Add legacy `CommitmentTree` and `IncrementalWitness` types.
These types were previously part of the `zcash_primitives` crate and are being included here to provide a migration path for when these types are removed from `zcash_primitives`.
This commit is contained in:
Kris Nuttycombe
parent
4e3c6a6378
commit
7cb2bdcc8f
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@ -11,7 +11,12 @@ and this project adheres to Rust's notion of
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- `incrementalmerkletree::frontier` Types that model the state at the rightmost
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node of a Merkle tree that is filled sequentially from the left. These have
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been migrated here from the `bridgetree` crate as they are useful outside
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of the context of the `bridgetree` data structures.
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of the context of the `bridgetree` data structures. Additional legacy types
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used for this modeling have been moved here from the `librustzcash` crate;
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these migrated types are available under a `legacy-api` feature flag.
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- `incrementalmerkletree::witness` Types migrated from `librustzcash` under
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the `legacy-api` feature flag related to constructing witnesses for leaves
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of a Merkle tree.
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## [0.3.1] - 2023-02-28
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@ -21,4 +21,5 @@ proptest = { version = "1.0.0", optional = true }
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proptest = "1.0.0"
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[features]
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legacy-api = []
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test-dependencies = ["proptest"]
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@ -3,6 +3,9 @@ use std::mem::size_of;
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use crate::{Address, Hashable, Level, Position, Source};
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#[cfg(feature = "legacy-api")]
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use {std::collections::VecDeque, std::iter::repeat};
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/// Validation errors that can occur during reconstruction of a Merkle frontier from
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/// its constituent parts.
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#[derive(Clone, Debug, PartialEq, Eq)]
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@ -244,9 +247,227 @@ impl<H: Hashable + Clone, const DEPTH: u8> Frontier<H, DEPTH> {
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}
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}
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#[cfg(feature = "legacy-api")]
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pub(crate) struct PathFiller<H> {
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pub(crate) queue: VecDeque<H>,
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}
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#[cfg(feature = "legacy-api")]
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impl<H: Hashable> PathFiller<H> {
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pub(crate) fn empty() -> Self {
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PathFiller {
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queue: VecDeque::new(),
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}
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}
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pub(crate) fn next(&mut self, level: Level) -> H {
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self.queue
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.pop_front()
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.unwrap_or_else(|| H::empty_root(level))
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}
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}
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/// A Merkle tree of note commitments.
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#[derive(Clone, Debug, PartialEq, Eq)]
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#[cfg(feature = "legacy-api")]
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pub struct CommitmentTree<H, const DEPTH: u8> {
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pub(crate) left: Option<H>,
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pub(crate) right: Option<H>,
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pub(crate) parents: Vec<Option<H>>,
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}
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#[cfg(feature = "legacy-api")]
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impl<H, const DEPTH: u8> CommitmentTree<H, DEPTH> {
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/// Creates an empty tree.
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pub fn empty() -> Self {
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CommitmentTree {
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left: None,
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right: None,
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parents: vec![],
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}
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}
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pub fn from_frontier(frontier: &Frontier<H, DEPTH>) -> Self
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where
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H: Clone,
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{
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frontier.value().map_or_else(Self::empty, |f| {
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let mut ommers_iter = f.ommers().iter().cloned();
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let (left, right) = if f.position().is_odd() {
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(
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ommers_iter
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.next()
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.expect("An ommer must exist if the frontier position is odd"),
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Some(f.leaf().clone()),
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)
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} else {
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(f.leaf().clone(), None)
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};
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let upos: usize = f.position().into();
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Self {
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left: Some(left),
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right,
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parents: (1u8..DEPTH)
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.into_iter()
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.map(|i| {
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if upos & (1 << i) == 0 {
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None
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} else {
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ommers_iter.next()
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}
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})
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.collect(),
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}
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})
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}
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pub fn to_frontier(&self) -> Frontier<H, DEPTH>
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where
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H: Hashable + Clone,
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{
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if self.size() == 0 {
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Frontier::empty()
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} else {
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let ommers_iter = self.parents.iter().filter_map(|v| v.as_ref()).cloned();
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let (leaf, ommers) = match (self.left.as_ref(), self.right.as_ref()) {
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(Some(a), None) => (a.clone(), ommers_iter.collect()),
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(Some(a), Some(b)) => (
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b.clone(),
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Some(a.clone()).into_iter().chain(ommers_iter).collect(),
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),
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_ => unreachable!(),
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};
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// If a frontier cannot be successfully constructed from the
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// parts of a commitment tree, it is a programming error.
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Frontier::from_parts((self.size() - 1).into(), leaf, ommers)
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.expect("Frontier should be constructable from CommitmentTree.")
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}
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}
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/// Returns the number of leaf nodes in the tree.
