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)

12 files changed, 1156 insertions, 79 deletions

diff --git a/src/cryptonote_basic/connection_context.h b/src/cryptonote_basic/connection_context.h
index 96398a90b..51076e8c0 100644
--- a/src/cryptonote_basic/connection_context.h
+++ b/src/cryptonote_basic/connection_context.h
@@ -31,8 +31,10 @@
 #pragma once
 #include <unordered_set>
 #include <atomic>
+#include <boost/date_time/posix_time/posix_time.hpp>
 #include "net/net_utils_base.h"
 #include "copyable_atomic.h"
+#include "crypto/hash.h"
 
 namespace cryptonote
 {
diff --git a/src/cryptonote_config.h b/src/cryptonote_config.h
index b68bb41e1..173b454f6 100644
--- a/src/cryptonote_config.h
+++ b/src/cryptonote_config.h
@@ -100,6 +100,16 @@
 #define CRYPTONOTE_MEMPOOL_TX_LIVETIME                    (86400*3) //seconds, three days
 #define CRYPTONOTE_MEMPOOL_TX_FROM_ALT_BLOCK_LIVETIME     604800 //seconds, one week
 
+// see src/cryptonote_protocol/levin_notify.cpp
+#define CRYPTONOTE_NOISE_MIN_EPOCH                      5      // minutes
+#define CRYPTONOTE_NOISE_EPOCH_RANGE                    30     // seconds
+#define CRYPTONOTE_NOISE_MIN_DELAY                      10     // seconds
+#define CRYPTONOTE_NOISE_DELAY_RANGE                    5      // seconds
+#define CRYPTONOTE_NOISE_BYTES                          3*1024 // 3 KiB
+#define CRYPTONOTE_NOISE_CHANNELS                       2      // Max outgoing connections per zone used for noise/covert sending
+
+#define CRYPTONOTE_MAX_FRAGMENTS                        20 // ~20 * NOISE_BYTES max payload size for covert/noise send
+
 #define COMMAND_RPC_GET_BLOCKS_FAST_MAX_COUNT           1000
 
 #define P2P_LOCAL_WHITE_PEERLIST_LIMIT                  1000
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
diff --git a/src/net/CMakeLists.txt b/src/net/CMakeLists.txt
index 738f858f0..24b707f77 100644
--- a/src/net/CMakeLists.txt
+++ b/src/net/CMakeLists.txt
@@ -26,8 +26,8 @@
 # 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.
 
-set(net_sources error.cpp i2p_address.cpp parse.cpp socks.cpp socks_connect.cpp tor_address.cpp)
-set(net_headers error.h i2p_address.h parse.h socks.h socks_connect.h tor_address.h)
+set(net_sources dandelionpp.cpp error.cpp i2p_address.cpp parse.cpp socks.cpp socks_connect.cpp tor_address.cpp)
+set(net_headers dandelionpp.h error.h i2p_address.h parse.h socks.h socks_connect.h tor_address.h)
 
