fix(gossipsub): signed messages use monotonically increasing seq numbers

protocols/gossipsub/CHANGELOG.md

@@ -1,3 +1,10 @@
+# 0.44.2 - unreleased
+
+- Signed messages now use sequential integers in the sequence number field.
+  See [PR 3551].
+
+[PR 3551]: https://github.com/libp2p/rust-libp2p/pull/3551
+
 # 0.44.1
 
 - Migrate from `prost` to `quick-protobuf`. This removes `protoc` dependency. See [PR 3312].

protocols/gossipsub/src/behaviour.rs

@@ -80,7 +80,7 @@ mod tests;
 #[derive(Clone)]
 pub enum MessageAuthenticity {
     /// Message signing is enabled. The author will be the owner of the key and the sequence number
-    /// will be a random number.
+    /// will be linearly increasing.
     Signed(Keypair),
     /// Message signing is disabled.
     ///
@@ -155,6 +155,8 @@ enum PublishConfig {
         keypair: Keypair,
         author: PeerId,
         inline_key: Option<Vec<u8>>,
+        last_seq_no: u64, // This starts from a random number and increases then overflows (if
+                          // required)
     },
     Author(PeerId),
     RandomAuthor,
@@ -190,6 +192,7 @@ impl From<MessageAuthenticity> for PublishConfig {
                     keypair,
                     author: public_key.to_peer_id(),
                     inline_key: key,
+                    last_seq_no: rand::random(),
                 }
             }
             MessageAuthenticity::Author(peer_id) => PublishConfig::Author(peer_id),
@@ -2749,18 +2752,21 @@ where
 
     /// Constructs a [`RawMessage`] performing message signing if required.
     pub(crate) fn build_raw_message(
-        &self,
+        &mut self,
         topic: TopicHash,
         data: Vec<u8>,
     ) -> Result<RawMessage, PublishError> {
-        match &self.publish_config {
+        match &mut self.publish_config {
             PublishConfig::Signing {
                 ref keypair,
                 author,
                 inline_key,
+                mut last_seq_no,
             } => {
-                // Build and sign the message
-                let sequence_number: u64 = rand::random();
+                // Increment the last sequence number
+                last_seq_no = last_seq_no.wrapping_add(1);
+
+                let sequence_number = last_seq_no;
 
                 let signature = {
                     let message = proto::Message {

protocols/gossipsub/src/lib.rs

@@ -50,8 +50,9 @@
 //! - **Sequence Numbers** - A message on the gossipsub network is identified by the source
 //! [`libp2p_core::PeerId`] and a nonce (sequence number) of the message. The sequence numbers in
 //! this implementation are sent as raw bytes across the wire. They are 64-bit big-endian unsigned
-//! integers. They are chosen at random in this implementation of gossipsub, but are sequential in
-//! the current go implementation.
+//! integers. When messages are signed, they are monotonically increasing integers starting from a
+//! random value and wrapping around u64::MAX. When messages are unsigned, they are chosen at random.
+//! NOTE: These numbers are sequential in the current go implementation.
 //!
 //! # Peer Discovery
 //!

protocols/gossipsub/src/protocol.rs

@@ -573,7 +573,7 @@ mod tests {
 
             // generate an arbitrary GossipsubMessage using the behaviour signing functionality
             let config = Config::default();
-            let gs: Behaviour =
+            let mut gs: Behaviour =
                 Behaviour::new(crate::MessageAuthenticity::Signed(keypair.0), config).unwrap();
             let data = (0..g.gen_range(10..10024u32))
                 .map(|_| u8::arbitrary(g))