fix: SubscriptionNote preimage attack (#8390)

noir-projects/noir-contracts/contracts/app_subscription_contract/src/subscription_note.nr

@@ -1,21 +1,22 @@
-use dep::aztec::prelude::{AztecAddress, PrivateContext, NoteHeader, NoteInterface};
 use dep::aztec::{
-    protocol_types::{constants::GENERATOR_INDEX__NOTE_NULLIFIER, hash::poseidon2_hash_with_separator},
-    note::utils::compute_note_hash_for_nullify, keys::getters::get_nsk_app
+    hash::poseidon2_hash_with_separator, note::utils::compute_note_hash_for_nullify,
+    keys::getters::get_nsk_app, oracle::unsafe_rand::unsafe_rand,
+    prelude::{PrivateContext, NoteHeader, NoteInterface},
+    protocol_types::constants::GENERATOR_INDEX__NOTE_NULLIFIER
 };
 
-global SUBSCRIPTION_NOTE_LEN: Field = 3;
-// ADDRESS_NOTE_LEN * 32 + 32(storage_slot as bytes) + 32(note_type_id as bytes)
-global SUBSCRIPTION_NOTE_BYTES_LEN: Field = 3 * 32 + 64;
+global SUBSCRIPTION_NOTE_LEN: Field = 4;
+// SUBSCRIPTION_NOTE_BYTES_LEN * 32 + 32(storage_slot as bytes) + 32(note_type_id as bytes)
+global SUBSCRIPTION_NOTE_BYTES_LEN: Field = SUBSCRIPTION_NOTE_LEN * 32 + 64;
 
-// Stores a public key composed of two fields
-// TODO: Do we need to include a nonce, in case we want to read/nullify/recreate with the same pubkey value?
 #[aztec(note)]
 struct SubscriptionNote {
     // The nullifying public key hash is used with the nsk_app to ensure that the note can be privately spent.
     npk_m_hash: Field,
     expiry_block_number: Field,
     remaining_txs: Field,
+    // Randomness of the note to hide its contents
+    randomness: Field,
 }
 
 impl NoteInterface<SUBSCRIPTION_NOTE_LEN, SUBSCRIPTION_NOTE_BYTES_LEN> for SubscriptionNote {
@@ -43,6 +44,9 @@ impl NoteInterface<SUBSCRIPTION_NOTE_LEN, SUBSCRIPTION_NOTE_BYTES_LEN> for Subsc
 
 impl SubscriptionNote {
     pub fn new(npk_m_hash: Field, expiry_block_number: Field, remaining_txs: Field) -> Self {
-        SubscriptionNote { npk_m_hash, expiry_block_number, remaining_txs, header: NoteHeader::empty() }
+        let randomness = unsafe {
+            unsafe_rand()
+        };
+        Self { npk_m_hash, expiry_block_number, remaining_txs, randomness, header: NoteHeader::empty() }
     }
 }