 monero_add_library(net ${net_sources} ${net_headers})
 target_link_libraries(net common epee ${Boost_ASIO_LIBRARY})
diff --git a/src/net/dandelionpp.cpp b/src/net/dandelionpp.cpp
new file mode 100644
index 000000000..4d2f75428
--- /dev/null
+++ b/src/net/dandelionpp.cpp
@@ -0,0 +1,212 @@
+// 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 "dandelionpp.h"
+
+#include <boost/container/small_vector.hpp>
+#include <boost/uuid/nil_generator.hpp>
+#include <chrono>
+
+#include "common/expect.h"
+#include "cryptonote_config.h"
+#include "crypto/crypto.h"
+
+namespace net
+{
+namespace dandelionpp
+{
+    namespace
+    {
+        constexpr const std::size_t expected_max_channels = CRYPTONOTE_NOISE_CHANNELS;
+
+        // could be in util somewhere
+        struct key_less
+        {
+            template<typename K, typename V>
+            bool operator()(const std::pair<K, V>& left, const K& right) const
+            {
+                return left.first < right;
+            }
+
+            template<typename K, typename V>
+            bool operator()(const K& left, const std::pair<K, V>& right) const
+            {
+                return left < right.first;
+            }
+        };
+
+        std::size_t select_stem(epee::span<const std::size_t> usage, epee::span<const boost::uuids::uuid> out_map)
+        {
+            assert(usage.size() < std::numeric_limits<std::size_t>::max()); // prevented in constructor
+            if (usage.size() < out_map.size())
+                return std::numeric_limits<std::size_t>::max();
+
+            // small_vector uses stack space if `expected_max_channels < capacity()`
+            std::size_t lowest = std::numeric_limits<std::size_t>::max();
+            boost::container::small_vector<std::size_t, expected_max_channels> choices;
+            static_assert(sizeof(choices) < 256, "choices is too large based on current configuration");
+
+            for (const boost::uuids::uuid& out : out_map)
+            {
+                if (!out.is_nil())
+                {
+                    const std::size_t location = std::addressof(out) - out_map.begin();
+                    if (usage[location] < lowest)
+                    {
+                        lowest = usage[location];
+                        choices = {location};
+                    }
+                    else if (usage[location] == lowest)
+                        choices.push_back(location);
+                }
+            }
+
+            switch (choices.size())
+            {
+            case 0:
+                return std::numeric_limits<std::size_t>::max();
+            case 1:
+                return choices[0];
+            default:
+                break;
+            }
+
+            return choices[crypto::rand_idx(choices.size())];
+        }
+    } // anonymous
+
+    connection_map::connection_map(std::vector<boost::uuids::uuid> out_connections, const std::size_t stems)
+      : out_mapping_(std::move(out_connections)),
+        in_mapping_(),
+        usage_count_()
+    {
+        // max value is used by `select_stem` as error case
+        if (stems == std::numeric_limits<std::size_t>::max())
+            MONERO_THROW(common_error::kInvalidArgument, "stems value cannot be max size_t");
+
+        usage_count_.resize(stems);
+        if (stems < out_mapping_.size())
+        {
+            for (unsigned i = 0; i < stems; ++i)
+                std::swap(out_mapping_[i], out_mapping_.at(i + crypto::rand_idx(out_mapping_.size() - i)));
+
+            out_mapping_.resize(stems);
+        }
+        else
+        {
+            std::shuffle(out_mapping_.begin(), out_mapping_.end(), crypto::random_device{});
+        }
+    }
+
+    connection_map::~connection_map() noexcept
+    {}
+
+    connection_map connection_map::clone() const
+    {
+        return {*this};
+    }
+
+    bool connection_map::update(std::vector<boost::uuids::uuid> current)
+    {
+        std::sort(current.begin(), current.end());
+
+        bool replace = false;
+        for (auto& existing_out : out_mapping_)
+        {
+            const auto elem = std::lower_bound(current.begin(), current.end(), existing_out);
+            if (elem == current.end() || *elem != existing_out)
+            {
+                existing_out = boost::uuids::nil_uuid();
+                replace = true;
+            }
+            else // already using connection, remove it from candidate list
+                current.erase(elem);
+        }
+
+        if (!replace && out_mapping_.size() == usage_count_.size())
+            return false;
+
+        const std::size_t existing_outs = out_mapping_.size();
+        for (std::size_t i = 0; i < usage_count_.size() && !current.empty(); ++i)
+        {
+            const bool increase_stems = out_mapping_.size() <= i;
+            if (increase_stems || out_mapping_[i].is_nil())
+            {
+                std::swap(current.back(), current.at(crypto::rand_idx(current.size())));
+                if (increase_stems)
+                    out_mapping_.push_back(current.back());
+                else
+                    out_mapping_[i] = current.back();
+                current.pop_back();
+            }
+        }
+
+        return replace || existing_outs < out_mapping_.size();
+    }
+
+    std::size_t connection_map::size() const noexcept
+    {
+        std::size_t count = 0;
+        for (const boost::uuids::uuid& connection : out_mapping_)
+        {
+            if (!connection.is_nil())
+                ++count;
+        }
+        return count;
+    }
+
+    boost::uuids::uuid connection_map::get_stem(const boost::uuids::uuid& source)
+    {
+        auto elem = std::lower_bound(in_mapping_.begin(), in_mapping_.end(), source, key_less{});
