Add randomized delay when forwarding txes from i2p/tor -> ipv4/6

8 files changed, 122 insertions, 32 deletions

diff --git a/src/blockchain_db/blockchain_db.cpp b/src/blockchain_db/blockchain_db.cpp
index 01faf43c4..336577a07 100644
--- a/src/blockchain_db/blockchain_db.cpp
+++ b/src/blockchain_db/blockchain_db.cpp
@@ -63,6 +63,7 @@ bool matches_category(relay_method method, relay_category category) noexcept
   {
     default:
     case relay_method::local:
+    case relay_method::forward:
     case relay_method::stem:
       return false;
     case relay_method::block:
@@ -79,6 +80,7 @@ void txpool_tx_meta_t::set_relay_method(relay_method method) noexcept
   kept_by_block = 0;
   do_not_relay = 0;
   is_local = 0;
+  is_forwarding = 0;
   dandelionpp_stem = 0;
 
   switch (method)
@@ -89,8 +91,8 @@ void txpool_tx_meta_t::set_relay_method(relay_method method) noexcept
     case relay_method::local:
       is_local = 1;
       break;
-    default:
-    case relay_method::fluff:
+    case relay_method::forward:
+      is_forwarding = 1;
       break;
     case relay_method::stem:
       dandelionpp_stem = 1;
@@ -98,26 +100,45 @@ void txpool_tx_meta_t::set_relay_method(relay_method method) noexcept
     case relay_method::block:
       kept_by_block = 1;
       break;
+    default:
+    case relay_method::fluff:
+      break;
   }
 }
 
 relay_method txpool_tx_meta_t::get_relay_method() const noexcept
 {
-  if (kept_by_block)
-    return relay_method::block;
-  if (do_not_relay)
-    return relay_method::none;
-  if (is_local)
-    return relay_method::local;
-  if (dandelionpp_stem)
-    return relay_method::stem;
+  const uint8_t state =
+    uint8_t(kept_by_block) +
+    (uint8_t(do_not_relay) << 1) +
+    (uint8_t(is_local) << 2) +
+    (uint8_t(is_forwarding) << 3) +
+    (uint8_t(dandelionpp_stem) << 4);
+
+  switch (state)
+  {
+    default: // error case
+    case 0:
+      break;
+    case 1:
+      return relay_method::block;
+    case 2:
+      return relay_method::none;
+    case 4:
+      return relay_method::local;
+    case 8:
+      return relay_method::forward;
+    case 16:
+      return relay_method::stem;
+  };
   return relay_method::fluff;
 }
 
 bool txpool_tx_meta_t::upgrade_relay_method(relay_method method) noexcept
 {
   static_assert(relay_method::none < relay_method::local, "bad relay_method value");
-  static_assert(relay_method::local < relay_method::stem, "bad relay_method value");
+  static_assert(relay_method::local < relay_method::forward, "bad relay_method value");
+  static_assert(relay_method::forward < relay_method::stem, "bad relay_method value");
   static_assert(relay_method::stem < relay_method::fluff, "bad relay_method value");
   static_assert(relay_method::fluff < relay_method::block, "bad relay_method value");
 
diff --git a/src/blockchain_db/blockchain_db.h b/src/blockchain_db/blockchain_db.h
index 3e2387da4..ac2c55db1 100644
--- a/src/blockchain_db/blockchain_db.h
+++ b/src/blockchain_db/blockchain_db.h
@@ -160,7 +160,7 @@ struct txpool_tx_meta_t
   uint64_t max_used_block_height;
   uint64_t last_failed_height;
   uint64_t receive_time;
-  uint64_t last_relayed_time; //!< If Dandelion++ stem, randomized embargo timestamp. Otherwise, last relayed timestmap.
+  uint64_t last_relayed_time; //!< If received over i2p/tor, randomized forward time. If Dandelion++stem, randomized embargo time. Otherwise, last relayed timestamp
   // 112 bytes
   uint8_t kept_by_block;
   uint8_t relayed;
@@ -169,7 +169,8 @@ struct txpool_tx_meta_t
   uint8_t pruned: 1;
   uint8_t is_local: 1;
   uint8_t dandelionpp_stem : 1;
-  uint8_t bf_padding: 4;
+  uint8_t is_forwarding: 1;
+  uint8_t bf_padding: 3;
 
   uint8_t padding[76]; // till 192 bytes
 
diff --git a/src/cryptonote_config.h b/src/cryptonote_config.h
index 81dc15dee..401cca1ca 100644
--- a/src/cryptonote_config.h
+++ b/src/cryptonote_config.h
@@ -117,6 +117,11 @@
 #define CRYPTONOTE_NOISE_BYTES                          3*1024 // 3 KiB
 #define CRYPTONOTE_NOISE_CHANNELS                       2      // Max outgoing connections per zone used for noise/covert sending
 
