Sanitize outbound address responses.

This aims to prevent a remote peer from inspecting timings of all messages
received by this node.

Cargo.lock

@@ -1539,6 +1539,7 @@ dependencies = [
  "gumdrop 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "hyper 0.13.0-alpha.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.7.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "tokio 0.2.0-alpha.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "toml 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",

zebra-network/src/constants.rs

@@ -25,6 +25,12 @@ pub const LIVE_PEER_DURATION: Duration = Duration::from_secs(60 + 10 + 10 + 10);
 /// connected peer.
 pub const HEARTBEAT_INTERVAL: Duration = Duration::from_secs(60);
 
+/// Truncate timestamps in outbound address messages to this time interval.
+///
+/// This is intended to prevent a peer from learning exactly when we recieved
+/// messages from each of our peers.
+pub const TIMESTAMP_TRUNCATION_SECONDS: i64 = 30 * 60;
+
 /// The User-Agent string provided by the node.
 pub const USER_AGENT: &'static str = "🦓Zebra v2.0.0-alpha.0🦓";
 

zebra-network/src/meta_addr.rs

@@ -31,6 +31,16 @@ pub struct MetaAddr {
     pub last_seen: DateTime<Utc>,
 }
 
+impl MetaAddr {
+    /// Sanitize this `MetaAddr` before sending it to a remote peer.
+    pub fn sanitize(mut self) -> MetaAddr {
+        let interval = crate::constants::TIMESTAMP_TRUNCATION_SECONDS;
+        let ts = self.last_seen.timestamp();
+        self.last_seen = Utc.timestamp(ts - ts.rem_euclid(interval), 0);
+        self
+    }
+}
+
 impl Ord for MetaAddr {
     /// `MetaAddr`s are sorted newest-first, and then in an arbitrary
     /// but determinate total order.
@@ -78,3 +88,23 @@ impl ZcashDeserialize for MetaAddr {
         })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    // XXX remove this test and replace it with a proptest instance.
+    #[test]
+    fn sanitize_truncates_timestamps() {
+        let entry = MetaAddr {
+            services: PeerServices::default(),
+            addr: "127.0.0.1:8233".parse().unwrap(),
+            last_seen: Utc.timestamp(1573680222, 0),
+        }
+        .sanitize();
+        // We want the sanitized timestamp to be a multiple of the truncation interval.
+        assert_eq!(
+            entry.last_seen.timestamp() % crate::constants::TIMESTAMP_TRUNCATION_SECONDS,
+            0
+        );
+    }
+}

zebrad/Cargo.toml

@@ -6,6 +6,7 @@ version = "0.1.0"
 edition = "2018"
 
 [dependencies]
+rand = "0.7"
 chrono = "0.4"
 abscissa_core = "0.3.0"
 failure = "0.1"

zebrad/src/commands/seed.rs

@@ -10,6 +10,8 @@ use std::{
 use abscissa_core::{config, Command, FrameworkError, Options, Runnable};
 use futures::channel::oneshot;
 use tower::{buffer::Buffer, Service, ServiceExt};
+use tracing::{span, Level};
+
 use zebra_network::{AddressBook, BoxedStdError, Request, Response};
 
 use crate::{config::ZebradConfig, prelude::*};
@@ -61,7 +63,8 @@ impl Service<Request> for SeedService {
     }
 
     fn call(&mut self, req: Request) -> Self::Future {
-        info!("SeedService handling a request: {:?}", req);
+        let span = span!(Level::DEBUG, "SeedService::call", req = ?req);
+        let _guard = span.enter();
 
         let address_book = if let SeederState::Ready(address_book) = &self.state {
             address_book
@@ -71,16 +74,28 @@ impl Service<Request> for SeedService {
 
         let response = match req {
             Request::GetPeers => {
-                debug!(address_book.len = address_book.lock().unwrap().len());
-                info!("SeedService responding to GetPeers");
-                Ok::<Response, Self::Error>(Response::Peers(
-                    address_book.lock().unwrap().peers().collect(),
-                ))
+                // Collect a list of known peers from the address book
+                // and sanitize their timestamps.
+                let mut peers = address_book
+                    .lock()
+                    .unwrap()
+                    .peers()
+                    .map(|addr| addr.sanitize())
+                    .collect::<Vec<_>>();
+                // The peers are still ordered by recency, so shuffle them.
+                use rand::seq::SliceRandom;
+                peers.shuffle(&mut rand::thread_rng());
+                // Finally, truncate the list so that we do not trivially
+                // reveal our entire peer set.
+                peers.truncate(50);
+                debug!(peers.len = peers.len(), peers = ?peers);
+                Ok(Response::Peers(peers))
+            }
+            _ => {
+                debug!("ignoring request");
+                Ok::<Response, Self::Error>(Response::Ok)
             }
-            _ => Ok::<Response, Self::Error>(Response::Ok),
         };
-
-        info!("SeedService response: {:?}", response);
         return Box::pin(futures::future::ready(response));
     }
 }