+        if (elem == in_mapping_.end() || elem->first != source)
+        {
+            const std::size_t index = select_stem(epee::to_span(usage_count_), epee::to_span(out_mapping_));
+            if (out_mapping_.size() < index)
+                return boost::uuids::nil_uuid();
+
+            elem = in_mapping_.emplace(elem, source, index);
+            usage_count_[index]++;
+        }
+        else if (out_mapping_.at(elem->second).is_nil()) // stem connection disconnected after mapping
+        {
+            usage_count_.at(elem->second)--;
+            const std::size_t index = select_stem(epee::to_span(usage_count_), epee::to_span(out_mapping_));
+            if (out_mapping_.size() < index)
+            {
+                in_mapping_.erase(elem);
+                return boost::uuids::nil_uuid();
+            }
+
+            elem->second = index;
+            usage_count_[index]++;
+        }
+
+        return out_mapping_[elem->second];
+    }
+} // dandelionpp
+} // net
diff --git a/src/net/dandelionpp.h b/src/net/dandelionpp.h
new file mode 100644
index 000000000..75b63bc0c
--- /dev/null
+++ b/src/net/dandelionpp.h
@@ -0,0 +1,106 @@
+// 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/uuid/uuid.hpp>
+#include <cstddef>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "span.h"
+
+namespace net
+{
+namespace dandelionpp
+{
+    //! Assists with mapping source -> stem and tracking connections for stem.
+    class connection_map
+    {
+        // Make sure to update clone method if changing members
+        std::vector<boost::uuids::uuid> out_mapping_; //<! Current outgoing uuid connection at index.
+        std::vector<std::pair<boost::uuids::uuid, std::size_t>> in_mapping_; //<! uuid source to an `out_mapping_` index.
+        std::vector<std::size_t> usage_count_;
+
+        // Use clone method to prevent "hidden" copies.
+        connection_map(const connection_map&) = default;
+
+    public:
+        using value_type = boost::uuids::uuid;
+        using size_type = std::vector<boost::uuids::uuid>::size_type;
+        using difference_type = std::vector<boost::uuids::uuid>::difference_type;
+        using reference = const boost::uuids::uuid&;
+        using const_reference = reference;
+        using iterator = std::vector<boost::uuids::uuid>::const_iterator;
+        using const_iterator = iterator;
+
+        //! Initialized with zero stem connections.
+        explicit connection_map()
+          : connection_map(std::vector<boost::uuids::uuid>{}, 0)
+        {}
+
+        //! Initialized with `out_connections` and `stem_count`.
+        explicit connection_map(std::vector<boost::uuids::uuid> out_connections, std::size_t stems);
+
+        connection_map(connection_map&&) = default;
+        ~connection_map() noexcept;
+        connection_map& operator=(connection_map&&) = default;
+        connection_map& operator=(const connection_map&) = delete;
+
+        //! \return An exact duplicate of `this` map.
+        connection_map clone() const;
+
+        //! \return First stem connection.
+        const_iterator begin() const noexcept
+        {
+            return out_mapping_.begin();
+        }
+
+        //! \return One-past the last stem connection.
+        const_iterator end() const noexcept
+        {
+            return out_mapping_.end();
+        }
+
+        /*! Merges in current connections with the previous set of connections.
+            If a connection died, a new one will take its place in the stem or
+            the stem is marked as dead.
+
+            \param connections Current outbound connection ids.
+            \return True if any updates to `get_connections()` was made. */
+        bool update(std::vector<boost::uuids::uuid> current);
+
+        //! \return Number of outgoing connections in use.
+        std::size_t size() const noexcept;
+
+        //! \return Current stem mapping for `source` or `nil_uuid()` if none is possible.
+        boost::uuids::uuid get_stem(const boost::uuids::uuid& source);
+    };
+} // dandelionpp
+} // net
diff --git a/src/p2p/net_node.cpp b/src/p2p/net_node.cpp
index bb51be242..c7fc058ca 100644
--- a/src/p2p/net_node.cpp
+++ b/src/p2p/net_node.cpp
@@ -144,7 +144,7 @@ namespace nodetool
     const command_line::arg_descriptor<std::vector<std::string> > arg_p2p_add_exclusive_node   = {"add-exclusive-node", "Specify list of peers to connect to only."
                                                                                                   " If this option is given the options add-priority-node and seed-node are ignored"};
     const command_line::arg_descriptor<std::vector<std::string> > arg_p2p_seed_node   = {"seed-node", "Connect to a node to retrieve peer addresses, and disconnect"};
-    const command_line::arg_descriptor<std::vector<std::string> > arg_proxy = {"proxy", "<network-type>,<socks-ip:port>[,max_connections] i.e. \"tor,127.0.0.1:9050,100\""};
+    const command_line::arg_descriptor<std::vector<std::string> > arg_proxy = {"proxy", "<network-type>,<socks-ip:port>[,max_connections][,disable_noise] i.e. \"tor,127.0.0.1:9050,100,disable_noise\""};
     const command_line::arg_descriptor<std::vector<std::string> > arg_anonymous_inbound = {"anonymous-inbound", "<hidden-service-address>,<[bind-ip:]port>[,max_connections] i.e. \"x.onion,127.0.0.1:18083,100\""};
     const command_line::arg_descriptor<bool> arg_p2p_hide_my_port   =    {"hide-my-port", "Do not announce yourself as peerlist candidate", false, true};
     const command_line::arg_descriptor<bool> arg_no_sync = {"no-sync", "Don't synchronize the blockchain with other peers", false};
@@ -163,7 +163,7 @@ namespace nodetool
 