+// Both below are in seconds. The idea is to delay forwarding from i2p/tor
+// to ipv4/6, such that 2+ incoming connections _could_ have sent the tx
+#define CRYPTONOTE_FORWARD_DELAY_BASE (CRYPTONOTE_NOISE_MIN_DELAY + CRYPTONOTE_NOISE_DELAY_RANGE)
+#define CRYPTONOTE_FORWARD_DELAY_AVERAGE (CRYPTONOTE_FORWARD_DELAY_BASE + (CRYPTONOTE_FORWARD_DELAY_BASE / 2))
+
 #define CRYPTONOTE_MAX_FRAGMENTS                        20 // ~20 * NOISE_BYTES max payload size for covert/noise send
 
 #define COMMAND_RPC_GET_BLOCKS_FAST_MAX_COUNT           1000
diff --git a/src/cryptonote_core/cryptonote_core.cpp b/src/cryptonote_core/cryptonote_core.cpp
index 3ff3c77e2..521734bd2 100644
--- a/src/cryptonote_core/cryptonote_core.cpp
+++ b/src/cryptonote_core/cryptonote_core.cpp
@@ -1272,6 +1272,7 @@ namespace cryptonote
     {
       NOTIFY_NEW_TRANSACTIONS::request public_req{};
       NOTIFY_NEW_TRANSACTIONS::request private_req{};
+      NOTIFY_NEW_TRANSACTIONS::request stem_req{};
       for (auto& tx : txs)
       {
         switch (std::get<2>(tx))
@@ -1282,6 +1283,9 @@ namespace cryptonote
           case relay_method::local:
             private_req.txs.push_back(std::move(std::get<1>(tx)));
             break;
+          case relay_method::forward:
+            stem_req.txs.push_back(std::move(std::get<1>(tx)));
+            break;
           case relay_method::block:
           case relay_method::fluff:
           case relay_method::stem:
@@ -1299,6 +1303,8 @@ namespace cryptonote
         get_protocol()->relay_transactions(public_req, source, epee::net_utils::zone::public_, relay_method::fluff);
       if (!private_req.txs.empty())
         get_protocol()->relay_transactions(private_req, source, epee::net_utils::zone::invalid, relay_method::local);
+      if (!stem_req.txs.empty())
+        get_protocol()->relay_transactions(stem_req, source, epee::net_utils::zone::public_, relay_method::stem);
     }
     return true;
   }
diff --git a/src/cryptonote_core/tx_pool.cpp b/src/cryptonote_core/tx_pool.cpp
index a7b2e4422..542dbeb03 100644
--- a/src/cryptonote_core/tx_pool.cpp
+++ b/src/cryptonote_core/tx_pool.cpp
@@ -91,6 +91,8 @@ namespace cryptonote
     time_t const MAX_RELAY_TIME = (60 * 60 * 4); // at most that many seconds between resends
     float const ACCEPT_THRESHOLD = 1.0f;
 
+    constexpr const std::chrono::seconds forward_delay_average{CRYPTONOTE_FORWARD_DELAY_AVERAGE};
+
     // a kind of increasing backoff within min/max bounds
     uint64_t get_relay_delay(time_t now, time_t received)
     {
@@ -309,8 +311,14 @@ namespace cryptonote
 
         if (meta.upgrade_relay_method(tx_relay) || !existing_tx) // synchronize with embargo timer or stem/fluff out-of-order messages
         {
+          using clock = std::chrono::system_clock;
+          auto last_relayed_time = std::numeric_limits<decltype(meta.last_relayed_time)>::max();
+          if (tx_relay == relay_method::forward)
+            last_relayed_time = clock::to_time_t(clock::now() + crypto::random_poisson_seconds{forward_delay_average}());
+          // else the `set_relayed` function will adjust the time accordingly later
+
           //update transactions container
-          meta.last_relayed_time = std::numeric_limits<decltype(meta.last_relayed_time)>::max();
+          meta.last_relayed_time = last_relayed_time;
           meta.receive_time = receive_time;
           meta.weight = tx_weight;
           meta.fee = fee;
@@ -341,7 +349,7 @@ namespace cryptonote
       tvc.m_added_to_pool = true;
 
       static_assert(unsigned(relay_method::none) == 0, "expected relay_method::none value to be zero");
-      if(meta.fee > 0)
+      if(meta.fee > 0 && tx_relay != relay_method::forward)
         tvc.m_relay = tx_relay;
     }
 