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pub fn size(&self) -> usize {
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self.parents.iter().enumerate().fold(
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match (self.left.as_ref(), self.right.as_ref()) {
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(None, None) => 0,
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(Some(_), None) => 1,
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(Some(_), Some(_)) => 2,
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(None, Some(_)) => unreachable!(),
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},
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|acc, (i, p)| {
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// Treat occupation of parents array as a binary number
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// (right-shifted by 1)
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acc + if p.is_some() { 1 << (i + 1) } else { 0 }
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},
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)
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}
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pub(crate) fn is_complete(&self, depth: u8) -> bool {
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if depth == 0 {
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self.left.is_some() && self.right.is_none() && self.parents.is_empty()
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} else {
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self.left.is_some()
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&& self.right.is_some()
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&& self
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.parents
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.iter()
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.chain(repeat(&None))
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.take((depth - 1).into())
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.all(|p| p.is_some())
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}
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}
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}
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#[cfg(feature = "legacy-api")]
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impl<H: Hashable + Clone, const DEPTH: u8> CommitmentTree<H, DEPTH> {
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/// Adds a leaf node to the tree.
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///
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/// Returns an error if the tree is full.
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#[allow(clippy::result_unit_err)]
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pub fn append(&mut self, node: H) -> Result<(), ()> {
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if self.is_complete(DEPTH) {
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// Tree is full
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return Err(());
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}
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match (&self.left, &self.right) {
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(None, _) => self.left = Some(node),
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(_, None) => self.right = Some(node),
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(Some(l), Some(r)) => {
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let mut combined = H::combine(0.into(), l, r);
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self.left = Some(node);
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self.right = None;
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for i in 0..DEPTH {
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let i_usize = usize::from(i);
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if i_usize < self.parents.len() {
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if let Some(p) = &self.parents[i_usize] {
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combined = H::combine((i + 1).into(), p, &combined);
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self.parents[i_usize] = None;
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} else {
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self.parents[i_usize] = Some(combined);
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break;
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}
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} else {
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self.parents.push(Some(combined));
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break;
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}
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}
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}
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}
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Ok(())
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}
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/// Returns the current root of the tree.
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pub fn root(&self) -> H {
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self.root_inner(DEPTH, PathFiller::empty())
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}
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pub(crate) fn root_inner(&self, depth: u8, mut filler: PathFiller<H>) -> H {
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assert!(depth > 0);
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// 1) Hash left and right leaves together.
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// - Empty leaves are used as needed.
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// - Note that `filler.next` is side-effecting and so cannot be factored out.
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let leaf_root = H::combine(
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0.into(),
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&self
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.left
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.as_ref()
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.map_or_else(|| filler.next(0.into()), |n| n.clone()),
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&self
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.right
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.as_ref()
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.map_or_else(|| filler.next(0.into()), |n| n.clone()),
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);
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// 2) Extend the parents to the desired depth with None values, then hash from leaf to
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// root. Roots of the empty subtrees are used as needed.
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self.parents
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.iter()
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.chain(repeat(&None))
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.take((depth - 1).into())
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.enumerate()
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.fold(leaf_root, |root, (i, p)| {
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let level = Level::from(i as u8 + 1);
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match p {
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Some(node) => H::combine(level, node, &root),
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None => H::combine(level, &root, &filler.next(level)),
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}
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})
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}
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}
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#[cfg(feature = "test-dependencies")]
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pub mod testing {
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use crate::Hashable;
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use core::fmt::Debug;
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use proptest::prelude::*;
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use std::collections::hash_map::DefaultHasher;
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use std::hash::Hasher;
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use crate::{Hashable, Level};
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impl<H: Hashable + Clone, const DEPTH: u8> crate::testing::Frontier<H>
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for super::Frontier<H, DEPTH>
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@ -259,12 +480,65 @@ pub mod testing {
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super::Frontier::root(self)
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}
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}
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#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
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pub struct TestNode(pub u64);
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impl Hashable for TestNode {
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fn empty_leaf() -> Self {
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Self(0)
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}
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fn combine(level: Level, a: &Self, b: &Self) -> Self {
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let mut hasher = DefaultHasher::new();
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hasher.write_u8(level.into());
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hasher.write_u64(a.0);
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hasher.write_u64(b.0);
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Self(hasher.finish())
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}
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}
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prop_compose! {
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pub fn arb_test_node()(i in any::<u64>()) -> TestNode {
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TestNode(i)
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}
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}
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#[cfg(feature = "legacy-api")]
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use {crate::frontier::CommitmentTree, proptest::collection::vec};
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#[cfg(feature = "legacy-api")]
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pub fn arb_commitment_tree<
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H: Hashable + Clone + Debug,
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T: Strategy<Value = H>,
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const DEPTH: u8,
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>(
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min_size: usize,
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arb_node: T,
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) -> impl Strategy<Value = CommitmentTree<H, DEPTH>> {
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assert!((1 << DEPTH) >= min_size + 100);
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vec(arb_node, min_size..(min_size + 100)).prop_map(move |v| {
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let mut tree = CommitmentTree::empty();