     boost::optional<std::vector<proxy>> get_proxies(boost::program_options::variables_map const& vm)
     {
-	namespace ip = boost::asio::ip;
+        namespace ip = boost::asio::ip;
 
         std::vector<proxy> proxies{};
 
@@ -183,14 +183,25 @@ namespace nodetool
             const boost::string_ref proxy{next->begin(), next->size()};
 
             ++next;
-            if (!next.eof())
+            for (unsigned count = 0; !next.eof(); ++count, ++next)
             {
-                proxies.back().max_connections = get_max_connections(*next);
-                if (proxies.back().max_connections == 0)
+                if (2 <= count)
                 {
-                    MERROR("Invalid max connections given to --" << arg_proxy.name);
+                    MERROR("Too many ',' characters given to --" << arg_proxy.name);
                     return boost::none;
                 }
+
+                if (boost::string_ref{next->begin(), next->size()} == "disable_noise")
+                    proxies.back().noise = false;
+                else
+                {
+                    proxies.back().max_connections = get_max_connections(*next);
+                    if (proxies.back().max_connections == 0)
+                    {
+                        MERROR("Invalid max connections given to --" << arg_proxy.name);
+                        return boost::none;
+                    }
+                }
             }
 
             switch (epee::net_utils::zone_from_string(zone))
@@ -214,7 +225,7 @@ namespace nodetool
                 return boost::none;
             }
             proxies.back().address = ip::tcp::endpoint{ip::address_v4{boost::endian::native_to_big(ip)}, port};
-	}
+        }
 
         return proxies;
     }
diff --git a/src/p2p/net_node.h b/src/p2p/net_node.h
index 6d2ae878f..231175dd2 100644
--- a/src/p2p/net_node.h
+++ b/src/p2p/net_node.h
@@ -43,6 +43,7 @@
 #include <vector>
 
