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83 lines
2.4 KiB
C
83 lines
2.4 KiB
C
/* SPDX-License-Identifier: BSD-2-Clause */
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/*
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* Copyright (c) 2017 embedded brains GmbH & Co. KG
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* ATTENTION: THIS IS A VERY LIMITED ENTROPY SOURCE.
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*
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* This implementation uses a time-based value for it's entropy. The only thing
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* that makes it random are interrupts from external sources. Don't use it if
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* you need for example a strong crypto.
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*/
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#include <sys/param.h>
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#include <unistd.h>
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#include <string.h>
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#include <rtems/bsd.h>
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#include <rtems/counter.h>
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#include <rtems/sysinit.h>
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static uint32_t state;
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int getentropy(void *ptr, size_t n)
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{
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uint8_t *dest = ptr;
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state ^= rtems_counter_read();
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state *= 25169206;
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state += 1679610226;
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while (n > 0) {
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size_t m;
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m = MIN(n, sizeof(state));
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memcpy(dest, &state, m);
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n -= m;
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dest += m;
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state *= 85236167;
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state += 30557471;
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}
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return 0;
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}
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static void getentropy_init(void)
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{
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struct bintime bt;
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rtems_bsd_bintime(&bt);
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state = (uint32_t) bt.frac;
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state ^= (uint32_t) (bt.frac >> 32);
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state ^= (uint32_t) bt.sec;
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state ^= (uint32_t) (bt.sec >> 32);
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}
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RTEMS_SYSINIT_ITEM(
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getentropy_init,
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RTEMS_SYSINIT_DEVICE_DRIVERS,
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RTEMS_SYSINIT_ORDER_LAST_BUT_5
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);
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