Merge pull request #4787

3dba7f25 protocol: option to pad transaction relay to the next kB (moneromooo-monero)

4 files changed, 50 insertions, 1 deletions

diff --git a/src/cryptonote_core/cryptonote_core.cpp b/src/cryptonote_core/cryptonote_core.cpp
index f918afa33..2f55cc40b 100644
--- a/src/cryptonote_core/cryptonote_core.cpp
+++ b/src/cryptonote_core/cryptonote_core.cpp
@@ -160,6 +160,11 @@ namespace cryptonote
   , "Relay blocks as normal blocks"
   , false
   };
+  static const command_line::arg_descriptor<bool> arg_pad_transactions  = {
+    "pad-transactions"
+  , "Pad relayed transactions to help defend against traffic volume analysis"
+  , false
+  };
   static const command_line::arg_descriptor<size_t> arg_max_txpool_weight  = {
     "max-txpool-weight"
   , "Set maximum txpool weight in bytes."
@@ -185,7 +190,8 @@ namespace cryptonote
               m_disable_dns_checkpoints(false),
               m_update_download(0),
               m_nettype(UNDEFINED),
-              m_update_available(false)
+              m_update_available(false),
+              m_pad_transactions(false)
   {
     m_checkpoints_updating.clear();
     set_cryptonote_protocol(pprotocol);
@@ -279,6 +285,7 @@ namespace cryptonote
     command_line::add_arg(desc, arg_offline);
     command_line::add_arg(desc, arg_disable_dns_checkpoints);
     command_line::add_arg(desc, arg_max_txpool_weight);
+    command_line::add_arg(desc, arg_pad_transactions);
     command_line::add_arg(desc, arg_block_notify);
 
     miner::init_options(desc);
@@ -317,6 +324,7 @@ namespace cryptonote
     set_enforce_dns_checkpoints(command_line::get_arg(vm, arg_dns_checkpoints));
     test_drop_download_height(command_line::get_arg(vm, arg_test_drop_download_height));
     m_fluffy_blocks_enabled = !get_arg(vm, arg_no_fluffy_blocks);
+    m_pad_transactions = get_arg(vm, arg_pad_transactions);
     m_offline = get_arg(vm, arg_offline);
     m_disable_dns_checkpoints = get_arg(vm, arg_disable_dns_checkpoints);
     if (!command_line::is_arg_defaulted(vm, arg_fluffy_blocks))
diff --git a/src/cryptonote_core/cryptonote_core.h b/src/cryptonote_core/cryptonote_core.h
index 0ae063342..cc53fce58 100644
--- a/src/cryptonote_core/cryptonote_core.h
+++ b/src/cryptonote_core/cryptonote_core.h
@@ -755,6 +755,13 @@ namespace cryptonote
      bool fluffy_blocks_enabled() const { return m_fluffy_blocks_enabled; }
 
      /**
+      * @brief get whether transaction relay should be padded
+      *
+      * @return whether transaction relay should be padded
+      */
+     bool pad_transactions() const { return m_pad_transactions; }
+
+     /**
       * @brief check a set of hashes against the precompiled hash set
       *
       * @return number of usable blocks
@@ -1013,6 +1020,7 @@ namespace cryptonote
 
      bool m_fluffy_blocks_enabled;
      bool m_offline;
+     bool m_pad_transactions;
    };
 }
 
diff --git a/src/cryptonote_protocol/cryptonote_protocol_defs.h b/src/cryptonote_protocol/cryptonote_protocol_defs.h
index db159f0f4..d5bb50930 100644
--- a/src/cryptonote_protocol/cryptonote_protocol_defs.h
+++ b/src/cryptonote_protocol/cryptonote_protocol_defs.h
@@ -146,9 +146,11 @@ namespace cryptonote
     struct request
     {
       std::vector<blobdata>   txs;
+      std::string _; // padding
 
       BEGIN_KV_SERIALIZE_MAP()
         KV_SERIALIZE(txs)
+        KV_SERIALIZE(_)
       END_KV_SERIALIZE_MAP()
     };
   };
diff --git a/src/cryptonote_protocol/cryptonote_protocol_handler.inl b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
index 5ba637c2f..1de0cde07 100644
--- a/src/cryptonote_protocol/cryptonote_protocol_handler.inl
+++ b/src/cryptonote_protocol/cryptonote_protocol_handler.inl
@@ -1726,8 +1726,39 @@ skip:
   bool t_cryptonote_protocol_handler<t_core>::relay_transactions(NOTIFY_NEW_TRANSACTIONS::request& arg, cryptonote_connection_context& exclude_context)
   {
     // no check for success, so tell core they're relayed unconditionally
+    const bool pad_transactions = m_core.pad_transactions();
+    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
+    }
+
     return relay_post_notify<NOTIFY_NEW_TRANSACTIONS>(arg, exclude_context);
   }
   //------------------------------------------------------------------------------------------------------------------------