 #include "cryptonote_config.h"
+#include "cryptonote_protocol/levin_notify.h"
 #include "warnings.h"
 #include "net/abstract_tcp_server2.h"
 #include "net/levin_protocol_handler.h"
@@ -66,12 +67,14 @@ namespace nodetool
     proxy()
       : max_connections(-1),
         address(),
-        zone(epee::net_utils::zone::invalid)
+        zone(epee::net_utils::zone::invalid),
+        noise(true)
     {}
 
     std::int64_t max_connections;
     boost::asio::ip::tcp::endpoint address;
     epee::net_utils::zone zone;
+    bool noise;
   };
 
   struct anonymous_inbound
@@ -154,6 +157,7 @@ namespace nodetool
           m_bind_ipv6_address(),
           m_port(),
           m_port_ipv6(),
+          m_notifier(),
           m_our_address(),
           m_peerlist(),
           m_config{},
@@ -172,6 +176,7 @@ namespace nodetool
           m_bind_ipv6_address(),
           m_port(),
           m_port_ipv6(),
+          m_notifier(),
           m_our_address(),
           m_peerlist(),
           m_config{},
@@ -189,6 +194,7 @@ namespace nodetool
       std::string m_bind_ipv6_address;
       std::string m_port;
       std::string m_port_ipv6;
+      cryptonote::levin::notify m_notifier;
       epee::net_utils::network_address m_our_address; // in anonymity networks
       peerlist_manager m_peerlist;
       config m_config;
@@ -255,7 +261,6 @@ namespace nodetool
     size_t get_public_gray_peers_count();
     void get_public_peerlist(std::vector<peerlist_entry>& gray, std::vector<peerlist_entry>& white);
     void get_peerlist(std::vector<peerlist_entry>& gray, std::vector<peerlist_entry>& white);
-    size_t get_zone_count() const { return m_network_zones.size(); }
 
     void change_max_out_public_peers(size_t count);
     uint32_t get_max_out_public_peers() const;
@@ -330,6 +335,7 @@ namespace nodetool
     virtual void callback(p2p_connection_context& context);
     //----------------- i_p2p_endpoint -------------------------------------------------------------
     virtual bool relay_notify_to_list(int command, const epee::span<const uint8_t> data_buff, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections);
+    virtual epee::net_utils::zone send_txs(std::vector<cryptonote::blobdata> txs, const epee::net_utils::zone origin, const boost::uuids::uuid& source, const bool pad_txs);
     virtual bool invoke_command_to_peer(int command, const epee::span<const uint8_t> req_buff, std::string& resp_buff, const epee::net_utils::connection_context_base& context);
     virtual bool invoke_notify_to_peer(int command, const epee::span<const uint8_t> req_buff, const epee::net_utils::connection_context_base& context);
     virtual bool drop_connection(const epee::net_utils::connection_context_base& context);
diff --git a/src/p2p/net_node.inl b/src/p2p/net_node.inl
index 8c0cff7e2..41ca19917 100644
--- a/src/p2p/net_node.inl
+++ b/src/p2p/net_node.inl
@@ -383,6 +383,9 @@ namespace nodetool
     m_offline = command_line::get_arg(vm, cryptonote::arg_offline);
     m_use_ipv6 = command_line::get_arg(vm, arg_p2p_use_ipv6);
     m_require_ipv4 = command_line::get_arg(vm, arg_p2p_require_ipv4);
+    public_zone.m_notifier = cryptonote::levin::notify{
+      public_zone.m_net_server.get_io_service(), public_zone.m_net_server.get_config_shared(), nullptr
+    };
 
     if (command_line::has_arg(vm, arg_p2p_add_peer))
     {
@@ -462,6 +465,7 @@ namespace nodetool
       return false;
 
