add nullifier types (#568)

* add nullifier types

* Apply suggestions from code review

Co-authored-by: Deirdre Connolly <deirdre@zfnd.org>

* add zcash_deserialize impls

* Add docs

Co-authored-by: Deirdre Connolly <deirdre@zfnd.org>

zebra-chain/src/lib.rs

@@ -17,6 +17,7 @@ pub mod equihash_solution;
 pub mod keys;
 pub mod note_commitment_tree;
 pub mod notes;
+pub mod nullifier;
 pub mod proofs;
 pub mod serialization;
 pub mod transaction;

zebra-chain/src/nullifier.rs

@@ -0,0 +1,4 @@
+//! Nullifier set types for sproud and sapling
+
+pub mod sapling;
+pub mod sprout;

zebra-chain/src/nullifier/sapling.rs

@@ -0,0 +1,30 @@
+//! Sapling Nullifier Set types and impls
+#![allow(clippy::unit_arg)]
+use crate::serialization::{ReadZcashExt, SerializationError, ZcashDeserialize, ZcashSerialize};
+use serde::{Deserialize, Serialize};
+use std::io;
+
+/// A Nullifier Set for Sapling transactions
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(test, derive(proptest_derive::Arbitrary))]
+pub struct Nullifier([u8; 32]);
+
+impl From<[u8; 32]> for Nullifier {
+    fn from(buf: [u8; 32]) -> Self {
+        Self(buf)
+    }
+}
+
+impl ZcashDeserialize for Nullifier {
+    fn zcash_deserialize<R: io::Read>(mut reader: R) -> Result<Self, SerializationError> {
+        let bytes = reader.read_32_bytes()?;
+
+        Ok(Self(bytes))
+    }
+}
+
+impl ZcashSerialize for Nullifier {
+    fn zcash_serialize<W: io::Write>(&self, mut writer: W) -> Result<(), io::Error> {
+        writer.write_all(&self.0[..])
+    }
+}

zebra-chain/src/nullifier/sprout.rs

@@ -0,0 +1,30 @@
+//! Sprout Nullifier Set types and impls
+#![allow(clippy::unit_arg)]
+use crate::serialization::{ReadZcashExt, SerializationError, ZcashDeserialize, ZcashSerialize};
+use serde::{Deserialize, Serialize};
+use std::io;
+
+/// A Nullifier Set for Sprout transactions
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(test, derive(proptest_derive::Arbitrary))]
+pub struct Nullifier([u8; 32]);
+
+impl From<[u8; 32]> for Nullifier {
+    fn from(buf: [u8; 32]) -> Self {
+        Self(buf)
+    }
+}
+
+impl ZcashDeserialize for Nullifier {
+    fn zcash_deserialize<R: io::Read>(mut reader: R) -> Result<Self, SerializationError> {
+        let bytes = reader.read_32_bytes()?;
+
+        Ok(Self(bytes))
+    }
+}
+
+impl ZcashSerialize for Nullifier {
+    fn zcash_serialize<W: io::Write>(&self, mut writer: W) -> Result<(), io::Error> {
+        writer.write_all(&self.0[..])
+    }
+}

zebra-chain/src/transaction/joinsplit.rs

@@ -23,7 +23,7 @@ pub struct JoinSplit<P: ZkSnarkProof> {
     /// A nullifier for the input notes.
     ///
     /// XXX refine type to [T; 2] -- there are two nullifiers
-    pub nullifiers: [[u8; 32]; 2],
+    pub nullifiers: [crate::nullifier::sprout::Nullifier; 2],
     /// A note commitment for this output note.
     ///
     /// XXX refine type to [T; 2] -- there are two commitments

