Move message_queue over to deduplication via intents

Due to each service having multiple distinct clocks, we can't expect a stable
ordering except the ordering an intact message-queue provides. The messages
emitted should be consistent however, solely with unknown order, which is why
we can craft intents based on their contents (already implemented by
processor-messages).

Cargo.lock

@@ -8689,6 +8689,7 @@ dependencies = [
 name = "serai-message-queue"
 version = "0.1.0"
 dependencies = [
+ "bincode",
  "ciphersuite",
  "flexible-transcript",
  "hex",

message-queue/Cargo.toml

@@ -20,6 +20,7 @@ serde = { version = "1", features = ["derive"] }
 
 # Encoders
 hex = "0.4"
+bincode = "1"
 serde_json = "1"
 
 # Cryptography

message-queue/src/main.rs

@@ -27,13 +27,13 @@ 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, &msg, sig.R)));
+    assert!(sig.verify(from, message_challenge(from, meta.to, &meta.intent, &msg, sig.R)));
   }
 
   // Assert one, and only one of these, is the coordinator
   assert!(matches!(meta.from, Service::Coordinator) ^ matches!(meta.to, Service::Coordinator));
 
-  // TODO: Verify the from_id hasn't been prior seen
+  // TODO: Verify the intent hasn't been prior seen
 
   // Queue it
   (*QUEUES).read().unwrap()[&meta.to].write().unwrap().queue_message(QueuedMessage {

message-queue/src/messages.rs

@@ -18,21 +18,26 @@ pub struct QueuedMessage {
   pub sig: Vec<u8>,
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug, Serialize, Deserialize)]
+#[derive(Clone, PartialEq, Eq, Debug, Serialize, Deserialize)]
 pub struct Metadata {
   pub from: Service,
   pub to: Service,
-  pub from_id: u64,
+  pub intent: Vec<u8>,
 }
 
 pub fn message_challenge(
   from: <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");
-  transcript.domain_separate(b"message");
+  transcript.domain_separate(b"metadata");
   transcript.append_message(b"from", from.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());