refactor: minor naming cleanup (#7144)

noir-projects/noir-protocol-circuits/crates/private-kernel-lib/src/components/kernel_circuit_output_hints.nr

@@ -44,10 +44,12 @@ unconstrained pub fn generate_hints(previous_kernel: PrivateKernelCircuitPublicI
     let sorted_note_hash_hints = sort_get_order_hints_asc(previous_kernel.end.new_note_hashes);
 
     let mut siloed_note_hashes = [0; MAX_NEW_NOTE_HASHES_PER_TX];
-    let first_nullifier = previous_kernel.end.new_nullifiers[0].value();
+
+    // First nullifier is tx hash.
+    let tx_hash = previous_kernel.end.new_nullifiers[0].value();
     let unsiloed_note_hashes = previous_kernel.end.new_note_hashes;
     for i in 0..unsiloed_note_hashes.len() {
-        siloed_note_hashes[i] = silo_note_hash(unsiloed_note_hashes[i], first_nullifier, i);
+        siloed_note_hashes[i] = silo_note_hash(unsiloed_note_hashes[i], tx_hash, i);
     }
 
     // nullifiers

noir-projects/noir-protocol-circuits/crates/private-kernel-lib/src/components/kernel_circuit_output_validator.nr

@@ -70,11 +70,11 @@ impl KernelCircuitOutputValidator {
     }
 
     fn validate_propagated_sorted_siloed_values(self, hints: Hints) {
-        // new_note_hashes
-        let first_nullifier = self.output.end.new_nullifiers[0];
+        // First nullifier is tx hash.
+        let tx_hash = self.output.end.new_nullifiers[0];
         let unsiloed_note_hashes = self.previous_kernel.end.new_note_hashes;
         for i in 0..unsiloed_note_hashes.len() {
-            let siloed_note_hash = silo_note_hash(unsiloed_note_hashes[i], first_nullifier, i);
+            let siloed_note_hash = silo_note_hash(unsiloed_note_hashes[i], tx_hash, i);
             assert_eq(hints.siloed_note_hashes[i], siloed_note_hash, "mismatch siloed note hashes");
         }
 

noir-projects/noir-protocol-circuits/crates/private-kernel-lib/src/components/kernel_circuit_public_inputs_composer.nr

@@ -129,15 +129,14 @@ impl KernelCircuitPublicInputsComposer {
     }
 
     fn silo_note_hashes(&mut self) {
-        let first_nullifier = self.public_inputs.end.new_nullifiers.get_unchecked(0).value();
-        // This check is unnecessary. The 0th nullifier will always be set a non-zero value in private_kernel_init.
-        // assert(first_nullifier != 0, "The 0th nullifier in the accumulated nullifier array is zero");
+        // First nullifier is tx hash.
+        let tx_hash = self.public_inputs.end.new_nullifiers.get_unchecked(0).value();
 
         let note_hashes = self.public_inputs.end.new_note_hashes.storage;
         for i in 0..note_hashes.len() {
             self.public_inputs.end.new_note_hashes.storage[i].note_hash.value = silo_note_hash(
                 note_hashes[i],
-                first_nullifier,
+                tx_hash,
                 i
             );
         }

noir-projects/noir-protocol-circuits/crates/private-kernel-lib/src/private_kernel_tail.nr

@@ -123,10 +123,11 @@ mod tests {
         // A helper function that uses the first nullifer in the previous kernel to compute the unique siloed
         // note_hashes for the given note_hashes.
         pub fn compute_output_note_hashes<N>(self, note_hashes: [ScopedNoteHash; N]) -> [Field; N] {
-            let first_nullifier = self.previous_kernel.new_nullifiers.get_unchecked(0).value();
+            // First nullifier is tx hash.
+            let tx_hash = self.previous_kernel.new_nullifiers.get_unchecked(0).value();
             let mut output = [0; N];
             for i in 0..N {
-                output[i] = silo_note_hash(note_hashes[i], first_nullifier, i);
+                output[i] = silo_note_hash(note_hashes[i], tx_hash, i);
             }
             output
         }

noir-projects/noir-protocol-circuits/crates/private-kernel-lib/src/private_kernel_tail_to_public.nr