 
+    epee::byte_slice noise = nullptr;
     auto proxies = get_proxies(vm);
     if (!proxies)
       return false;
@@ -479,6 +483,20 @@ namespace nodetool
 
       if (!set_max_out_peers(zone, proxy.max_connections))
         return false;
+
+      epee::byte_slice this_noise = nullptr;
+      if (proxy.noise)
+      {
+        static_assert(sizeof(epee::levin::bucket_head2) < CRYPTONOTE_NOISE_BYTES, "noise bytes too small");
+        if (noise.empty())
+          noise = epee::levin::make_noise_notify(CRYPTONOTE_NOISE_BYTES);
+
+        this_noise = noise.clone();
+      }
+
+      zone.m_notifier = cryptonote::levin::notify{
+        zone.m_net_server.get_io_service(), zone.m_net_server.get_config_shared(), std::move(this_noise)
+      };
     }
 
     for (const auto& zone : m_network_zones)
@@ -494,6 +512,7 @@ namespace nodetool
     if (!inbounds)
       return false;
 
+    const std::size_t tx_relay_zones = m_network_zones.size();
     for (auto& inbound : *inbounds)
     {
       network_zone& zone = add_zone(inbound.our_address.get_zone());
@@ -504,6 +523,12 @@ namespace nodetool
         return false;
       }
 
+      if (zone.m_connect == nullptr && tx_relay_zones <= 1)
+      {
+        MERROR("Listed --" << arg_anonymous_inbound.name << " without listing any --" << arg_proxy.name << ". The latter is necessary for sending origin txes over anonymity networks");
+        return false;
+      }
+
       zone.m_bind_ip = std::move(inbound.local_ip);
       zone.m_port = std::move(inbound.local_port);
       zone.m_net_server.set_default_remote(std::move(inbound.default_remote));
@@ -1266,6 +1291,7 @@ namespace nodetool
     ape.first_seen = first_seen_stamp ? first_seen_stamp : time(nullptr);
 
     zone.m_peerlist.append_with_peer_anchor(ape);
+    zone.m_notifier.new_out_connection();
 
     LOG_DEBUG_CC(*con, "CONNECTION HANDSHAKED OK.");
     return true;
@@ -1990,7 +2016,7 @@ namespace nodetool
         }
         if (c_id.first <= zone->first)
           break;
-	  
+
         ++zone;
       }
       if (zone->first == c_id.first)
@@ -2000,6 +2026,61 @@ namespace nodetool
   }
   //-----------------------------------------------------------------------------------
   template<class t_payload_net_handler>
+  epee::net_utils::zone node_server<t_payload_net_handler>::send_txs(std::vector<cryptonote::blobdata> txs, const epee::net_utils::zone origin, const boost::uuids::uuid& source, const bool pad_txs)
+  {
+    namespace enet = epee::net_utils;
+
+    const auto send = [&txs, &source, pad_txs] (std::pair<const enet::zone, network_zone>& network)
+    {
+      if (network.second.m_notifier.send_txs(std::move(txs), source, (pad_txs || network.first != enet::zone::public_)))
+        return network.first;
+      return enet::zone::invalid;
+    };
+
+    if (m_network_zones.empty())
+      return enet::zone::invalid;
+
+    if (origin != enet::zone::invalid)
+      return send(*m_network_zones.begin()); // send all txs received via p2p over public network
+
+    if (m_network_zones.size() <= 2)
+      return send(*m_network_zones.rbegin()); // see static asserts below; sends over anonymity network iff enabled
+
+    /* These checks are to ensure that i2p is highest priority if multiple
+       zones are selected. Make sure to update logic if the values cannot be
+       in the same relative order. `m_network_zones` must be sorted map too. */
+    static_assert(std::is_same<std::underlying_type<enet::zone>::type, std::uint8_t>{}, "expected uint8_t zone");
+    static_assert(unsigned(enet::zone::invalid) == 0, "invalid expected to be 0");
+    static_assert(unsigned(enet::zone::public_) == 1, "public_ expected to be 1");
+    static_assert(unsigned(enet::zone::i2p) == 2, "i2p expected to be 2");
+    static_assert(unsigned(enet::zone::tor) == 3, "tor expected to be 3");
+
+    // check for anonymity networks with noise and connections
+    for (auto network = ++m_network_zones.begin(); network != m_network_zones.end(); ++network)
+    {
+      if (enet::zone::tor < network->first)
+        break; // unknown network
+
+      const auto status = network->second.m_notifier.get_status();
+      if (status.has_noise && status.connections_filled)
+        return send(*network);
+    }
+
+    // use the anonymity network with outbound support
+    for (auto network = ++m_network_zones.begin(); network != m_network_zones.end(); ++network)
+    {
+      if (enet::zone::tor < network->first)
+        break; // unknown network
+
+      if (network->second.m_connect)
+        return send(*network);
+    }
+
+    // configuration should not allow this scenario
+    return enet::zone::invalid;
+  }
+  //-----------------------------------------------------------------------------------
+  template<class t_payload_net_handler>
   void node_server<t_payload_net_handler>::callback(p2p_connection_context& context)
   {
     m_payload_handler.on_callback(context);
diff --git a/src/p2p/net_node_common.h b/src/p2p/net_node_common.h
index 34d151f5f..239814c2c 100644
--- a/src/p2p/net_node_common.h
+++ b/src/p2p/net_node_common.h
@@ -33,6 +33,8 @@
 #include <boost/uuid/uuid.hpp>
 #include <utility>
 #include <vector>
+#include "cryptonote_basic/blobdatatype.h"
+#include "net/enums.h"
 #include "net/net_utils_base.h"
 #include "p2p_protocol_defs.h"
 
