Add ack signatures

Also modifies message signatures to be binding to from, not just from's key.

message-queue/src/main.rs

@@ -42,7 +42,9 @@ lazy_static::lazy_static! {
 fn queue_message(meta: Metadata, msg: Vec<u8>, sig: SchnorrSignature<Ristretto>) {
   {
     let from = (*KEYS).read().unwrap()[&meta.from];
-    assert!(sig.verify(from, message_challenge(from, meta.to, &meta.intent, &msg, sig.R)));
+    assert!(
+      sig.verify(from, message_challenge(meta.from, from, meta.to, &meta.intent, &msg, sig.R))
+    );
   }
 
   // Assert one, and only one of these, is the coordinator
@@ -85,8 +87,11 @@ fn get_next_message(service: Service, _expected: u64) -> Option<QueuedMessage> {
   Acknowledges a message as received and handled, meaning it'll no longer be returned as the next
   message.
 */
-fn ack_message(service: Service, id: u64, _signature: SchnorrSignature<Ristretto>) {
-  // TODO: Verify the signature
+fn ack_message(service: Service, id: u64, sig: SchnorrSignature<Ristretto>) {
+  {
+    let from = (*KEYS).read().unwrap()[&service];
+    assert!(sig.verify(from, ack_challenge(service, from, id, sig.R)));
+  }
 
   // Is it:
   // The acknowledged message should be > last acknowledged OR

message-queue/src/messages.rs

@@ -27,20 +27,39 @@ pub struct Metadata {
 }
 
 pub fn message_challenge(
-  from: <Ristretto as Ciphersuite>::G,
+  from: Service,
+  from_key: <Ristretto as Ciphersuite>::G,
   to: Service,
   intent: &[u8],
   msg: &[u8],
   nonce: <Ristretto as Ciphersuite>::G,
 ) -> <Ristretto as Ciphersuite>::F {
-  let mut transcript = RecommendedTranscript::new(b"Serai Message Queue v0.1");
+  let mut transcript = RecommendedTranscript::new(b"Serai Message Queue v0.1 Message");
   transcript.domain_separate(b"metadata");
-  transcript.append_message(b"from", from.to_bytes());
+  transcript.append_message(b"from", bincode::serialize(&from).unwrap());
+  transcript.append_message(b"from_key", from_key.to_bytes());
   transcript.append_message(b"to", bincode::serialize(&to).unwrap());
   transcript.append_message(b"intent", intent);
   transcript.domain_separate(b"message");
   transcript.append_message(b"msg", msg);
   transcript.domain_separate(b"signature");
   transcript.append_message(b"nonce", nonce.to_bytes());
-  <Ristretto as Ciphersuite>::hash_to_F(b"challenge", &transcript.challenge(b"challenge"))
+  <Ristretto as Ciphersuite>::hash_to_F(b"message_challenge", &transcript.challenge(b"challenge"))
+}
+
+pub fn ack_challenge(
+  from: Service,
+  from_key: <Ristretto as Ciphersuite>::G,
+  id: u64,
+  nonce: <Ristretto as Ciphersuite>::G,
+) -> <Ristretto as Ciphersuite>::F {
+  let mut transcript = RecommendedTranscript::new(b"Serai Message Queue v0.1 Ackowledgement");
+  transcript.domain_separate(b"metadata");
+  transcript.append_message(b"from", bincode::serialize(&from).unwrap());
+  transcript.append_message(b"from_key", from_key.to_bytes());
+  transcript.domain_separate(b"message");
+  transcript.append_message(b"id", id.to_le_bytes());
+  transcript.domain_separate(b"signature");
+  transcript.append_message(b"nonce", nonce.to_bytes());
+  <Ristretto as Ciphersuite>::hash_to_F(b"ack_challenge", &transcript.challenge(b"challenge"))
 }

message-queue/src/queue.rs

@@ -46,7 +46,8 @@ impl<D: Db> Queue<D> {
   }
 
   pub(crate) fn get_message(&self, id: u64) -> Option<QueuedMessage> {
-    let msg = self.0.get(self.message_key(id)).map(|bytes| serde_json::from_slice(&bytes).unwrap());
+    let msg: Option<QueuedMessage> =
+      self.0.get(self.message_key(id)).map(|bytes| serde_json::from_slice(&bytes).unwrap());
     if let Some(msg) = msg.as_ref() {
       assert_eq!(msg.id, id, "message stored at {id} has ID {}", msg.id);
     }

processor/src/coordinator.rs

@@ -15,7 +15,7 @@ use serde::{Serialize, Deserialize};
 use messages::{ProcessorMessage, CoordinatorMessage};
 
 use serai_client::primitives::NetworkId;
-use message_queue::{Service, Metadata, QueuedMessage, message_challenge};
+use message_queue::{Service, Metadata, QueuedMessage, message_challenge, ack_challenge};
 use reqwest::Client;
 
 #[derive(Clone, PartialEq, Eq, Debug)]
@@ -125,10 +125,8 @@ impl MessageQueue {
       let id = msg.id;
 
       // Deserialize it into a CoordinatorMessage
-      let msg: CoordinatorMessage = serde_json::from_str(
-        &String::from_utf8(msg.msg).expect("msg wasn't valid UTF-8 (not JSON?)"),
-      )
-      .expect("message wasn't a JSON-encoded CoordinatorMessage");
+      let msg: CoordinatorMessage =
+        serde_json::from_slice(&msg.msg).expect("message wasn't a JSON-encoded CoordinatorMessage");
       return Message { id, msg };
     }
   }
@@ -157,7 +155,14 @@ impl Coordinator for MessageQueue {
     let sig = SchnorrSignature::<Ristretto>::sign(
       &self.priv_key,
       nonce,
-      message_challenge(self.pub_key, metadata.to, &metadata.intent, msg.as_bytes(), nonce_pub),
+      message_challenge(
+        metadata.from,
+        self.pub_key,
+        metadata.to,
+        &metadata.intent,
+        msg.as_bytes(),
+        nonce_pub,
+      ),
     );
     self.queue(metadata, msg.into_bytes(), sig.serialize()).await;
   }
@@ -167,8 +172,16 @@ impl Coordinator for MessageQueue {
   }
 
   async fn ack(&mut self, msg: Message) {
-    // TODO: Use a proper signature once message-queue checks ack signatures
-    MessageQueue::ack(self, msg.id, vec![0; 64]).await
+    // TODO: Should this use OsRng? Deterministic or deterministic + random may be better.
+    let nonce = Zeroizing::new(<Ristretto as Ciphersuite>::F::random(&mut OsRng));
+    let nonce_pub = Ristretto::generator() * nonce.deref();
+    let sig = SchnorrSignature::<Ristretto>::sign(
+      &self.priv_key,
+      nonce,
+      ack_challenge(Service::Processor(self.network), self.pub_key, msg.id, nonce_pub),
+    );
+
+    MessageQueue::ack(self, msg.id, sig.serialize()).await
   }
 }