Merge pull request #5793

bdfc63a Add ref-counted buffer byte_slice. Currently used for sending TCP data. (vtnerd)
3b24b1d Added support for 'noise' over I1P/Tor to mask Tx transmission. (vtnerd)

3 files changed, 709 insertions, 61 deletions

diff --git a/src/cryptonote_protocol/cryptonote_protocol_handler.inl b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
index 2ff7b5938..7bd4eeead 100644
--- a/src/cryptonote_protocol/cryptonote_protocol_handler.inl
+++ b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
@@ -2227,69 +2227,11 @@ skip:
   template<class t_core>
   bool t_cryptonote_protocol_handler<t_core>::relay_transactions(NOTIFY_NEW_TRANSACTIONS::request& arg, cryptonote_connection_context& exclude_context)
   {
-    const bool hide_tx_broadcast =
-      1 < m_p2p->get_zone_count() && exclude_context.m_remote_address.get_zone() == epee::net_utils::zone::invalid;
-
-    if (hide_tx_broadcast)
-      MDEBUG("Attempting to conceal origin of tx via anonymity network connection(s)");
+    for(auto& tx_blob : arg.txs)
+      m_core.on_transaction_relayed(tx_blob);
 
     // no check for success, so tell core they're relayed unconditionally
-    const bool pad_transactions = m_core.pad_transactions() || hide_tx_broadcast;
-    size_t bytes = pad_transactions ? 9 /* header */ + 4 /* 1 + 'txs' */ + tools::get_varint_data(arg.txs.size()).size() : 0;
-    for(auto tx_blob_it = arg.txs.begin(); tx_blob_it!=arg.txs.end(); ++tx_blob_it)
-    {
-      m_core.on_transaction_relayed(*tx_blob_it);
-      if (pad_transactions)
-        bytes += tools::get_varint_data(tx_blob_it->size()).size() + tx_blob_it->size();
-    }
-
-    if (pad_transactions)
-    {
-      // stuff some dummy bytes in to stay safe from traffic volume analysis
-      static constexpr size_t granularity = 1024;
-      size_t padding = granularity - bytes % granularity;
-      const size_t overhead = 2 /* 1 + '_' */ + tools::get_varint_data(padding).size();
-      if (overhead > padding)
-        padding = 0;
-      else
-        padding -= overhead;
-      arg._ = std::string(padding, ' ');
-
-      std::string arg_buff;
-      epee::serialization::store_t_to_binary(arg, arg_buff);
-
-      // we probably lowballed the payload size a bit, so added a but too much. Fix this now.
-      size_t remove = arg_buff.size() % granularity;
-      if (remove > arg._.size())
-        arg._.clear();
-      else
-        arg._.resize(arg._.size() - remove);
-      // if the size of _ moved enough, we might lose byte in size encoding, we don't care
-    }
-
-    std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections;
-    m_p2p->for_each_connection([hide_tx_broadcast, &exclude_context, &connections](connection_context& context, nodetool::peerid_type peer_id, uint32_t support_flags)
-    {
-      const epee::net_utils::zone current_zone = context.m_remote_address.get_zone();
-      const bool broadcast_to_peer =
-        peer_id &&
-        (hide_tx_broadcast != bool(current_zone == epee::net_utils::zone::public_)) &&
-	exclude_context.m_connection_id != context.m_connection_id;
-
-      if (broadcast_to_peer)
-        connections.push_back({current_zone, context.m_connection_id});
-
-      return true;
-    });
-
-    if (connections.empty())
-      MERROR("Transaction not relayed - no" << (hide_tx_broadcast ? " privacy": "") << " peers available");
-    else
-    {
-      std::string fullBlob;
-      epee::serialization::store_t_to_binary(arg, fullBlob);
-      m_p2p->relay_notify_to_list(NOTIFY_NEW_TRANSACTIONS::ID, epee::strspan<uint8_t>(fullBlob), std::move(connections));
-    }
+    m_p2p->send_txs(std::move(arg.txs), exclude_context.m_remote_address.get_zone(), exclude_context.m_connection_id, m_core.pad_transactions());
     return true;
   }
   //------------------------------------------------------------------------------------------------------------------------
diff --git a/src/cryptonote_protocol/levin_notify.cpp b/src/cryptonote_protocol/levin_notify.cpp
new file mode 100644
index 000000000..26cd93b5a
--- /dev/null
+++ b/src/cryptonote_protocol/levin_notify.cpp
@@ -0,0 +1,574 @@
+// Copyright (c) 2019, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright 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 IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "levin_notify.h"
+
+#include <boost/asio/steady_timer.hpp>
+#include <boost/system/system_error.hpp>
+#include <chrono>
+#include <deque>
+#include <stdexcept>
+
+#include "common/expect.h"
+#include "common/varint.h"
+#include "cryptonote_config.h"
+#include "crypto/random.h"
+#include "cryptonote_basic/connection_context.h"
+#include "cryptonote_protocol/cryptonote_protocol_defs.h"
+#include "net/dandelionpp.h"
+#include "p2p/net_node.h"
+
+namespace cryptonote
+{
+namespace levin
+{
+  namespace
+  {
+    constexpr std::size_t connection_id_reserve_size = 100;
+
+    constexpr const std::chrono::minutes noise_min_epoch{CRYPTONOTE_NOISE_MIN_EPOCH};
+    constexpr const std::chrono::seconds noise_epoch_range{CRYPTONOTE_NOISE_EPOCH_RANGE};
+
+    constexpr const std::chrono::seconds noise_min_delay{CRYPTONOTE_NOISE_MIN_DELAY};
+    constexpr const std::chrono::seconds noise_delay_range{CRYPTONOTE_NOISE_DELAY_RANGE};
+
+    /*! Select a randomized duration from 0 to `range`. The precision will be to
+        the systems `steady_clock`. As an example, supplying 3 seconds to this
+        function will select a duration from [0, 3] seconds, and the increments
+        for the selection will be determined by the `steady_clock` precision
+        (typically nanoseconds).
+
+        \return A randomized duration from 0 to `range`. */
+    std::chrono::steady_clock::duration random_duration(std::chrono::steady_clock::duration range)
+    {
+      using rep = std::chrono::steady_clock::rep;
+      return std::chrono::steady_clock::duration{crypto::rand_range(rep(0), range.count())};
+    }
+
+    //! \return All outgoing connections supporting fragments in `connections`.
+    std::vector<boost::uuids::uuid> get_out_connections(connections& p2p)
+    {
+      std::vector<boost::uuids::uuid> outs;
+      outs.reserve(connection_id_reserve_size);
+
+      /* The foreach call is serialized with a lock, but should be quick due to
+         the reserve call so a strand is not used. Investigate if there is lots
+         of waiting in here. */
+
+      p2p.foreach_connection([&outs] (detail::p2p_context& context) {
+        if (!context.m_is_income)
+          outs.emplace_back(context.m_connection_id);
+        return true;
+      });
+
+      return outs;
+    }
+
+    std::string make_tx_payload(std::vector<blobdata>&& txs, const bool pad)
+    {
+      NOTIFY_NEW_TRANSACTIONS::request request{};
+      request.txs = std::move(txs);
+
+      if (pad)
+      {
+        size_t bytes = 9 /* header */ + 4 /* 1 + 'txs' */ + tools::get_varint_data(request.txs.size()).size();
+        for(auto tx_blob_it = request.txs.begin(); tx_blob_it!=request.txs.end(); ++tx_blob_it)
+          bytes += tools::get_varint_data(tx_blob_it->size()).size() + tx_blob_it->size();
+
+        // stuff some dummy bytes in to stay safe from traffic volume analysis
+        static constexpr const size_t granularity = 1024;
+        size_t padding = granularity - bytes % granularity;
+        const size_t overhead = 2 /* 1 + '_' */ + tools::get_varint_data(padding).size();
+        if (overhead > padding)
+          padding = 0;
+        else
+          padding -= overhead;
+        request._ = std::string(padding, ' ');
+
+        std::string arg_buff;
+        epee::serialization::store_t_to_binary(request, arg_buff);
+
+        // we probably lowballed the payload size a bit, so added a but too much. Fix this now.
