82 lines
2.6 KiB
Rust
82 lines
2.6 KiB
Rust
#![allow(clippy::unit_arg)]
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#![allow(dead_code)]
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use group::GroupEncoding;
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use halo2::pasta::pallas;
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use super::super::{
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commitment::NoteCommitment, keys::NullifierDerivingKey, sinsemilla::*, tree::Position,
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};
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/// Orchard ixing Pedersen hash Function
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///
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/// Used to compute ρ from a note commitment and its position in the note
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/// commitment tree. It takes as input a Pedersen commitment P, and hashes it
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/// with another input x.
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///
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/// MixingPedersenHash(P, x) := P + [x]GroupHash^P^(r)(“Zcash_P_”, “”)
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///
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/// https://zips.z.cash/protocol/protocol.pdf#concretemixinghash
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// TODO: I'M EXTRAPOLATING HERE, DOUBLE CHECK THE SPEC WHEN FINALIZED
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#[allow(non_snake_case)]
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pub fn mixing_pedersen_hash(P: pallas::Point, x: pallas::Scalar) -> pallas::Point {
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P + pallas_group_hash(b"Zcash_P_", b"") * x
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}
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/// A cryptographic permutation, defined in [poseidonhash].
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///
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/// PoseidonHash(x, y) = f([x, y, 0])_1 (using 1-based indexing).
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///
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/// [poseidonhash]: https://zips.z.cash/protocol/nu5.pdf#poseidonhash
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fn poseidon_hash(x: pallas::Base, y: pallas::Base) -> pallas::Base {
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unimplemented!()
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}
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/// Derive the nullifier for a Orchard note.
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///
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/// Instantiated using the PoseidonHash hash function defined in [§5.4.1.10
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/// ‘PoseidonHash Function’][poseidon]
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///
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/// PRF^nfOrchard(nk*, ρ*) := PoseidonHash(nk*, ρ*)
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///
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/// [concreteprfs]: https://zips.z.cash/protocol/protocol.pdf#concreteprfs
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/// [poseidonhash]: https://zips.z.cash/protocol/nu5.pdf#poseidonhash
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fn prf_nf(nk: [u8; 32], rho: [u8; 32]) -> [u8; 32] {
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poseidon_hash(nk.into(), rho.into()).into()
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}
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/// A Nullifier for Orchard transactions
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#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize, Hash)]
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#[cfg_attr(
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any(test, feature = "proptest-impl"),
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derive(proptest_derive::Arbitrary)
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)]
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pub struct Nullifier(pub [u8; 32]);
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impl From<[u8; 32]> for Nullifier {
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fn from(buf: [u8; 32]) -> Self {
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Self(buf)
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}
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}
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impl<'a> From<(NoteCommitment, Position, &'a NullifierDerivingKey)> for Nullifier {
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/// Derive a `Nullifier` for an Orchard _note_.
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///
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/// For a _note_, the _nullifier_ is derived as PRF^nfOrchard_nk(ρ*), where
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/// k is a representation of the _nullifier deriving key_ associated with
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/// the _note_ and ρ = repr_P(ρ).
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///
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/// https://zips.z.cash/protocol/nu5.pdf#commitmentsandnullifiers
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fn from((cm, pos, nk): (NoteCommitment, Position, &'a NullifierDerivingKey)) -> Self {
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let rho = pallas::Affine::from(mixing_pedersen_hash(cm.0.into(), pos.0.into()));
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Nullifier(prf_nf(nk.into(), rho.to_bytes()))
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}
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}
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impl From<Nullifier> for [u8; 32] {
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fn from(n: Nullifier) -> Self {
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n.0
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}
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}
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