@@ -722,28 +730,46 @@ namespace cryptonote
   //TODO: investigate whether boolean return is appropriate
   bool tx_memory_pool::get_relayable_transactions(std::vector<std::tuple<crypto::hash, cryptonote::blobdata, relay_method>> &txs) const
   {
+    std::vector<std::pair<crypto::hash, txpool_tx_meta_t>> change_timestamps;
+    const uint64_t now = time(NULL);
+
     CRITICAL_REGION_LOCAL(m_transactions_lock);
     CRITICAL_REGION_LOCAL1(m_blockchain);
-    const uint64_t now = time(NULL);
+    LockedTXN lock(m_blockchain.get_db());
     txs.reserve(m_blockchain.get_txpool_tx_count());
-    m_blockchain.for_all_txpool_txes([this, now, &txs](const crypto::hash &txid, const txpool_tx_meta_t &meta, const cryptonote::blobdata *){
+    m_blockchain.for_all_txpool_txes([this, now, &txs, &change_timestamps](const crypto::hash &txid, const txpool_tx_meta_t &meta, const cryptonote::blobdata *){
       // 0 fee transactions are never relayed
       if(!meta.pruned && meta.fee > 0 && !meta.do_not_relay)
       {
-        if (!meta.dandelionpp_stem && now - meta.last_relayed_time <= get_relay_delay(now, meta.receive_time))
-          return true;
-        if (meta.dandelionpp_stem && meta.last_relayed_time < now) // for dandelion++ stem, this value is the embargo timeout
-          return true;
+        const relay_method tx_relay = meta.get_relay_method();
+        switch (tx_relay)
+        {
+          case relay_method::stem:
+          case relay_method::forward:
+            if (meta.last_relayed_time > now)
+              return true; // continue to next tx
+            change_timestamps.emplace_back(txid, meta);
+            break;
+          default:
+          case relay_method::none:
+            return true;
+          case relay_method::local:
+          case relay_method::fluff:
+          case relay_method::block:
+            if (now - meta.last_relayed_time <= get_relay_delay(now, meta.receive_time))
+              return true; // continue to next tx
+            break;
+        }
 
         // if the tx is older than half the max lifetime, we don't re-relay it, to avoid a problem
         // mentioned by smooth where nodes would flush txes at slightly different times, causing
         // flushed txes to be re-added when received from a node which was just about to flush it
-        uint64_t max_age = meta.kept_by_block ? CRYPTONOTE_MEMPOOL_TX_FROM_ALT_BLOCK_LIVETIME : CRYPTONOTE_MEMPOOL_TX_LIVETIME;
+        uint64_t max_age = (tx_relay == relay_method::block) ? CRYPTONOTE_MEMPOOL_TX_FROM_ALT_BLOCK_LIVETIME : CRYPTONOTE_MEMPOOL_TX_LIVETIME;
         if (now - meta.receive_time <= max_age / 2)
         {
           try
           {
-            txs.emplace_back(txid, m_blockchain.get_txpool_tx_blob(txid, relay_category::all), meta.get_relay_method());
+            txs.emplace_back(txid, m_blockchain.get_txpool_tx_blob(txid, relay_category::all), tx_relay);
           }
           catch (const std::exception &e)
           {
@@ -754,6 +780,18 @@ namespace cryptonote
       }
       return true;
     }, false, relay_category::relayable);
+
+    for (auto& elem : change_timestamps)
+    {
+      /* These transactions are still in forward or stem state, so the field
+         represents the next time a relay should be attempted. Will be
+         overwritten when the state is upgraded to stem, fluff or block. This
+         function is only called every ~2 minutes, so this resetting should be
+         unnecessary, but is primarily a precaution against potential changes
+	 to the callback routines. */
+      elem.second.last_relayed_time = now + get_relay_delay(now, elem.second.receive_time);
+      m_blockchain.update_txpool_tx(elem.first, elem.second);
+    }
     return true;
   }
   //---------------------------------------------------------------------------------
diff --git a/src/cryptonote_protocol/cryptonote_protocol_handler.inl b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
index f8e032fde..ef3ea837d 100644
--- a/src/cryptonote_protocol/cryptonote_protocol_handler.inl
+++ b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
@@ -927,7 +927,19 @@ namespace cryptonote
       return 1;
     }
 