+        size_t remove = arg_buff.size() % granularity;
+        if (remove > request._.size())
+          request._.clear();
+        else
+          request._.resize(request._.size() - remove);
+        // if the size of _ moved enough, we might lose byte in size encoding, we don't care
+      }
+
+      std::string fullBlob;
+      if (!epee::serialization::store_t_to_binary(request, fullBlob))
+        throw std::runtime_error{"Failed to serialize to epee binary format"};
+
+      return fullBlob;
+    }
+
+    /* The current design uses `asio::strand`s. The documentation isn't as clear
+       as it should be - a `strand` has an internal `mutex` and `bool`. The
+       `mutex` synchronizes thread access and the `bool` is set when a thread is
+       executing something "in the strand". Therefore, if a callback has lots of
+       work to do in a `strand`, asio can switch to some other task instead of
+       blocking 1+ threads to wait for the original thread to complete the task
+       (as is the case when client code has a `mutex` inside the callback). The
+       downside is that asio _always_ allocates for the callback, even if it can
+       be immediately executed. So if all work in a strand is minimal, a lock
+       may be better.
+
+       This code uses a strand per "zone" and a strand per "channel in a zone".
+       `dispatch` is used heavily, which means "execute immediately in _this_
+       thread if the strand is not in use, otherwise queue the callback to be
+       executed immediately after the strand completes its current task".
+       `post` is used where deferred execution to an `asio::io_service::run`
+       thread is preferred.
+
+       The strand per "zone" is useful because the levin
+       `foreach_connection` is blocked with a mutex anyway. So this primarily
+       helps with reducing blocking of a thread attempting a "flood"
+       notification. Updating/merging the outgoing connections in the
+       Dandelion++ map is also somewhat expensive.
+
+       The strand per "channel" may need a re-visit. The most "expensive" code
+       is figuring out the noise/notification to send. If levin code is
+       optimized further, it might be better to just use standard locks per
+       channel. */
+
+    //! A queue of levin messages for a noise i2p/tor link
+    struct noise_channel
+    {
+      explicit noise_channel(boost::asio::io_service& io_service)
+        : active(nullptr),
+          queue(),
+          strand(io_service),
+          next_noise(io_service),
+          connection(boost::uuids::nil_uuid())
+      {}
+
+      // `asio::io_service::strand` cannot be copied or moved
+      noise_channel(const noise_channel&) = delete;
+      noise_channel& operator=(const noise_channel&) = delete;
+
+      // Only read/write these values "inside the strand"
+
+      epee::byte_slice active;
+      std::deque<epee::byte_slice> queue;
+      boost::asio::io_service::strand strand;
+      boost::asio::steady_timer next_noise;
+      boost::uuids::uuid connection;
+    };
+  } // anonymous
+
+  namespace detail
+  {
+    struct zone
+    {
+      explicit zone(boost::asio::io_service& io_service, std::shared_ptr<connections> p2p, epee::byte_slice noise_in)
+        : p2p(std::move(p2p)),
+          noise(std::move(noise_in)),
+          next_epoch(io_service),
+          strand(io_service),
+          map(),
+          channels(),
+          connection_count(0)
+      {
+        for (std::size_t count = 0; !noise.empty() && count < CRYPTONOTE_NOISE_CHANNELS; ++count)
+          channels.emplace_back(io_service);
+      }
+
+      const std::shared_ptr<connections> p2p;
+      const epee::byte_slice noise; //!< `!empty()` means zone is using noise channels
+      boost::asio::steady_timer next_epoch;
+      boost::asio::io_service::strand strand;
+      net::dandelionpp::connection_map map;//!< Tracks outgoing uuid's for noise channels or Dandelion++ stems
+      std::deque<noise_channel> channels;  //!< Never touch after init; only update elements on `noise_channel.strand`
+      std::atomic<std::size_t> connection_count; //!< Only update in strand, can be read at any time
+    };
+  } // detail
+
+  namespace
+  {
+    //! Adds a message to the sending queue of the channel.
