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/*
* Copyright (c) 2017 embedded brains GmbH. All rights reserved.
*
* embedded brains GmbH
* Dornierstr. 4
* 82178 Puchheim
* Germany
* <rtems@embedded-brains.de>
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.org/license/LICENSE.
*/
/*
* ATTENTION: THIS IS A VERY LIMITED ENTROPY SOURCE.
*
* This implementation uses a time-based value for it's entropy. The only thing
* that makes it random are interrupts from external sources. Don't use it if
* you need for example a strong crypto.
*/
#include <sys/param.h>
#include <unistd.h>
#include <string.h>
#include <rtems/bsd.h>
#include <rtems/counter.h>
#include <rtems/sysinit.h>
static uint32_t state;
int getentropy(void *ptr, size_t n)
{
uint8_t *dest = ptr;
state ^= rtems_counter_read();
state *= 25169206;
state += 1679610226;
while (n > 0) {
size_t m;
m = MIN(n, sizeof(state));
memcpy(dest, &state, m);
n -= m;
dest += m;
state *= 85236167;
state += 30557471;
}
return 0;
}
static void getentropy_init(void)
{
struct bintime bt;
rtems_bsd_bintime(&bt);
state = (uint32_t) bt.frac;
state ^= (uint32_t) (bt.frac >> 32);
state ^= (uint32_t) bt.sec;
state ^= (uint32_t) (bt.sec >> 32);
}
RTEMS_SYSINIT_ITEM(
getentropy_init,
RTEMS_SYSINIT_DEVICE_DRIVERS,
RTEMS_SYSINIT_ORDER_LAST
);
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