Add merkle_crh_sprout() and tidy note* things

zebra-chain/src/sapling/tree.rs

@@ -25,21 +25,19 @@ use super::commitment::pedersen_hashes::pedersen_hash;
 
 /// MerkleCRH^Sapling Hash Function
 ///
-/// MerkleCRH^Sapling(layer, left, right) := PedersenHash(“Zcash_PH”, l || left ||right)
+/// MerkleCRH^Sapling(layer, left, right) := PedersenHash(“Zcash_PH”, l || left || right)
 /// where l = I2LEBSP_6(MerkleDepth^Sapling − 1 − layer)
 ///
 /// https://zips.z.cash/protocol/protocol.pdf#merklecrh
-// TODO: refine layer as a wrapper type around a bitvec/bitslice?
-// TODO: refine output type as *NodeHash, combine with RootHash
-fn merkle_crh_sapling(layer: u8, left: [u8; 32], right: [u8; 32]) -> jubjub::Fq {
+fn merkle_crh_sapling(layer: u8, left: [u8; 32], right: [u8; 32]) -> [u8; 32] {
     let mut s: BitVec<Lsb0, u8> = BitVec::new();
 
     // Prefix: l = I2LEBSP_6(MerkleDepth^Sapling − 1 − layer)
     s.append(&mut bitvec![31 - layer; 1]);
     s.append(&mut BitVec::<Lsb0, u8>::from_slice(&left[..]));
     s.append(&mut BitVec::<Lsb0, u8>::from_slice(&right[..]));
 
-    pedersen_hash(*b"Zcash_PH", &s)
+    pedersen_hash(*b"Zcash_PH", &s).to_bytes()
 }
 
 /// The index of a note’s commitment at the leafmost layer of its Note
@@ -54,7 +52,7 @@ pub struct Position(pub(crate) u64);
 /// Sapling Note Commitment Tree
 #[derive(Clone, Debug, Default, Eq, PartialEq)]
 #[cfg_attr(test, derive(Arbitrary))]
-struct SaplingNoteCommitmentTree;
+struct NoteCommitmentTree;
 
 /// Sapling note commitment tree root node hash.
 ///
@@ -72,8 +70,8 @@ impl fmt::Debug for Root {
     }
 }
 
-impl From<SaplingNoteCommitmentTree> for Root {
-    fn from(_tree: SaplingNoteCommitmentTree) -> Self {
+impl From<NoteCommitmentTree> for Root {
+    fn from(_tree: NoteCommitmentTree) -> Self {
         // TODO: The Sapling note commitment tree requires a Pedersen
         // hash function, not SHA256.
 
@@ -87,21 +85,21 @@ impl From<SaplingNoteCommitmentTree> for Root {
     }
 }
 
-impl SaplingNoteCommitmentTree {
+impl NoteCommitmentTree {
     /// Get the Jubjub-based Pedersen hash of root node of this merkle
     /// tree of commitment notes.
     pub fn hash(&self) -> [u8; 32] {
         unimplemented!();
     }
 }
 
-impl ZcashSerialize for SaplingNoteCommitmentTree {
+impl ZcashSerialize for NoteCommitmentTree {
     fn zcash_serialize<W: io::Write>(&self, _writer: W) -> Result<(), io::Error> {
         unimplemented!();
     }
 }
 
-impl ZcashDeserialize for SaplingNoteCommitmentTree {
+impl ZcashDeserialize for NoteCommitmentTree {
     fn zcash_deserialize<R: io::Read>(_reader: R) -> Result<Self, SerializationError> {
         unimplemented!();
     }

zebra-chain/src/sprout/tree.rs

@@ -10,11 +10,36 @@
 //!
 //! A root of a note commitment tree is associated with each treestate.
 #![allow(clippy::unit_arg)]
+#![allow(dead_code)]
 
 use std::fmt;
 
+use byteorder::{ByteOrder, LittleEndian};
 #[cfg(test)]
 use proptest_derive::Arbitrary;
+use sha2::digest::generic_array::{typenum::U64, GenericArray};
+
+/// MerkleCRH^Sprout Hash Function
+///
+/// MerkleCRH^Sprout(layer, left, right) := SHA256Compress(left || right)
+///
+/// `layer` is unused for Sprout but used for the Sapling equivalent.
+///
+/// https://zips.z.cash/protocol/protocol.pdf#merklecrh
+fn merkle_crh_sprout(left: [u8; 32], right: [u8; 32]) -> [u8; 32] {
+    let mut state = [0u32; 8];
+    let mut block = GenericArray::<u8, U64>::default();
+
+    block.as_mut_slice()[0..32].copy_from_slice(&left[..]);
+    block.as_mut_slice()[32..63].copy_from_slice(&right[..]);
+
+    sha2::compress256(&mut state, &[block]);
+
+    let mut derived_bytes = [0u8; 32];
+    LittleEndian::write_u32_into(&state, &mut derived_bytes);
+
+    derived_bytes
+}
 
 /// Sprout note commitment tree root node hash.
 ///