+    class queue_covert_notify
+    {
+      std::shared_ptr<detail::zone> zone_;
+      epee::byte_slice message_; // Requires manual copy constructor
+      const std::size_t destination_;
+
+    public:
+      queue_covert_notify(std::shared_ptr<detail::zone> zone, epee::byte_slice message, std::size_t destination)
+        : zone_(std::move(zone)), message_(std::move(message)), destination_(destination)
+      {}
+
+      queue_covert_notify(queue_covert_notify&&) = default;
+      queue_covert_notify(const queue_covert_notify& source)
+        : zone_(source.zone_), message_(source.message_.clone()), destination_(source.destination_)
+      {}
+
+      //! \pre Called within `zone_->channels[destionation_].strand`.
+      void operator()()
+      {
+        if (!zone_)
+          return;
+
+        noise_channel& channel = zone_->channels.at(destination_);
+        assert(channel.strand.running_in_this_thread());
+
+        if (!channel.connection.is_nil())
+          channel.queue.push_back(std::move(message_));
+      }
+    };
+
+    //! Sends a message to every active connection
+    class flood_notify
+    {
+      std::shared_ptr<detail::zone> zone_;
+      epee::byte_slice message_; // Requires manual copy
+      boost::uuids::uuid source_;
+
+    public:
+      explicit flood_notify(std::shared_ptr<detail::zone> zone, epee::byte_slice message, const boost::uuids::uuid& source)
+        : zone_(std::move(zone)), message_(message.clone()), source_(source)
+      {}
+
+      flood_notify(flood_notify&&) = default;
+      flood_notify(const flood_notify& source)
+        : zone_(source.zone_), message_(source.message_.clone()), source_(source.source_)
+      {}
+
+      void operator()() const
+      {
+        if (!zone_ || !zone_->p2p)
+          return;
+
+        assert(zone_->strand.running_in_this_thread());
+
+        /* The foreach should be quick, but then it iterates and acquires the
+           same lock for every connection. So do in a strand because two threads
+           will ping-pong each other with cacheline invalidations. Revisit if
+           algorithm changes or the locking strategy within the levin config
+           class changes. */
+
+        std::vector<boost::uuids::uuid> connections;
+        connections.reserve(connection_id_reserve_size);
+        zone_->p2p->foreach_connection([this, &connections] (detail::p2p_context& context) {
+          if (this->source_ != context.m_connection_id)
+            connections.emplace_back(context.m_connection_id);
+          return true;
+        });
+
+        for (const boost::uuids::uuid& connection : connections)
+          zone_->p2p->send(message_.clone(), connection);
+      }
+    };
+
+    //! Updates the connection for a channel.
+    struct update_channel
+    {
+      std::shared_ptr<detail::zone> zone_;
+      const std::size_t channel_;
+      const boost::uuids::uuid connection_;
+
+      //! \pre Called within `stem_.strand`.
+      void operator()() const
+      {
+        if (!zone_)
+          return;
+
+        noise_channel& channel = zone_->channels.at(channel_);
+        assert(channel.strand.running_in_this_thread());
+        static_assert(
+          CRYPTONOTE_MAX_FRAGMENTS <= (noise_min_epoch / (noise_min_delay + noise_delay_range)),
+          "Max fragments more than the max that can be sent in an epoch"
+        );
+
+        /* This clears the active message so that a message "in-flight" is
+           restarted. DO NOT try to send the remainder of the fragments, this
+           additional send time can leak that this node was sending out a real
+           notify (tx) instead of dummy noise. */
+
+        channel.connection = connection_;
+        channel.active = nullptr;
+
+        if (connection_.is_nil())
+          channel.queue.clear();
+      }
+    };
+
+    //! Merges `out_connections_` into the existing `zone_->map`.
