Class RNGState

src/random.cpp:340–448

}

class RNGState {
    Mutex m_mutex;
    /* The RNG state consists of 256 bits of entropy, taken from the output of
     * one operation's SHA512 output, and fed as input to the next one.
     * Carrying 256 bits of entropy should be sufficient to guarantee
     * unpredictability as long as any entropy source was ever unpredictable
     * to an attacker. To protect against situations where an attacker might
     * observe the RNG's state, fresh entropy is always mixed when
     * GetStrongRandBytes is called.
     */
    unsigned char m_state[32] GUARDED_BY(m_mutex) = {0};
    uint64_t m_counter GUARDED_BY(m_mutex) = 0;
    bool m_strongly_seeded GUARDED_BY(m_mutex) = false;

    /** If not nullopt, the output of this RNGState is redirected and drawn from here
     *  (unless always_use_real_rng is passed to MixExtract). */
    std::optional<ChaCha20> m_deterministic_prng GUARDED_BY(m_mutex);

    Mutex m_events_mutex;
    CSHA256 m_events_hasher GUARDED_BY(m_events_mutex);

public:
    RNGState() noexcept
    {
        InitHardwareRand();
    }

    ~RNGState() = default;

    void AddEvent(uint32_t event_info) noexcept EXCLUSIVE_LOCKS_REQUIRED(!m_events_mutex)
    {
        LOCK(m_events_mutex);

        m_events_hasher.Write((const unsigned char *)&event_info, sizeof(event_info));
        // Get the low four bytes of the performance counter. This translates to roughly the
        // subsecond part.
        uint32_t perfcounter = (GetPerformanceCounter() & 0xffffffff);
        m_events_hasher.Write((const unsigned char*)&perfcounter, sizeof(perfcounter));
    }

    /**
     * Feed (the hash of) all events added through AddEvent() to hasher.
     */
    void SeedEvents(CSHA512& hasher) noexcept EXCLUSIVE_LOCKS_REQUIRED(!m_events_mutex)
    {
        // We use only SHA256 for the events hashing to get the ASM speedups we have for SHA256,
        // since we want it to be fast as network peers may be able to trigger it repeatedly.
        LOCK(m_events_mutex);

        unsigned char events_hash[32];
        m_events_hasher.Finalize(events_hash);
        hasher.Write(events_hash, 32);

        // Re-initialize the hasher with the finalized state to use later.
        m_events_hasher.Reset();
        m_events_hasher.Write(events_hash, 32);
    }