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trezor-firmware/embed/trezorhal/rng.c
2018-02-26 14:07:37 +01:00

57 lines
1.9 KiB
C

/*
* This file is part of the TREZOR project, https://trezor.io/
*
* Copyright (c) SatoshiLabs
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include STM32_HAL_H
#include "rng.h"
#pragma GCC optimize("no-stack-protector") // applies to all functions in this file
void rng_init(void)
{
// enable TRNG peripheral clock
// use the HAL version due to section 2.1.6 of STM32F42xx Errata sheet
// "Delay after an RCC peripheral clock enabling"
__HAL_RCC_RNG_CLK_ENABLE();
RNG->CR = RNG_CR_RNGEN; // enable TRNG
}
uint32_t rng_read(const uint32_t previous, const uint32_t compare_previous)
{
uint32_t temp = previous;
do {
while ((RNG->SR & (RNG_SR_SECS | RNG_SR_CECS | RNG_SR_DRDY)) != RNG_SR_DRDY); // wait until TRNG is ready
temp = RNG->DR; // read the data from the TRNG
} while (compare_previous && (temp == previous)); // RM0090 section 24.3.1 FIPS continuous random number generator test
return temp;
}
uint32_t rng_get(void)
{
// reason for keeping history: RM0090 section 24.3.1 FIPS continuous random number generator test
static uint32_t previous = 0, current = 0;
if (previous == current) {
previous = rng_read(previous, 0);
} else {
previous = current;
}
current = rng_read(previous, 1);
return current;
}