Simplify variants of compute_note_hash_and_nullif #11638
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nventuro
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Feb 21, 2025
This removes the `addNote` function from PXE (`addNullifiedNote` had been removed in #11822). With this change, PXE no longer needs to understand how to compute note hashes and perform nonce discovery, which means we can also get rid of all of that code, _plus_ we can delete the mandatory `compute_note_hash_and_optionally_a_nullifier` contract function, _plus_ all of the auxiliary code used to call those. Instead, contracts that wish to deliver notes to their recipients via offchain mechanisms (i.e. not the protocol logs) must create custom unconstrained functions that know how to construct said notes and add them to PXE. For cases such as `TransparentNote`, where all of the note contents are public already, this is quite simple: `aztec::discovery::process_private_log` can be leveraged to a great degree by mimicking the log encoding aztec-nr uses - see the TokenBlacklist and Test contracts for examples of this. More fine grained control could be achieved by calling `aztec::discovery::attempt_note_nonce_discovery` and then the `deliver_note` oracle (which is essentially what `process_private_log` does, sans the decoding). The removal of `compute_note_hash_and_optionally_a_nullifier` freed us from some legacy burdens in having to produce the 4 field array, dealing with optional nullifier computation, etc., which in turn allowed for the contract library method `_compute_note_hash_and_optionally_a_nullifier` to be streamlined and converted into the new `compute_note_hash_and_nullifier`, which matches `aztec::discovery::ComputeNoteHashAndNullifier` and hence results in much easier use of the discovery functions. Tagging @critesjosh since `addNote` was quite a basic and old primitive. Closes #11638.
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Now that we are performing nonce discovery inside aztec-nr we have multiple places in which we need to invoke this function. Ideally we'd simply remove the top-level unconstrained
compute_note_hash_and_nulliffn, have the macros inject a contract library method with thenote::discovery::ComputeNoteHashAndNullifiersignature and just use that everywhere. We could also delete the utility innotes/utils.nrsince it just adds more calls back and forth, resulting in making it hard to follow what's going on.This would also be a good opportunity to make sure we're not trusting the contract to perform correct siloing of note hashes and instead do it ourselves in PXE.
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