lora-irrigation/strobe_rng_init.c

/*-
 * Copyright 2021 John-Mark Gurney.
 *
 * 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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.
 *
 */

#include <strobe.h>

#include <strobe_rng_init.h>

/*
 * Note: rng_save is really REAL_RNG_SAVE_LEN, BUT, we want to use the
 * uninitalized SRAM after it as entropy.
 */
extern uint8_t rng_save[2*1048];
extern int rng_save_len;

#define REAL_RNG_SAVE_LEN       ((int)&rng_save_len)

void
strobe_rng_init(void)
{
	int r;

	/*
	 * Seed RNG
	 * On first boot, SRAM is uninitialized and randomness from
	 * it is used.  On reset, the previously saved state is used.
	 */
	strobe_seed_prng(rng_save, 2*1024);

	/*
	 * Save entropy for next reset.
	 */
	r = strobe_randomize(rng_save, REAL_RNG_SAVE_LEN);
	(void)r;
}