refactor: small internal event fn cleanup (#19151)

This just deletes a function that was unused and moves some docs around.

Author: nventuro

noir-projects/aztec-nr/aztec/src/messages/logs/event.nr

@@ -1,40 +1,16 @@
 use crate::{
     event::event_interface::EventInterface,
     messages::{
-        encoding::{encode_message, MESSAGE_CIPHERTEXT_LEN, MESSAGE_EXPANDED_METADATA_LEN},
-        encryption::{aes128::AES128, message_encryption::MessageEncryption},
+        encoding::{encode_message, MESSAGE_EXPANDED_METADATA_LEN},
         msg_type::PRIVATE_EVENT_MSG_TYPE_ID,
     },
-    oracle::random::random,
 };
-use protocol_types::{address::AztecAddress, traits::{Serialize, ToField}};
+use protocol_types::traits::{Serialize, ToField};
 
 global PRIVATE_EVENT_RESERVED_FIELDS: u32 = 1;
 global PRIVATE_EVENT_RANDOMNESS_INDEX: u32 = 0;
 
-/// Creates an encrypted private event message (i.e. one of type `PRIVATE_EVENT_MSG_TYPE_ID`) by encoding the contents
-/// of the event and then encrypting them for `recipient`.
-pub fn to_encrypted_private_event_message<Event>(
-    event: Event,
-    recipient: AztecAddress,
-) -> ([Field; MESSAGE_CIPHERTEXT_LEN], Field)
-where
-    Event: EventInterface + Serialize,
-{
-    // In private events, we automatically inject randomness to prevent event commitment preimage attacks and event
-    // commitment collisions (the commitments are included in the nullifier tree and duplicate nullifiers are by
-    // definition not allowed).
-    // Safety: We use the randomness to preserve the privacy of the event recipient by preventing brute-forcing,
-    // so a malicious sender could use non-random values to make the event less private. But they already know
-    // the full event pre-image anyway, and so the recipient already trusts them to not disclose this information.
-    // We can therefore assume that the sender will cooperate in the random value generation.
-    let randomness = unsafe { random() };
-
-    let plaintext = private_event_to_message_plaintext(event, randomness);
-
-    (AES128::encrypt(plaintext, recipient), randomness)
-}
-
+/// Creates the plaintext for a private event message (i.e. one of type [PRIVATE_EVENT_MSG_TYPE_ID]).
 pub fn private_event_to_message_plaintext<Event>(
     event: Event,
     randomness: Field,

noir-projects/aztec-nr/aztec/src/messages/logs/note.nr

@@ -40,6 +40,7 @@ where
     prefix_with_tag(message_ciphertext, recipient)
 }
 
+/// Creates the plaintext for a private note message (i.e. one of type [PRIVATE_NOTE_MSG_TYPE_ID]).
 pub fn private_note_to_message_plaintext<Note>(
     note: Note,
     owner: AztecAddress,
@@ -63,6 +64,7 @@ where
     encode_message(PRIVATE_NOTE_MSG_TYPE_ID, Note::get_id() as u64, msg_content)
 }
 
+/// Creates the plaintext for a partial note private message (i.e. one of type [PARTIAL_NOTE_PRIVATE_MSG_TYPE_ID]).
 pub fn partial_note_private_content_to_message_plaintext<PartialNotePrivateContent>(
     partial_note_private_content: PartialNotePrivateContent,
     owner: AztecAddress,

noir-projects/aztec-nr/aztec/src/messages/msg_type.nr

@@ -1,3 +1,16 @@
+/// A message containing the information about a private note, i.e. one that has been created fully privately with no
+/// public fields.
+///
+/// This message contains all information necessary in order to prove existence of the note.
 pub global PRIVATE_NOTE_MSG_TYPE_ID: u64 = 0;
+
+/// A message containing the private informatio of a partial note, i.e. one that has both private and public fields.
+///
+/// This message contains all information necessary in order to find the public note information once it is created, and
+/// then prove existence of the note.
 pub global PARTIAL_NOTE_PRIVATE_MSG_TYPE_ID: u64 = 1;
+
+/// A message containing the information about a private event, i.e. one that has been emitted privately.
+///
+/// This message contains all information necessary in order to prove existence of the event.
 pub global PRIVATE_EVENT_MSG_TYPE_ID: u64 = 2;