Flesh out Orchard note and nullifier derivation

zebra-chain/src/lib.rs

@@ -7,8 +7,6 @@
 #![doc(html_logo_url = "https://www.zfnd.org/images/zebra-icon.png")]
 #![doc(html_root_url = "https://doc.zebra.zfnd.org/zebra_chain")]
 #![allow(clippy::try_err)]
-// Use the old lint name to build without warnings on stable until 1.51 is stable
-#![allow(clippy::unknown_clippy_lints)]
 // The actual lints we want to disable
 #![allow(clippy::unnecessary_wraps)]
 // Disable some broken or unwanted clippy nightly lints

zebra-chain/src/orchard/commitment.rs

@@ -18,8 +18,8 @@ use crate::{
 };
 
 use super::{
-    keys::{Diversifier, TransmissionKey},
-    note::Note,
+    keys::{prf_expand, Diversifier, TransmissionKey},
+    note::{self, SeedRandomness},
     sinsemilla::*,
 };
 
@@ -36,10 +36,22 @@ where
     pallas::Scalar::from_bytes_wide(&bytes)
 }
 
-/// The randomness used in the Simsemilla Hash for note commitment.
+/// The randomness used in the Simsemilla hash for note commitment.
 #[derive(Copy, Clone, Debug, PartialEq)]
 pub struct CommitmentRandomness(pallas::Scalar);
 
+impl From<SeedRandomness> for CommitmentRandomness {
+    /// rcm = ToScalar^Orchard((PRF^expand_rseed ([5]))
+    ///
+    /// https://zips.z.cash/protocol/nu5.pdf#orchardsend
+    fn from(rseed: SeedRandomness) -> Self {
+        Self(pallas::Scalar::from_bytes_wide(&prf_expand(
+            rseed.0,
+            vec![&[5]],
+        )))
+    }
+}
+
 /// Note commitments for the output notes.
 #[derive(Clone, Copy, Deserialize, PartialEq, Serialize)]
 pub struct NoteCommitment(#[serde(with = "serde_helpers::Affine")] pub pallas::Affine);
@@ -106,7 +118,8 @@ impl NoteCommitment {
         diversifier: Diversifier,
         transmission_key: TransmissionKey,
         value: Amount<NonNegative>,
-        _note: Note,
+        rho: note::Rho,
+        psi: note::Psi,
     ) -> Option<(CommitmentRandomness, Self)>
     where
         T: RngCore + CryptoRng,
@@ -126,13 +139,17 @@ impl NoteCommitment {
             return None;
         }
 
-        let pk_d_bytes = <[u8; 32]>::from(transmission_key);
+        let pk_d_bytes: [u8; 32] = transmission_key.into();
         let v_bytes = value.to_bytes();
+        let rho_bytes: [u8; 32] = rho.into();
+        let psi_bytes: [u8; 32] = psi.into();
 
-        // g*d || pk*d || I2LEBSP64(v)
+        // g*d || pk*d || I2LEBSP_64(v) || I2LEBSP_l^Orchard_Base(ρ) || I2LEBSP_l^Orchard_base(ψ)
         s.append(&mut BitVec::<Lsb0, u8>::from_slice(&g_d_bytes[..]));
         s.append(&mut BitVec::<Lsb0, u8>::from_slice(&pk_d_bytes[..]));
         s.append(&mut BitVec::<Lsb0, u8>::from_slice(&v_bytes[..]));
+        s.append(&mut BitVec::<Lsb0, u8>::from_slice(&rho_bytes[..]));
+        s.append(&mut BitVec::<Lsb0, u8>::from_slice(&psi_bytes[..]));
 
         let rcm = CommitmentRandomness(generate_trapdoor(csprng));
 

zebra-chain/src/orchard/keys.rs

@@ -63,9 +63,9 @@ fn prp_d(K: [u8; 32], d: [u8; 11]) -> [u8; 11] {
 ///
 /// https://zips.z.cash/protocol/protocol.pdf#concreteprfs
 // TODO: This is basically a duplicate of the one in our sapling module, its
-// definition in the draft NU5 spec is incomplete so I'm putting it here in case
+// definition in the draft Nu5 spec is incomplete so I'm putting it here in case
 // it changes.
-fn prf_expand(sk: [u8; 32], t: Vec<&[u8]>) -> [u8; 64] {
+pub fn prf_expand(sk: [u8; 32], t: Vec<&[u8]>) -> [u8; 64] {
     let mut state = blake2b_simd::Params::new()
         .hash_length(64)
         .personal(b"Zcash_ExpandSeed")

zebra-chain/src/orchard/note.rs

@@ -3,7 +3,9 @@
 #![allow(clippy::unit_arg)]
 #![allow(dead_code)]
 
-use halo2::pasta::pallas;
+use group::GroupEncoding;
+use halo2::{arithmetic::FieldExt, pasta::pallas};
+use rand_core::{CryptoRng, RngCore};
 
 use crate::{
     amount::{Amount, NonNegative},
@@ -12,7 +14,8 @@ use crate::{
 
 use super::{
     commitment::CommitmentRandomness,
-    keys::{Diversifier, TransmissionKey},
+    keys::{prf_expand, Diversifier, TransmissionKey},
+    sinsemilla::extract_p,
 };
 
