src/core/common/random_manager.cpp

/*
 *  Copyright (c) 2019, The OpenThread Authors.
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 *     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.
 *  3. Neither the name of the copyright holder nor the
 *     names of its contributors may be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 */

/**
 * @file
 *   This file provides an implementation of OpenThread random number generation manager class.
 */

#include "random_manager.hpp"

#include <openthread/platform/entropy.h>

#include "common/code_utils.hpp"
#include "common/debug.hpp"
#include "common/logging.hpp"
#include "common/random.hpp"
#include "crypto/mbedtls.hpp"

namespace ot {

uint16_t                     RandomManager::sInitCount = 0;
RandomManager::NonCryptoPrng RandomManager::sPrng;

RandomManager::RandomManager(void)
{
    uint32_t seed;

    OT_ASSERT(sInitCount < 0xffff);

    VerifyOrExit(sInitCount == 0);

#if !OPENTHREAD_RADIO
    otPlatCryptoRandomInit();
    SuccessOrAssert(Random::Crypto::FillBuffer(reinterpret_cast<uint8_t *>(&seed), sizeof(seed)));
#else
    SuccessOrAssert(otPlatEntropyGet(reinterpret_cast<uint8_t *>(&seed), sizeof(seed)));
#endif

    sPrng.Init(seed);

exit:
    sInitCount++;
}

RandomManager::~RandomManager(void)
{
    OT_ASSERT(sInitCount > 0);

    sInitCount--;
    VerifyOrExit(sInitCount == 0);

#if !OPENTHREAD_RADIO
    otPlatCryptoRandomDeinit();
#endif

exit:
    return;
}

uint32_t RandomManager::NonCryptoGetUint32(void)
{
    OT_ASSERT(sInitCount > 0);

    return sPrng.GetNext();
}

//-------------------------------------------------------------------
// NonCryptoPrng

void RandomManager::NonCryptoPrng::Init(uint32_t aSeed)
{
    // The PRNG has a cycle of length 1 for the below two initial
    // seeds. For all other seed values the cycle is ~2^31 long.

    if ((aSeed == 0) || (aSeed == 0x7fffffff))
    {
        aSeed = 0x1;
    }

    mState = aSeed;
}

uint32_t RandomManager::NonCryptoPrng::GetNext(void)
{
    uint32_t mlcg, p, q;
    uint64_t tmpstate;

    tmpstate = static_cast<uint64_t>(33614) * static_cast<uint64_t>(mState);
    q        = tmpstate & 0xffffffff;
    q        = q >> 1;
    p        = tmpstate >> 32;
    mlcg     = p + q;

    if (mlcg & 0x80000000)
    {
        mlcg &= 0x7fffffff;
        mlcg++;
    }

    mState = mlcg;

    return mlcg;
}

} // namespace ot