+    struct update_channels
+    {
+      std::shared_ptr<detail::zone> zone_;
+      std::vector<boost::uuids::uuid> out_connections_;
+
+      //! \pre Called within `zone->strand`.
+      static void post(std::shared_ptr<detail::zone> zone)
+      {
+        if (!zone)
+          return;
+
+        assert(zone->strand.running_in_this_thread());
+
+        zone->connection_count = zone->map.size();
+        for (auto id = zone->map.begin(); id != zone->map.end(); ++id)
+        {
+          const std::size_t i = id - zone->map.begin();
+          zone->channels[i].strand.post(update_channel{zone, i, *id});
+        }
+      }
+
+      //! \pre Called within `zone_->strand`.
+      void operator()()
+      {
+        if (!zone_)
+          return;
+
+        assert(zone_->strand.running_in_this_thread());
+        if (zone_->map.update(std::move(out_connections_)))
+          post(std::move(zone_));
+      }
+    };
+
+    //! Swaps out noise channels entirely; new epoch start.
+    class change_channels
+    {
+      std::shared_ptr<detail::zone> zone_;
+      net::dandelionpp::connection_map map_; // Requires manual copy constructor
+
+    public:
+      explicit change_channels(std::shared_ptr<detail::zone> zone, net::dandelionpp::connection_map map)
+        : zone_(std::move(zone)), map_(std::move(map))
+      {}
+
+      change_channels(change_channels&&) = default;
+      change_channels(const change_channels& source)
+        : zone_(source.zone_), map_(source.map_.clone())
+      {}
+
+      //! \pre Called within `zone_->strand`.
+      void operator()()
+      {
+        if (!zone_)
+          return
+
+        assert(zone_->strand.running_in_this_thread());
+
+        zone_->map = std::move(map_);
+        update_channels::post(std::move(zone_));
+      }
+    };
+
+    //! Sends a noise packet or real notification and sets timer for next call.
+    struct send_noise
+    {
+      std::shared_ptr<detail::zone> zone_;
+      const std::size_t channel_;
+
+      static void wait(const std::chrono::steady_clock::time_point start, std::shared_ptr<detail::zone> zone, const std::size_t index)
+      {
+        if (!zone)
+          return;
+
+        noise_channel& channel = zone->channels.at(index);
+        channel.next_noise.expires_at(start + noise_min_delay + random_duration(noise_delay_range));
+        channel.next_noise.async_wait(
+          channel.strand.wrap(send_noise{std::move(zone), index})
+        );
+      }
+
+      //! \pre Called within `zone_->channels[channel_].strand`.
+      void operator()(boost::system::error_code error)
+      {
+        if (!zone_ || !zone_->p2p || zone_->noise.empty())
+          return;
+
+        if (error && error != boost::system::errc::operation_canceled)
+          throw boost::system::system_error{error, "send_noise timer failed"};
+
+        assert(zone_->channels.at(channel_).strand.running_in_this_thread());
+
+        const auto start = std::chrono::steady_clock::now();
+        noise_channel& channel = zone_->channels.at(channel_);
+
+        if (!channel.connection.is_nil())
+        {
+          epee::byte_slice message = nullptr;
+          if (!channel.active.empty())
+            message = channel.active.take_slice(zone_->noise.size());
+          else if (!channel.queue.empty())
+          {
+            channel.active = channel.queue.front().clone();
+            message = channel.active.take_slice(zone_->noise.size());
+          }
+          else
+            message = zone_->noise.clone();
+
+          if (zone_->p2p->send(std::move(message), channel.connection))
+          {
+            if (!channel.queue.empty() && channel.active.empty())
+              channel.queue.pop_front();
+          }
+          else
+          {
+            channel.active = nullptr;
+            channel.connection = boost::uuids::nil_uuid();
+            zone_->strand.post(
+              update_channels{zone_, get_out_connections(*zone_->p2p)}
+            );
+          }
+        }
+
+        wait(start, std::move(zone_), channel_);
+      }
+    };
+
+    //! Prepares connections for new channel epoch and sets timer for next epoch
+    struct start_epoch
+    {
+      // Variables allow for Dandelion++ extension
+      std::shared_ptr<detail::zone> zone_;
+      std::chrono::seconds min_epoch_;
+      std::chrono::seconds epoch_range_;
+      std::size_t count_;
+
+      //! \pre Should not be invoked within any strand to prevent blocking.
