rc-random.c

/*
 * Copyright (C) 2026 Nikos Mavrogiannopoulos
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
 
/* This is the single place that dispatches to gnutls_rnd()/getentropy();
 * every Request Authenticator and packet-ID generator in the library goes
 * through it instead of duplicating the #if defined(HAVE_GNUTLS) branch.
 * See REQ-GEN-SEC-007 in doc/requirements/general.md. */
 
#include <config.h>
#include "rc-random.h"
 
#include <assert.h>
 
#if defined(HAVE_GNUTLS)
# include <gnutls/gnutls.h>
# include <gnutls/crypto.h>
#endif
 
/*- Fill a buffer with cryptographically random bytes, via gnutls_rnd() or
 * getentropy().
 *
 * @param buf the buffer to fill.
 * @param len the number of random bytes to write into buf.
 -*/
void rc_get_random_bytes(void *buf, size_t len)
{
#if defined(HAVE_GNUTLS)
        int ret = gnutls_rnd(GNUTLS_RND_NONCE, buf, len);
        assert(ret >= 0);
#else
        int ret = getentropy(buf, len);
        assert(ret == 0);
#endif
}
 
/*- Return a single cryptographically random byte.
 -*/
unsigned char rc_get_random_byte(void)
{
        unsigned char b;
        rc_get_random_bytes(&b, 1);
        return b;
}