mirror of https://github.com/zcash/orchard.git
77 lines
2.6 KiB
Rust
77 lines
2.6 KiB
Rust
use group::Group;
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use halo2::arithmetic::CurveExt;
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use pasta_curves::{arithmetic::FieldExt, pallas};
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use rand::RngCore;
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use subtle::CtOption;
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use super::NoteCommitment;
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use crate::{
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keys::NullifierDerivingKey,
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spec::{extract_p, mod_r_p},
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};
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/// A unique nullifier for a note.
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#[derive(Debug, Clone)]
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pub struct Nullifier(pub(crate) pallas::Base);
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impl Nullifier {
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/// Generates a dummy nullifier for use as $\rho$ in dummy spent notes.
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///
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/// Nullifiers are required by consensus to be unique. For dummy output notes, we get
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/// this restriction as intended: the note's $\rho$ value is set to the nullifier of
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/// the accompanying spent note within the action, which is constrained by consensus
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/// to be unique. In the case of dummy spent notes, we get this restriction by
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/// following the chain backwards: the nullifier of the dummy spent note will be
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/// constrained by consensus to be unique, and the nullifier's uniqueness is derived
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/// from the uniqueness of $\rho$.
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///
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/// Instead of explicitly sampling for a unique nullifier, we rely here on the size of
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/// the base field to make the chance of sapling a colliding nullifier negligible.
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pub(crate) fn dummy(rng: &mut impl RngCore) -> Self {
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Nullifier(extract_p(&pallas::Point::random(rng)))
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}
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/// Deserialize the nullifier from a byte array.
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pub fn from_bytes(bytes: &[u8; 32]) -> CtOption<Self> {
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pallas::Base::from_bytes(bytes).map(Nullifier)
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}
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/// Serialize the nullifier to its canonical byte representation.
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pub fn to_bytes(&self) -> [u8; 32] {
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self.0.to_bytes()
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}
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/// $DeriveNullifier$.
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///
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/// Defined in [Zcash Protocol Spec § 4.16: Note Commitments and Nullifiers][commitmentsandnullifiers].
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///
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/// [commitmentsandnullifiers]: https://zips.z.cash/protocol/nu5.pdf#commitmentsandnullifiers
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pub(super) fn derive(
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nk: &NullifierDerivingKey,
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rho: pallas::Base,
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psi: pallas::Base,
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cm: NoteCommitment,
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) -> Self {
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let k = pallas::Point::hash_to_curve("z.cash:Orchard")(b"K");
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Nullifier(extract_p(&(k * mod_r_p(nk.prf_nf(rho) + psi) + cm.0)))
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}
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}
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/// Generators for property testing.
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#[cfg(any(test, feature = "test-dependencies"))]
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pub mod testing {
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use proptest::prelude::*;
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use pasta_curves::pallas;
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use super::Nullifier;
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prop_compose! {
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/// Generate a uniformly distributed nullifier value.
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pub fn arb_nullifier()(elems in prop::array::uniform4(prop::num::u64::ANY)) -> Nullifier {
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Nullifier(pallas::Base::from_raw(elems))
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}
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}
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}
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