nuttx/include/crypto/curve25519.h

/****************************************************************************
 * include/crypto/curve25519.h
 * $OpenBSD: curve25519.h,v 1.2 2020/07/22 13:54:30 tobhe Exp $
 *
 * Copyright (C) 2019-2020 Matt Dunwoodie <ncon@noconroy.net>
 *
 * Permission to use, copy, modify, and 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 __INCLUDE_CRYPTO_CURVE25519_H
#define __INCLUDE_CRYPTO_CURVE25519_H

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <stdlib.h>

#define CURVE25519_KEY_SIZE 32

int curve25519(uint8_t out[CURVE25519_KEY_SIZE],
               const uint8_t scalar[CURVE25519_KEY_SIZE],
               const uint8_t point[CURVE25519_KEY_SIZE]);

int curve25519_generate_public(uint8_t pub[CURVE25519_KEY_SIZE],
                         const uint8_t secret[CURVE25519_KEY_SIZE]);

static inline void
curve25519_clamp_secret(uint8_t secret[CURVE25519_KEY_SIZE])
{
    secret[0] &= 248;
    secret[31] = (secret[31] & 127) | 64;
}

static inline void
curve25519_generate_secret(uint8_t secret[CURVE25519_KEY_SIZE])
{
    arc4random_buf(secret, CURVE25519_KEY_SIZE);
    curve25519_clamp_secret(secret);
}
#endif /* __INCLUDE_CRYPTO_CURVE25519_H */