY_HEXLEN], const char shex[CRYPT_SKEY_HEXLEN]);
// Initialise a crypt_key_t with a provided hex representaion of just a public key. Used for remote keys.
int crypt_key_from_hex_public(crypt_key_t *const k, const char phex[CRYPT_PKEY_HEXLEN]);

// Securely erase the fields of a crypt_key_t struct.
void crypt_key_destroy(crypt_key_t *const k);

// Export a public sign and key exchange keys as a hex string.
int crypt_key_export_public(const crypt_key_t *const k, char hex[CRYPT_PKEY_HEXLEN]);
// Export a secret sign and key exchange keys as a hex string.
int crypt_key_export_secret(const crypt_key_t *const k, char hex[CRYPT_SKEY_HEXLEN]);

// Load the sign and key exchange keys in a hex representaion from files
// and initialise a crypt_key_t.
int crypt_load_key(crypt_key_t *const k, FILE *const pub, FILE *const sec);
// Store a hex representaion of the sign and key exchange keys into files
// that are corresponding to a public and a secret parts.
int crypt_store_key(const crypt_key_t *const k, FILE *const pub, FILE *const sec);

// Returns a hello packet consisting of a public key and its sign.
// The packet is of CRYPT_SIGN_LEN long.
unsigned char *crypt_hello(const crypt_key_t *const own);
// Verify a hello message. It only shows that a remote public key's sign is ok.
int crypt_hello_verify(const unsigned char *const hello, crypt_key_t *const remote);
// Combines own and remote halves of a nonce depending in a connection direction and returns it.
// It will be of CRYPT_NONCE_LEN length.
const unsigned char *crypt_hello_get_nonce(const unsigned char *const own_hello, const unsigned char *const remote_hello, const bool is_client);

// Stores symmetric keys used for a data encryption in both directions
// and a remote public key.
typedef struct crypt_session_t {
    unsigned char rx[CRYPT_SESS_KEY_LEN];
    unsigned char tx[CRYPT_SESS_KEY_LEN];
    crypt_key_t *remote_key;
} crypt_session_t;

// Derives the symmetric keys for a data encryption using own public and secret and remote's public keys.
//
// is_client should be set to true if you are the one establishing the connection.
int crypt_session_init(crypt_session_t *const s, const crypt_key_t *const own, crypt_key_t *const remote, const bool is_client);
// Securely erase the fields of a crypt_session_t struct.
void crypt_session_destroy(crypt_session_t *const s);

#endif /* _CRYPT_H_ */