@@ -109,11 +109,12 @@ mod tests {
         // A helper function that uses the first nullifer in the previous kernel to compute the unique siloed
         // note_hashes for the given note_hashes.
         pub fn compute_output_note_hashes<N>(self, note_hashes: [ScopedNoteHash; N]) -> [NoteHash; N] {
-            let first_nullifier = self.previous_kernel.new_nullifiers.get_unchecked(0).value();
+            // First nullifier is tx hash.
+            let tx_hash = self.previous_kernel.new_nullifiers.get_unchecked(0).value();
             let mut output = [NoteHash::empty(); N];
             for i in 0..N {
                 output[i] = NoteHash {
-                    value: silo_note_hash(note_hashes[i], first_nullifier, i),
+                    value: silo_note_hash(note_hashes[i], tx_hash, i),
                     counter: 0, // Counter is cleared so it's not exposed to the public.
                 };
             }

noir-projects/noir-protocol-circuits/crates/types/src/hash.nr

@@ -10,10 +10,9 @@ use crate::{
     GENERATOR_INDEX__VK, GENERATOR_INDEX__NOTE_HASH_NONCE, GENERATOR_INDEX__UNIQUE_NOTE_HASH,
     MAX_ENCRYPTED_LOGS_PER_TX, MAX_NOTE_ENCRYPTED_LOGS_PER_TX
 },
-    contract_class_id::ContractClassId, merkle_tree::root::root_from_sibling_path,
-    messaging::l2_to_l1_message::{L2ToL1Message, ScopedL2ToL1Message},
-    recursion::verification_key::VerificationKey, traits::{Hash, is_empty},
-    utils::{uint256::U256, field::field_from_bytes_32_trunc}
+    merkle_tree::root::root_from_sibling_path, messaging::l2_to_l1_message::ScopedL2ToL1Message,
+    recursion::verification_key::VerificationKey, traits::is_empty,
+    utils::field::field_from_bytes_32_trunc
 };
 use dep::std::hash::{pedersen_hash_with_separator, sha256};
 
@@ -35,11 +34,12 @@ pub fn private_functions_root_from_siblings(
     root_from_sibling_path(function_leaf, function_leaf_index, function_leaf_sibling_path)
 }
 
-pub fn compute_note_hash_nonce(first_nullifier: Field, note_hash_index: u32) -> Field {
+fn compute_note_hash_nonce(tx_hash: Field, note_index_in_tx: u32) -> Field {
+    // Hashing tx hash with note index in tx is guaranteed to be unique
     pedersen_hash(
         [
-        first_nullifier,
-        note_hash_index as Field
+        tx_hash,
+        note_index_in_tx as Field
     ],
         GENERATOR_INDEX__NOTE_HASH_NONCE
     )
@@ -60,11 +60,11 @@ pub fn compute_siloed_note_hash(app: AztecAddress, unique_note_hash: Field) -> F
     )
 }
 
-pub fn silo_note_hash(note_hash: ScopedNoteHash, first_nullifier: Field, index: u32) -> Field {
+pub fn silo_note_hash(note_hash: ScopedNoteHash, tx_hash: Field, note_index_in_tx: u32) -> Field {
     if note_hash.contract_address.is_zero() {
         0
     } else {
-        let nonce = compute_note_hash_nonce(first_nullifier, index);
+        let nonce = compute_note_hash_nonce(tx_hash, note_index_in_tx);
         let unique_note_hash = compute_unique_note_hash(nonce, note_hash.value());
         compute_siloed_note_hash(note_hash.contract_address, unique_note_hash)
     }

noir-projects/noir-protocol-circuits/crates/types/src/tests/fixture_builder.nr

@@ -430,10 +430,11 @@ impl FixtureBuilder {
     }
 
     pub fn add_siloed_note_hash(&mut self, value: Field) {
-        let first_nullifier = self.new_nullifiers.get(0).value();
+        // First nullifier is tx hash.
+        let tx_hash = self.new_nullifiers.get(0).value();
         let index = self.new_note_hashes.len();
         let note_hash = NoteHash { value, counter: 0 }.scope(0, self.storage_contract_address);
-        let siloed_value = silo_note_hash(note_hash, first_nullifier, index);
+        let siloed_value = silo_note_hash(note_hash, tx_hash, index);
         self.add_new_note_hash(siloed_value, 0);
     }