-    relay_method tx_relay;
+    /* If the txes were received over i2p/tor, the default is to "forward"
+       with a randomized delay to further enhance the "white noise" behavior,
+       potentially making it harder for ISP-level spies to determine which
+       inbound link sent the tx. If the sender disabled "white noise" over
+       i2p/tor, then the sender is "fluffing" (to only outbound) i2p/tor
+       connections with the `dandelionpp_fluff` flag set. The receiver (hidden
+       service) will immediately fluff in that scenario (i.e. this assumes that a
+       sybil spy will be unable to link an IP to an i2p/tor connection). */
+
+    const epee::net_utils::zone zone = context.m_remote_address.get_zone();
+    relay_method tx_relay = zone == epee::net_utils::zone::public_ ?
+      relay_method::stem : relay_method::forward;
+
     std::vector<blobdata> stem_txs{};
     std::vector<blobdata> fluff_txs{};
     if (arg.dandelionpp_fluff)
@@ -936,10 +948,7 @@ namespace cryptonote
       fluff_txs.reserve(arg.txs.size());
     }
     else
-    {
-      tx_relay = relay_method::stem;
       stem_txs.reserve(arg.txs.size());
-    }
 
     for (auto& tx : arg.txs)
     {
@@ -962,6 +971,7 @@ namespace cryptonote
           fluff_txs.push_back(std::move(tx));
           break;
         default:
+        case relay_method::forward: // not supposed to happen here
         case relay_method::none:
           break;
       }
diff --git a/src/cryptonote_protocol/enums.h b/src/cryptonote_protocol/enums.h
index a3a52b83f..36e8ca04c 100644
--- a/src/cryptonote_protocol/enums.h
+++ b/src/cryptonote_protocol/enums.h
@@ -37,6 +37,7 @@ namespace cryptonote
   {
     none = 0, //!< Received via RPC with `do_not_relay` set
     local,    //!< Received via RPC; trying to send over i2p/tor, etc.
+    forward,  //!< Received over i2p/tor; timer delayed before ipv4/6 public broadcast
     stem,     //!< Received/send over network using Dandelion++ stem
     fluff,    //!< Received/sent over network using Dandelion++ fluff
     block     //!< Received in block, takes precedence over others
diff --git a/src/cryptonote_protocol/levin_notify.cpp b/src/cryptonote_protocol/levin_notify.cpp
index 127801092..0ff194986 100644
--- a/src/cryptonote_protocol/levin_notify.cpp
+++ b/src/cryptonote_protocol/levin_notify.cpp
@@ -357,11 +357,15 @@ namespace levin
           return true;
         });
 
-        // Always send txs in stem mode over i2p/tor, see comments in `send_txs` below.
+        /* Always send with `fluff` flag, even over i2p/tor. The hidden service
+	   will disable the forwarding delay and immediately fluff. The i2p/tor
+	   network is therefore replacing the sybil protection of Dandelion++.
+	   Dandelion++ stem phase over i2p/tor is also worth investigating
+	   (with/without "noise"?). */
         for (auto& connection : connections)
         {
           std::sort(connection.first.begin(), connection.first.end()); // don't leak receive order
-          make_payload_send_txs(*zone_->p2p, std::move(connection.first), connection.second, zone_->pad_txs, zone_->is_public);
+          make_payload_send_txs(*zone_->p2p, std::move(connection.first), connection.second, zone_->pad_txs, true);
         }
 
         if (next_flush != std::chrono::steady_clock::time_point::max())
@@ -811,12 +815,11 @@ namespace levin
         case relay_method::block:
           return false;
         case relay_method::stem:
-	  tx_relay = relay_method::fluff; // don't set stempool embargo when skipping to fluff
-	  /* fallthrough */
+        case relay_method::forward:
         case relay_method::local:
           if (zone_->is_public)
           {
-	    // this will change a local tx to stem or fluff ...
+            // this will change a local/forward tx to stem or fluff ...
             zone_->strand.dispatch(
               dandelionpp_notify{zone_, std::addressof(core), std::move(txs), source}
             );
@@ -824,6 +827,11 @@ namespace levin
           }
           /* fallthrough */
         case relay_method::fluff:
+          /* If sending stem/forward/local txes over non public networks,
+             continue to claim that relay mode even though it used the "fluff"
+             routine. A "fluff" over i2p/tor is not the same as a "fluff" over
+             ipv4/6. Marking it as "fluff" here will make the tx immediately
+             visible externally from this node, which is not desired. */
           core.on_transactions_relayed(epee::to_span(txs), tx_relay);
           zone_->strand.dispatch(fluff_notify{zone_, std::move(txs), source});
           break;