 #[cfg(any(test, feature = "proptest-impl"))]
@@ -23,6 +26,63 @@ mod nullifiers;
 pub use ciphertexts::{EncryptedNote, WrappedNoteKey};
 pub use nullifiers::Nullifier;
 
+#[derive(Clone, Debug)]
+pub struct SeedRandomness(pub(crate) [u8; 32]);
+
+/// Used as input to PRF^nf as part of deriving the _nullifier_ of the _note_.
+///
+/// When creating a new note from spending an old note, the new note's _rho_ is
+/// the _nullifier_ of the previous note. If creating a note from scratch (like
+/// a miner reward), a dummy note is constructed, and its nullifier as the _rho_
+/// for the actual output note. When creating a dummy note, its _rho_ is chosen
+/// as a random Pallas point's x-coordinate.
+///
+/// https://zips.z.cash/protocol/nu5.pdf#orcharddummynotes
+#[derive(Clone, Debug)]
+pub struct Rho(pub(crate) pallas::Base);
+
+impl From<Rho> for [u8; 32] {
+    fn from(rho: Rho) -> Self {
+        rho.0.to_bytes()
+    }
+}
+
+impl Rho {
+    pub fn new<T>(csprng: &mut T) -> Self
+    where
+        T: RngCore + CryptoRng,
+    {
+        let mut bytes = [0u8; 32];
+        csprng.fill_bytes(&mut bytes);
+
+        Self(extract_p(pallas::Point::from_bytes(&bytes).unwrap()))
+    }
+}
+
+/// Additional randomness used in deriving the _nullifier_.
+///
+/// https://zips.z.cash/protocol/nu5.pdf#orchardsend
+#[derive(Clone, Debug)]
+pub struct Psi(pub(crate) pallas::Base);
+
+impl From<Psi> for [u8; 32] {
+    fn from(psi: Psi) -> Self {
+        psi.0.to_bytes()
+    }
+}
+
+impl From<SeedRandomness> for Psi {
+    /// rcm = ToScalar^Orchard((PRF^expand_rseed ([9]))
+    ///
+    /// https://zips.z.cash/protocol/nu5.pdf#orchardsend
+    fn from(rseed: SeedRandomness) -> Self {
+        Self(pallas::Base::from_bytes_wide(&prf_expand(
+            rseed.0,
+            vec![&[9]],
+        )))
+    }
+}
+
 /// A Note represents that a value is spendable by the recipient who
 /// holds the spending key corresponding to a given shielded payment
 /// address.
@@ -36,9 +96,9 @@ pub struct Note {
     /// An integer representing the value of the _note_ in zatoshi.
     pub value: Amount<NonNegative>,
     /// Used as input to PRF^nf as part of deriving the _nullifier_ of the _note_.
-    pub rho: pallas::Base, // XXX: refine type?
+    pub rho: Rho,
     /// Additional randomness used in deriving the _nullifier_.
-    pub psi: pallas::Base, // XXX: refine type
+    pub psi: Psi,
     /// A random _commitment trapdoor_ used to produce the associated note
     /// commitment.
     pub rcm: CommitmentRandomness,

zebra-chain/src/orchard/note/nullifiers.rs

@@ -69,7 +69,8 @@ impl From<(NullifierDerivingKey, Note, NoteCommitment)> for Nullifier {
         //
         // [︀ (PRF^nfOrchard_nk(ρ) + ψ) mod q_P ]︀ K^Orchard + cm
         let scalar =
-            pallas::Scalar::from_bytes(&(prf_nf(nk.0, note.rho) + note.psi).to_bytes()).unwrap();
+            pallas::Scalar::from_bytes(&(prf_nf(nk.0, note.rho.0) + note.psi.0).to_bytes())
+                .unwrap();
 
         // Basically a new-gen Pedersen hash?
         Nullifier(extract_p((K * scalar) + cm.0))

zebra-chain/src/parameters/network_upgrade.rs

@@ -37,7 +37,7 @@ pub enum NetworkUpgrade {
     Heartwood,
     /// The Zcash protocol after the Canopy upgrade.
     Canopy,
-    /// The Zcash protocol after the NU5 upgrade.
+    /// The Zcash protocol after the Nu5 upgrade.
     ///
     /// Note: Network Upgrade 5 includes the Orchard Shielded Protocol, and
     /// other changes. The Nu5 code name has not been chosen yet.
@@ -56,7 +56,7 @@ pub(crate) const MAINNET_ACTIVATION_HEIGHTS: &[(block::Height, NetworkUpgrade)]
     (block::Height(653_600), Blossom),
     (block::Height(903_000), Heartwood),
     (block::Height(1_046_400), Canopy),
-    // TODO: Add NU5 mainnet activation height
+    // TODO: Add Nu5 mainnet activation height
 ];
 
 /// Testnet network upgrade activation heights.
@@ -71,7 +71,7 @@ pub(crate) const TESTNET_ACTIVATION_HEIGHTS: &[(block::Height, NetworkUpgrade)]
     (block::Height(584_000), Blossom),
     (block::Height(903_800), Heartwood),
     (block::Height(1_028_500), Canopy),
-    // TODO: Add NU5 testnet activation height
+    // TODO: Add Nu5 testnet activation height
 ];
 
 /// The Consensus Branch Id, used to bind transactions and blocks to a