refactor: cleaning up messaging types (#5442)

Fixes #5420

noir-projects/aztec-nr/aztec/src/hash.nr

@@ -1,15 +1,53 @@
 use dep::protocol_types::{
-    address::AztecAddress, 
-    constants::GENERATOR_INDEX__L1_TO_L2_MESSAGE_SECRET, 
-    hash::{pedersen_hash, silo_nullifier}};
+    address::{AztecAddress, EthAddress},
+    constants::{GENERATOR_INDEX__L1_TO_L2_MESSAGE_SECRET, GENERATOR_INDEX__NULLIFIER},
+    hash::{pedersen_hash, silo_nullifier}
+};
 
-use dep::protocol_types::hash::{hash_args, hash_args_array};
+use dep::protocol_types::hash::{hash_args, hash_args_array, sha256_to_field};
 
 pub fn compute_secret_hash(secret: Field) -> Field {
     // TODO(#1205) This is probably not the right index to use
     pedersen_hash([secret], GENERATOR_INDEX__L1_TO_L2_MESSAGE_SECRET)
 }
 
+pub fn compute_message_hash(
+    sender: EthAddress,
+    chain_id: Field,
+    recipient: AztecAddress,
+    version: Field,
+    content: Field,
+    secret_hash: Field
+) -> Field {
+    let mut hash_bytes = [0 as u8; 192];
+    let sender_bytes = sender.to_field().to_be_bytes(32);
+    let chain_id_bytes = chain_id.to_be_bytes(32);
+    let recipient_bytes = recipient.to_field().to_be_bytes(32);
+    let version_bytes = version.to_be_bytes(32);
+    let content_bytes = content.to_be_bytes(32);
+    let secret_hash_bytes = secret_hash.to_be_bytes(32);
+
+    for i in 0..32 {
+        hash_bytes[i] = sender_bytes[i];
+        hash_bytes[i + 32] = chain_id_bytes[i];
+        hash_bytes[i + 64] = recipient_bytes[i];
+        hash_bytes[i + 96] = version_bytes[i];
+        hash_bytes[i + 128] = content_bytes[i];
+        hash_bytes[i + 160] = secret_hash_bytes[i];
+    }
+
+    sha256_to_field(hash_bytes)
+}
+
+// The nullifier of a l1 to l2 message is the hash of the message salted with the secret and index of the message hash
+// in the L1 to L2 message tree
+pub fn compute_message_nullifier(message_hash: Field, secret: Field, leaf_index: Field) -> Field {
+    pedersen_hash(
+        [message_hash, secret, leaf_index],
+        GENERATOR_INDEX__NULLIFIER
+    )
+}
+
 pub fn compute_siloed_nullifier(address: AztecAddress, nullifier: Field) -> Field {
     silo_nullifier(address, nullifier)
-}
+}

noir-projects/aztec-nr/aztec/src/messaging.nr

@@ -1,9 +1,9 @@
-mod l1_to_l2_message;
-
-use crate::oracle::get_l1_to_l2_membership_witness::get_l1_to_l2_membership_witness;
+use crate::{
+    hash::{compute_secret_hash, compute_message_hash, compute_message_nullifier},
+    oracle::get_l1_to_l2_membership_witness::get_l1_to_l2_membership_witness
+};
 
 use dep::std::merkle::compute_merkle_root;
-use crate::messaging::l1_to_l2_message::L1ToL2Message;
 use dep::protocol_types::{constants::L1_TO_L2_MSG_TREE_HEIGHT, address::{AztecAddress, EthAddress}, utils::arr_copy_slice};
 
 pub fn process_l1_to_l2_message(
@@ -15,15 +15,8 @@ pub fn process_l1_to_l2_message(
     content: Field,
     secret: Field
 ) -> Field {
-    let mut msg = L1ToL2Message::new(
-        portal_contract_address,
-        chain_id,
-        storage_contract_address,
-        version,
-        content,
-        secret
-    );
-    let message_hash = msg.hash();
+    let secret_hash = compute_secret_hash(secret);
+    let message_hash = compute_message_hash(portal_contract_address, chain_id, storage_contract_address, version, content, secret_hash);
 
     let returned_message = get_l1_to_l2_membership_witness(storage_contract_address, message_hash, secret);
     let leaf_index = returned_message[0];
@@ -34,12 +27,5 @@ pub fn process_l1_to_l2_message(
     let root = compute_merkle_root(message_hash, leaf_index, sibling_path);
     assert(root == l1_to_l2_root, "Message not in state");
 
-    // Note: Had to add this line to make it work (wasted an hour debugging this). L1ToL2Message noir struct is
-    // an abomination and it would not have ever got to that state if people followed the logical rule of 
-    // "deserialize(serialize(object)) == object" always being true (there are a few params which are not
-    // serialzied). Will refactor that in a separate PR.
-    // TODO(#5420)
-    msg.tree_index = leaf_index;
-
-    msg.compute_nullifier()
+    compute_message_nullifier(message_hash, secret, leaf_index)
 }