Merge pull request #4787

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

2 files changed, 33 insertions, 0 deletions

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);
   }
   //------------------------------------------------------------------------------------------------------------------------