+      void operator()(const boost::system::error_code error = {})
+      {
+        if (!zone_ || !zone_->p2p)
+          return;
+
+        if (error && error != boost::system::errc::operation_canceled)
+          throw boost::system::system_error{error, "start_epoch timer failed"};
+
+        const auto start = std::chrono::steady_clock::now();
+        zone_->strand.dispatch(
+          change_channels{zone_, net::dandelionpp::connection_map{get_out_connections(*(zone_->p2p)), count_}}
+        );
+
+        detail::zone& alias = *zone_;
+        alias.next_epoch.expires_at(start + min_epoch_ + random_duration(epoch_range_));
+        alias.next_epoch.async_wait(start_epoch{std::move(*this)});
+      }
+    };
+  } // anonymous
+
+  notify::notify(boost::asio::io_service& service, std::shared_ptr<connections> p2p, epee::byte_slice noise)
+    : zone_(std::make_shared<detail::zone>(service, std::move(p2p), std::move(noise)))
+  {
+    if (!zone_->p2p)
+      throw std::logic_error{"cryptonote::levin::notify cannot have nullptr p2p argument"};
+
+    if (!zone_->noise.empty())
+    {
+      const auto now = std::chrono::steady_clock::now();
+      start_epoch{zone_, noise_min_epoch, noise_epoch_range, CRYPTONOTE_NOISE_CHANNELS}();
+      for (std::size_t channel = 0; channel < zone_->channels.size(); ++channel)
+        send_noise::wait(now, zone_, channel);
+    }
+  }
+
+  notify::~notify() noexcept
+  {}
+
+  notify::status notify::get_status() const noexcept
+  {
+    if (!zone_)
+      return {false, false};
+
+    return {!zone_->noise.empty(), CRYPTONOTE_NOISE_CHANNELS <= zone_->connection_count};
+  }
+
+  void notify::new_out_connection()
+  {
+    if (!zone_ || zone_->noise.empty() || CRYPTONOTE_NOISE_CHANNELS <= zone_->connection_count)
+      return;
+
+    zone_->strand.dispatch(
+      update_channels{zone_, get_out_connections(*(zone_->p2p))}
+    );
+  }
+
+  void notify::run_epoch()
+  {
+    if (!zone_)
+      return;
+    zone_->next_epoch.cancel();
+  }
+
+  void notify::run_stems()
+  {
+    if (!zone_)
+      return;
+
+    for (noise_channel& channel : zone_->channels)
+      channel.next_noise.cancel();
+  }
+
+  bool notify::send_txs(std::vector<cryptonote::blobdata> txs, const boost::uuids::uuid& source, const bool pad_txs)
+  {
+    if (!zone_)
+      return false;
+
+    if (!zone_->noise.empty() && !zone_->channels.empty())
+    {
+      // covert send in "noise" channel
+      static_assert(
+        CRYPTONOTE_MAX_FRAGMENTS * CRYPTONOTE_NOISE_BYTES <= LEVIN_DEFAULT_MAX_PACKET_SIZE, "most nodes will reject this fragment setting"
+      );
+
+      // padding is not useful when using noise mode
+      const std::string payload = make_tx_payload(std::move(txs), false);
+      epee::byte_slice message = epee::levin::make_fragmented_notify(
+        zone_->noise, NOTIFY_NEW_TRANSACTIONS::ID, epee::strspan<std::uint8_t>(payload)
+      );
+      if (CRYPTONOTE_MAX_FRAGMENTS * zone_->noise.size() < message.size())
+      {
+        MERROR("notify::send_txs provided message exceeding covert fragment size");
+        return false;
+      }
+
+      for (std::size_t channel = 0; channel < zone_->channels.size(); ++channel)
+      {
+        zone_->channels[channel].strand.dispatch(
+          queue_covert_notify{zone_, message.clone(), channel}
+        );
+      }
+    }
+    else
+    {
+      const std::string payload = make_tx_payload(std::move(txs), pad_txs);
+      epee::byte_slice message =
+        epee::levin::make_notify(NOTIFY_NEW_TRANSACTIONS::ID, epee::strspan<std::uint8_t>(payload));
+
+      // traditional monero send technique
