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Remove redundant checks during note encryption #394

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merged 1 commit into from
May 26, 2023
Merged

Remove redundant checks during note encryption #394

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26 changes: 7 additions & 19 deletions src/note_encryption.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,6 @@ use crate::{
OutgoingViewingKey, PreparedEphemeralPublicKey, PreparedIncomingViewingKey, SharedSecret,
},
note::{ExtractedNoteCommitment, Nullifier, RandomSeed},
spec::diversify_hash,
value::{NoteValue, ValueCommitment},
Address, Note,
};
Expand Down Expand Up @@ -52,10 +51,10 @@ pub(crate) fn prf_ock_orchard(
fn orchard_parse_note_plaintext_without_memo<F>(
domain: &OrchardDomain,
plaintext: &[u8],
get_validated_pk_d: F,
get_pk_d: F,
) -> Option<(Note, Address)>
where
F: FnOnce(&Diversifier) -> Option<DiversifiedTransmissionKey>,
F: FnOnce(&Diversifier) -> DiversifiedTransmissionKey,
{
assert!(plaintext.len() >= COMPACT_NOTE_SIZE);

Expand All @@ -72,7 +71,7 @@ where
&domain.rho,
))?;

let pk_d = get_validated_pk_d(&diversifier)?;
let pk_d = get_pk_d(&diversifier);

let recipient = Address::from_parts(diversifier, pk_d);
let note = Option::from(Note::from_parts(recipient, value, domain.rho, rseed))?;
Expand Down Expand Up @@ -209,29 +208,18 @@ impl Domain for OrchardDomain {
plaintext: &[u8],
) -> Option<(Self::Note, Self::Recipient)> {
orchard_parse_note_plaintext_without_memo(self, plaintext, |diversifier| {
Some(DiversifiedTransmissionKey::derive(ivk, diversifier))
DiversifiedTransmissionKey::derive(ivk, diversifier)
})
}

fn parse_note_plaintext_without_memo_ovk(
&self,
pk_d: &Self::DiversifiedTransmissionKey,
esk: &Self::EphemeralSecretKey,
ephemeral_key: &EphemeralKeyBytes,
_esk: &Self::EphemeralSecretKey,
_ephemeral_key: &EphemeralKeyBytes,
Comment on lines +218 to +219
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@daira daira May 19, 2023 •
edited
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Suggested change
_esk: &Self::EphemeralSecretKey,
_ephemeral_key: &EphemeralKeyBytes,

See https://github.com/zcash/librustzcash/pull/848/files#r1199198303

It may seem as though this is making life more difficult because removing these arguments is a breaking change, but strictly speaking the change to the guarantee of the method is a breaking API change anyway, even if not one that would otherwise be detected by the Rust compiler.

That is, it would be incorrect to mix a version of orchard from after this PR with a version of zcash_note_encryption from before zcash/librustzcash#848 — not (as it happens) because it would be insecure per se, but because that usage hasn't been reviewed.

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Mixing in the way you describe cannot happen, because the traits would not be version-compatible. Rust code is never dynamically linked internally.

plaintext: &NotePlaintextBytes,
) -> Option<(Self::Note, Self::Recipient)> {
orchard_parse_note_plaintext_without_memo(self, &plaintext.0, |diversifier| {
if esk
.derive_public(diversify_hash(diversifier.as_array()))
.to_bytes()
.0
== ephemeral_key.0
{
Some(*pk_d)
} else {
None
}
})
orchard_parse_note_plaintext_without_memo(self, &plaintext.0, |_| *pk_d)
}

fn extract_memo(&self, plaintext: &NotePlaintextBytes) -> Self::Memo {
Expand Down