@@ -46,12 +48,12 @@ namespace nodetool
   struct i_p2p_endpoint
   {
     virtual bool relay_notify_to_list(int command, const epee::span<const uint8_t> data_buff, std::vector<std::pair<epee::net_utils::zone, boost::uuids::uuid>> connections)=0;
+    virtual epee::net_utils::zone send_txs(std::vector<cryptonote::blobdata> txs, const epee::net_utils::zone origin, const boost::uuids::uuid& source, const bool pad_txs)=0;
     virtual bool invoke_command_to_peer(int command, const epee::span<const uint8_t> req_buff, std::string& resp_buff, const epee::net_utils::connection_context_base& context)=0;
     virtual bool invoke_notify_to_peer(int command, const epee::span<const uint8_t> req_buff, const epee::net_utils::connection_context_base& context)=0;
     virtual bool drop_connection(const epee::net_utils::connection_context_base& context)=0;
     virtual void request_callback(const epee::net_utils::connection_context_base& context)=0;
     virtual uint64_t get_public_connections_count()=0;
-    virtual size_t get_zone_count() const=0;
     virtual void for_each_connection(std::function<bool(t_connection_context&, peerid_type, uint32_t)> f)=0;
     virtual bool for_connection(const boost::uuids::uuid&, std::function<bool(t_connection_context&, peerid_type, uint32_t)> f)=0;
     virtual bool block_host(const epee::net_utils::network_address &address, time_t seconds = 0)=0;
@@ -71,6 +73,10 @@ namespace nodetool
     {
       return false;
     }
+    virtual epee::net_utils::zone send_txs(std::vector<cryptonote::blobdata> txs, const epee::net_utils::zone origin, const boost::uuids::uuid& source, const bool pad_txs)
+    {
+      return epee::net_utils::zone::invalid;
+    }
     virtual bool invoke_command_to_peer(int command, const epee::span<const uint8_t> req_buff, std::string& resp_buff, const epee::net_utils::connection_context_base& context)
     {
       return false;
@@ -96,11 +102,6 @@ namespace nodetool
       return false;
     }
 
-    virtual size_t get_zone_count() const
-    {
-      return 0;
-    }
-
     virtual uint64_t get_public_connections_count()    
     {
       return false;