reencode gossipsub messages with anonymization (#378)

This helps protect against clients sending more data than they should
and thus getting penalized on topics that require anonymity

libp2p/protocols/pubsub/pubsub.nim

@@ -83,7 +83,7 @@ proc send*(p: PubSub, peer: PubSubPeer, msg: RPCMsg) =
   ##
 
   trace "sending pubsub message to peer", peer, msg = shortLog(msg)
-  peer.send(msg)
+  peer.send(msg, p.anonymize)
 
 proc broadcast*(
   p: PubSub,

libp2p/protocols/pubsub/pubsubpeer.nim

@@ -193,7 +193,7 @@ proc sendImpl(conn: Connection, encoded: seq[byte]) {.async.} =
 
     await conn.close() # This will clean up the send connection
 
-proc send*(p: PubSubPeer, msg: RPCMsg) =
+proc send*(p: PubSubPeer, msg: RPCMsg, anonymize: bool) =
   doAssert(not isNil(p), "pubsubpeer nil!")
 
   let conn = p.sendConn
@@ -203,15 +203,20 @@ proc send*(p: PubSubPeer, msg: RPCMsg) =
 
   trace "sending msg to peer", peer = p, rpcMsg = shortLog(msg)
 
+  # When sending messages, we take care to re-encode them with the right
+  # anonymization flag to ensure that we're not penalized for sending invalid
+  # or malicious data on the wire - in particular, re-encoding protects against
+  # some forms of valid but redundantly encoded protobufs with unknown or
+  # duplicated fields
   let encoded = if p.hasObservers():
     # trigger send hooks
     var mm = msg # hooks can modify the message
     p.sendObservers(mm)
-    encodeRpcMsg(mm)
+    encodeRpcMsg(mm, anonymize)
   else:
     # If there are no send hooks, we redundantly re-encode the message to
     # protobuf for every peer - this could easily be improved!
-    encodeRpcMsg(msg)
+    encodeRpcMsg(msg, anonymize)
 
   if encoded.len <= 0:
     debug "empty message, skipping", p, msg

libp2p/protocols/pubsub/rpc/message.nim

@@ -31,7 +31,7 @@ func defaultMsgIdProvider*(m: Message): string =
   byteutils.toHex(m.seqno) & $m.fromPeer
 
 proc sign*(msg: Message, privateKey: PrivateKey): CryptoResult[seq[byte]] =
-  ok((? privateKey.sign(PubSubPrefix & encodeMessage(msg))).getBytes())
+  ok((? privateKey.sign(PubSubPrefix & encodeMessage(msg, false))).getBytes())
 
 proc verify*(m: Message): bool =
   if m.signature.len > 0 and m.key.len > 0:
@@ -43,7 +43,7 @@ proc verify*(m: Message): bool =
     var key: PublicKey
     if remote.init(m.signature) and key.init(m.key):
       trace "verifying signature", remoteSignature = remote
-      result = remote.verify(PubSubPrefix & encodeMessage(msg), key)
+      result = remote.verify(PubSubPrefix & encodeMessage(msg, false), key)
 
   if result:
     libp2p_pubsub_sig_verify_success.inc()
@@ -60,7 +60,7 @@ proc init*(
   var msg = Message(data: data, topicIDs: @[topic])
 
   # order matters, we want to include seqno in the signature
-  if seqno.isSome: 
+  if seqno.isSome:
     msg.seqno = @(seqno.get().toBytesBE())
 
   if peer.isSome:

libp2p/protocols/pubsub/rpc/protobuf.nim

@@ -78,24 +78,24 @@ proc write*(pb: var ProtoBuffer, field: int, subs: SubOpts) =
   ipb.finish()
   pb.write(field, ipb)
 
-proc encodeMessage*(msg: Message): seq[byte] =
+proc encodeMessage*(msg: Message, anonymize: bool): seq[byte] =
   var pb = initProtoBuffer()
-  if len(msg.fromPeer) > 0:
+  if len(msg.fromPeer) > 0 and not anonymize:
     pb.write(1, msg.fromPeer)
   pb.write(2, msg.data)
-  if len(msg.seqno) > 0:
+  if len(msg.seqno) > 0 and not anonymize:
     pb.write(3, msg.seqno)
   for topic in msg.topicIDs:
     pb.write(4, topic)
-  if len(msg.signature) > 0:
+  if len(msg.signature) > 0 and not anonymize:
     pb.write(5, msg.signature)
-  if len(msg.key) > 0:
+  if len(msg.key) > 0 and not anonymize:
     pb.write(6, msg.key)
   pb.finish()
   pb.buffer
 
-proc write*(pb: var ProtoBuffer, field: int, msg: Message) =
-  pb.write(field, encodeMessage(msg))
+proc write*(pb: var ProtoBuffer, field: int, msg: Message, anonymize: bool) =
+  pb.write(field, encodeMessage(msg, anonymize))
 
 proc decodeGraft*(pb: ProtoBuffer): ProtoResult[ControlGraft] {.
      inline.} =
@@ -242,13 +242,13 @@ proc decodeMessages*(pb: ProtoBuffer): ProtoResult[seq[Message]] {.inline.} =
     trace "decodeMessages: no messages found"
   ok(msgs)
 
-proc encodeRpcMsg*(msg: RPCMsg): seq[byte] =
+proc encodeRpcMsg*(msg: RPCMsg, anonymize: bool): seq[byte] =
   trace "encodeRpcMsg: encoding message", msg = msg.shortLog()
   var pb = initProtoBuffer()
   for item in msg.subscriptions:
     pb.write(1, item)
   for item in msg.messages:
-    pb.write(2, item)
+    pb.write(2, item, anonymize)
   if msg.control.isSome():
     pb.write(3, msg.control.get())
   if len(pb.buffer) > 0: