Merge #13298: Net: Bucketing INV delays (1 bucket) for incoming connections to hide tx time

d45b344ffd Bucket for inbound when scheduling invs to hide tx time (Gleb)

Pull request description:

  It has been brought up to my attention that current random delays mechanism (originally intended to obfuscate transaction metadata) allows to easily estimate the time a transaction was received by a node.

  It may be done by connecting multiple observer nodes to the same node. Each of those nodes will generate its own schedule of delays. Combined metadata regarding those events from different sources allows an observer to estimate transaction time.

  After this patch a spy won't gain additional information by just creating multiple connections to a target.

Tree-SHA512: c71dae5ff350b614cb40a8e201fd0562d3e03e3e72a5099718cd451f0d84c66d5e52bbaf0d5b4b75137514c8efdedcc6ef4df90142b360153f04ad0721545ab1

1 files changed, 14 insertions, 2 deletions

diff --git a/src/net.cpp b/src/net.cpp
index d806059ece..e44aa1fdb4 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2864,8 +2864,20 @@ bool CConnman::ForNode(NodeId id, std::function<bool(CNode* pnode)> func)
     return found != nullptr && NodeFullyConnected(found) && func(found);
 }
 
-int64_t PoissonNextSend(int64_t nNow, int average_interval_seconds) {
-    return nNow + (int64_t)(log1p(GetRand(1ULL << 48) * -0.0000000000000035527136788 /* -1/2^48 */) * average_interval_seconds * -1000000.0 + 0.5);
+int64_t CConnman::PoissonNextSendInbound(int64_t now, int average_interval_seconds)
+{
+    if (m_next_send_inv_to_incoming < now) {
+        // If this function were called from multiple threads simultaneously
+        // it would possible that both update the next send variable, and return a different result to their caller.
+        // This is not possible in practice as only the net processing thread invokes this function.
+        m_next_send_inv_to_incoming = PoissonNextSend(now, average_interval_seconds);
+    }
+    return m_next_send_inv_to_incoming;
+}
+
+int64_t PoissonNextSend(int64_t now, int average_interval_seconds)
+{
+    return now + (int64_t)(log1p(GetRand(1ULL << 48) * -0.0000000000000035527136788 /* -1/2^48 */) * average_interval_seconds * -1000000.0 + 0.5);
 }
 
 CSipHasher CConnman::GetDeterministicRandomizer(uint64_t id) const