zebra-chain/src/transaction/serialize.rs

@@ -236,8 +236,8 @@ impl<P: ZkSnarkProof> ZcashSerialize for JoinSplit<P> {
         writer.write_u64::<LittleEndian>(self.vpub_old.into())?;
         writer.write_u64::<LittleEndian>(self.vpub_new.into())?;
         writer.write_all(&self.anchor[..])?;
-        writer.write_all(&self.nullifiers[0][..])?;
-        writer.write_all(&self.nullifiers[1][..])?;
+        self.nullifiers[0].zcash_serialize(&mut writer)?;
+        self.nullifiers[1].zcash_serialize(&mut writer)?;
         writer.write_all(&self.commitments[0][..])?;
         writer.write_all(&self.commitments[1][..])?;
         writer.write_all(&self.ephemeral_key.as_bytes()[..])?;
@@ -257,7 +257,10 @@ impl<P: ZkSnarkProof> ZcashDeserialize for JoinSplit<P> {
             vpub_old: reader.read_u64::<LittleEndian>()?.try_into()?,
             vpub_new: reader.read_u64::<LittleEndian>()?.try_into()?,
             anchor: reader.read_32_bytes()?,
-            nullifiers: [reader.read_32_bytes()?, reader.read_32_bytes()?],
+            nullifiers: [
+                crate::nullifier::sprout::Nullifier::zcash_deserialize(&mut reader)?,
+                crate::nullifier::sprout::Nullifier::zcash_deserialize(&mut reader)?,
+            ],
             commitments: [reader.read_32_bytes()?, reader.read_32_bytes()?],
             ephemeral_key: x25519_dalek::PublicKey::from(reader.read_32_bytes()?),
             random_seed: reader.read_32_bytes()?,
@@ -314,7 +317,7 @@ impl ZcashSerialize for Spend {
     fn zcash_serialize<W: io::Write>(&self, mut writer: W) -> Result<(), io::Error> {
         writer.write_all(&self.cv[..])?;
         writer.write_all(&self.anchor.0[..])?;
-        writer.write_all(&self.nullifier[..])?;
+        self.nullifier.zcash_serialize(&mut writer)?;
         writer.write_all(&<[u8; 32]>::from(self.rk)[..])?;
         self.zkproof.zcash_serialize(&mut writer)?;
         writer.write_all(&<[u8; 64]>::from(self.spend_auth_sig)[..])?;
@@ -328,7 +331,7 @@ impl ZcashDeserialize for Spend {
         Ok(Spend {
             cv: reader.read_32_bytes()?,
             anchor: SaplingNoteTreeRootHash(reader.read_32_bytes()?),
-            nullifier: reader.read_32_bytes()?,
+            nullifier: crate::nullifier::sapling::Nullifier::zcash_deserialize(&mut reader)?,
             rk: reader.read_32_bytes()?.into(),
             zkproof: Groth16Proof::zcash_deserialize(&mut reader)?,
             spend_auth_sig: reader.read_64_bytes()?.into(),

zebra-chain/src/transaction/shielded_data.rs

@@ -18,9 +18,7 @@ pub struct Spend {
     /// A root of the Sapling note commitment tree at some block height in the past.
     pub anchor: SaplingNoteTreeRootHash,
     /// The nullifier of the input note.
-    ///
-    /// XXX refine to a specific type.
-    pub nullifier: [u8; 32],
+    pub nullifier: crate::nullifier::sapling::Nullifier,
     /// The randomized public key for `spend_auth_sig`.
     pub rk: redjubjub::PublicKeyBytes<SpendAuth>,
     /// The ZK spend proof.

zebra-chain/src/transaction/tests/arbitrary.rs

@@ -22,7 +22,7 @@ impl<P: ZkSnarkProof + Arbitrary + 'static> Arbitrary for JoinSplit<P> {
             any::<Amount<NonNegative>>(),
             any::<Amount<NonNegative>>(),
             array::uniform32(any::<u8>()),
-            array::uniform2(array::uniform32(any::<u8>())),
+            array::uniform2(any::<crate::nullifier::sprout::Nullifier>()),
             array::uniform2(array::uniform32(any::<u8>())),
             array::uniform32(any::<u8>()),
             array::uniform32(any::<u8>()),
@@ -155,7 +155,7 @@ impl Arbitrary for Spend {
         (
             array::uniform32(any::<u8>()),
             any::<SaplingNoteTreeRootHash>(),
-            array::uniform32(any::<u8>()),
+            any::<crate::nullifier::sapling::Nullifier>(),
             array::uniform32(any::<u8>()),
             any::<Groth16Proof>(),
             vec(any::<u8>(), 64),