Function Strengthen

src/random.cpp:224–249

Use repeated SHA512 to strengthen the randomness in seed32, and feed into hasher. */

/** Use repeated SHA512 to strengthen the randomness in seed32, and feed into hasher. */
static void Strengthen(const unsigned char (&seed)[32], int microseconds, CSHA512& hasher) noexcept
{
    CSHA512 inner_hasher;
    inner_hasher.Write(seed, sizeof(seed));

    // Hash loop
    unsigned char buffer[64];
    int64_t stop = GetTimeMicros() + microseconds;
    do {
        for (int i = 0; i < 1000; ++i) {
            inner_hasher.Finalize(buffer);
            inner_hasher.Reset();
            inner_hasher.Write(buffer, sizeof(buffer));
        }
        // Benchmark operation and feed it into outer hasher.
        int64_t perf = GetPerformanceCounter();
        hasher.Write((const unsigned char*)&perf, sizeof(perf));
    } while (GetTimeMicros() < stop);

    // Produce output from inner state and feed it to outer hasher.
    inner_hasher.Finalize(buffer);
    hasher.Write(buffer, sizeof(buffer));
    // Try to clean up.
    inner_hasher.Reset();
    memory_cleanse(buffer, sizeof(buffer));
}

#ifndef WIN32
/** Fallback: get 32 bytes of system entropy from /dev/urandom. The most