Method ProcessReceivedKeyBytes

src/net.cpp:1125–1183

}

bool V2Transport::ProcessReceivedKeyBytes() noexcept
{
    AssertLockHeld(m_recv_mutex);
    AssertLockNotHeld(m_send_mutex);
    Assume(m_recv_state == RecvState::KEY);
    Assume(m_recv_buffer.size() <= EllSwiftPubKey::size());

    // As a special exception, if bytes 4-16 of the key on a responder connection match the
    // corresponding bytes of a V1 version message, but bytes 0-4 don't match the network magic
    // (if they did, we'd have switched to V1 state already), assume this is a peer from
    // another network, and disconnect them. They will almost certainly disconnect us too when
    // they receive our uniformly random key and garbage, but detecting this case specially
    // means we can log it.
    static constexpr std::array<uint8_t, 12> MATCH = {'v', 'e', 'r', 's', 'i', 'o', 'n', 0, 0, 0, 0, 0};
    static constexpr size_t OFFSET = std::tuple_size_v<MessageStartChars>;
    if (!m_initiating && m_recv_buffer.size() >= OFFSET + MATCH.size()) {
        if (std::equal(MATCH.begin(), MATCH.end(), m_recv_buffer.begin() + OFFSET)) {
            LogDebug(BCLog::NET, "V2 transport error: V1 peer with wrong MessageStart %s\n",
                     HexStr(std::span(m_recv_buffer).first(OFFSET)));
            return false;
        }
    }

    if (m_recv_buffer.size() == EllSwiftPubKey::size()) {
        // Other side's key has been fully received, and can now be Diffie-Hellman combined with
        // our key to initialize the encryption ciphers.

        // Initialize the ciphers.
        EllSwiftPubKey ellswift(MakeByteSpan(m_recv_buffer));
        LOCK(m_send_mutex);
        m_cipher.Initialize(ellswift, m_initiating);

        // Switch receiver state to GARB_GARBTERM.
        SetReceiveState(RecvState::GARB_GARBTERM);
        m_recv_buffer.clear();

        // Switch sender state to READY.
        SetSendState(SendState::READY);

        // Append the garbage terminator to the send buffer.
        m_send_buffer.resize(m_send_buffer.size() + BIP324Cipher::GARBAGE_TERMINATOR_LEN);
        std::copy(m_cipher.GetSendGarbageTerminator().begin(),
                  m_cipher.GetSendGarbageTerminator().end(),
                  MakeWritableByteSpan(m_send_buffer).last(BIP324Cipher::GARBAGE_TERMINATOR_LEN).begin());

        // Construct version packet in the send buffer, with the sent garbage data as AAD.
        m_send_buffer.resize(m_send_buffer.size() + BIP324Cipher::EXPANSION + VERSION_CONTENTS.size());
        m_cipher.Encrypt(
            /*contents=*/VERSION_CONTENTS,
            /*aad=*/MakeByteSpan(m_send_garbage),
            /*ignore=*/false,
            /*output=*/MakeWritableByteSpan(m_send_buffer).last(BIP324Cipher::EXPANSION + VERSION_CONTENTS.size()));
        // We no longer need the garbage.
        ClearShrink(m_send_garbage);
    } else {
        // We still have to receive more key bytes.
    }
    return true;