+      zone_->strand.dispatch(flood_notify{zone_, std::move(message), source});
+    }
+
+    return true;
+  }
+} // levin
+} // net
diff --git a/src/cryptonote_protocol/levin_notify.h b/src/cryptonote_protocol/levin_notify.h
new file mode 100644
index 000000000..82d22680a
--- /dev/null
+++ b/src/cryptonote_protocol/levin_notify.h
@@ -0,0 +1,132 @@
+// Copyright (c) 2019, The Monero Project
+//
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright 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 IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#pragma once
+
+#include <boost/asio/io_service.hpp>
+#include <boost/uuid/uuid.hpp>
+#include <memory>
+#include <vector>
+
+#include "byte_slice.h"
+#include "cryptonote_basic/blobdatatype.h"
+#include "net/enums.h"
+#include "span.h"
+
+namespace epee
+{
+namespace levin
+{
+    template<typename> class async_protocol_handler_config;
+}
+}
+
+namespace nodetool
+{
+  template<typename> struct p2p_connection_context_t;
+}
+
+namespace cryptonote
+{
+  struct cryptonote_connection_context;
+}
+
+namespace cryptonote
+{
+namespace levin
+{
+  namespace detail
+  {
+    using p2p_context = nodetool::p2p_connection_context_t<cryptonote::cryptonote_connection_context>;
+    struct zone; //!< Internal data needed for zone notifications
+  } // detail
+
+  using connections = epee::levin::async_protocol_handler_config<detail::p2p_context>;
+
+  //! Provides tx notification privacy
+  class notify
+  {
+    std::shared_ptr<detail::zone> zone_;
+
+  public:
+    struct status
+    {
+      bool has_noise;
+      bool connections_filled;
+    };
+
+    //! Construct an instance that cannot notify.
+    notify() noexcept
+      : zone_(nullptr)
+    {}
+
+    //! Construct an instance with available notification `zones`.
+    explicit notify(boost::asio::io_service& service, std::shared_ptr<connections> p2p, epee::byte_slice noise);
+
+    notify(const notify&) = delete;
+    notify(notify&&) = default;
+
+    ~notify() noexcept;
+
+    notify& operator=(const notify&) = delete;
+    notify& operator=(notify&&) = default;
+
+    //! \return Status information for zone selection.
+    status get_status() const noexcept;
+
+    //! Probe for new outbound connection - skips if not needed.
+    void new_out_connection();
+
+    //! Run the logic for the next epoch immediately. Only use in testing.
+    void run_epoch();
+
+    //! Run the logic for the next stem timeout imemdiately. Only use in  testing.
+    void run_stems();
+
+    /*! Send txs using `cryptonote_protocol_defs.h` payload format wrapped in a
+        levin header. The message will be sent in a "discreet" manner if
+        enabled - if `!noise.empty()` then the `command`/`payload` will be
+        queued to send at the next available noise interval. Otherwise, a
+        standard Monero flood notification will be used.
+
+        \note Eventually Dandelion++ stem sending will be used here when
+          enabled.
+
+        \param txs The transactions that need to be serialized and relayed.
+        \param source The source of the notification. `is_nil()` indicates this
+          node is the source. Dandelion++ will use this to map a source to a
+          particular stem.
+        \param pad_txs A request to pad txs to help conceal origin via
+          statistical analysis. Ignored if noise was enabled during
+          construction.
+
+      \return True iff the notification is queued for sending. */
+    bool send_txs(std::vector<blobdata> txs, const boost::uuids::uuid& source, bool pad_txs);
+  };
+} // levin
+} // net