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for node in v.into_iter() {
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tree.append(node).unwrap();
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}
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tree.parents.resize_with((DEPTH - 1).into(), || None);
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tree
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})
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[cfg(feature = "legacy-api")]
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use {
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super::testing::{arb_commitment_tree, arb_test_node, TestNode},
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proptest::prelude::*,
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};
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#[test]
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fn nonempty_frontier_root() {
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let mut frontier = NonEmptyFrontier::new("a".to_string());
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@ -319,4 +593,73 @@ mod tests {
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frontier.witness(4, bridge_value_at)
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);
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}
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#[test]
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#[cfg(feature = "legacy-api")]
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fn test_commitment_tree_complete() {
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let mut t: CommitmentTree<TestNode, 6> = CommitmentTree::empty();
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for n in 1u64..=32 {
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t.append(TestNode(n)).unwrap();
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// every tree of a power-of-two height is complete
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let is_complete = n.count_ones() == 1;
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let level = usize::BITS - 1 - n.leading_zeros(); //log2
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assert_eq!(
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is_complete,
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t.is_complete(level.try_into().unwrap()),
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"Tree {:?} {} complete at height {}",
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t,
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if is_complete {
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"should be"
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} else {
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"should not be"
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},
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n
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);
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}
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}
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#[test]
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#[cfg(feature = "legacy-api")]
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fn test_commitment_tree_roundtrip() {
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let ct = CommitmentTree {
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left: Some("a".to_string()),
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right: Some("b".to_string()),
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parents: vec![
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Some("c".to_string()),
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Some("d".to_string()),
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Some("e".to_string()),
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Some("f".to_string()),
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None,
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None,
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None,
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],
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};
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let frontier: Frontier<String, 8> = ct.to_frontier();
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let ct0 = CommitmentTree::from_frontier(&frontier);
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assert_eq!(ct, ct0);
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let frontier0: Frontier<String, 8> = ct0.to_frontier();
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assert_eq!(frontier, frontier0);
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}
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#[cfg(feature = "legacy-api")]
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proptest! {
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#[test]
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fn prop_commitment_tree_roundtrip(ct in arb_commitment_tree(32, arb_test_node())) {
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let frontier: Frontier<TestNode, 8> = ct.to_frontier();
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let ct0 = CommitmentTree::from_frontier(&frontier);
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assert_eq!(ct, ct0);
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let frontier0: Frontier<TestNode, 8> = ct0.to_frontier();
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assert_eq!(frontier, frontier0);
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}
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#[test]
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fn prop_commitment_tree_roundtrip_str(ct in arb_commitment_tree::<_, _, 8>(32, any::<char>().prop_map(|c| c.to_string()))) {
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let frontier: Frontier<String, 8> = ct.to_frontier();
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let ct0 = CommitmentTree::from_frontier(&frontier);
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assert_eq!(ct, ct0);
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let frontier0: Frontier<String, 8> = ct0.to_frontier();
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assert_eq!(frontier, frontier0);
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}
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}
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}
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@ -8,6 +8,9 @@ use std::ops::{Add, AddAssign, Range, Sub};
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pub mod frontier;
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#[cfg(feature = "legacy-api")]
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pub mod witness;
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#[cfg(feature = "test-dependencies")]
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pub mod testing;
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@ -219,6 +222,13 @@ impl From<Level> for usize {
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}
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}
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impl TryFrom<usize> for Level {
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type Error = TryFromIntError;
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fn try_from(sz: usize) -> Result<Self, Self::Error> {
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<u8>::try_from(sz).map(Self)
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}
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}
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impl Sub<u8> for Level {
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type Output = Self;
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fn sub(self, value: u8) -> Self {
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|
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@ -0,0 +1,239 @@
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use std::convert::TryInto;
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use std::iter::repeat;
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use crate::{
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frontier::{CommitmentTree, PathFiller},
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Hashable, Level,
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};
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/// A path from a position in a particular commitment tree to the root of that tree.
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub struct MerklePath<H, const DEPTH: u8> {
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auth_path: Vec<(H, bool)>,
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position: u64,
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}
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impl<H, const DEPTH: u8> MerklePath<H, DEPTH> {
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pub fn auth_path(&self) -> &[(H, bool)] {
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&self.auth_path
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}
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pub fn position(&self) -> u64 {
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self.position
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}
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/// Constructs a Merkle path directly from a path and position.
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pub fn from_path(auth_path: Vec<(H, bool)>, position: u64) -> Result<Self, ()> {
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if auth_path.len() == usize::from(DEPTH) {
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Ok(MerklePath {
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auth_path,
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position,
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})
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} else {
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Err(())
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}
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}
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}
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impl<H: Hashable, const DEPTH: u8> MerklePath<H, DEPTH> {
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/// Returns the root of the tree corresponding to this path applied to `leaf`.
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pub fn root(&self, leaf: H) -> H {
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self.auth_path
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.iter()
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.enumerate()
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.fold(leaf, |root, (i, (p, leaf_is_on_right))| {
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let level = u8::try_from(i)
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.expect("Parents list length may not exceed what is representable by an u8")
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.into();
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match leaf_is_on_right {
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false => H::combine(level, &root, p),
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true => H::combine(level, p, &root),
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}
|
||||
})
|
||||
}
|
||||
}
|
||||
|
||||
/// An updatable witness to a path from a position in a particular [`CommitmentTree`].
|
||||
///
|
||||
/// Appending the same commitments in the same order to both the original
|
||||
/// [`CommitmentTree`] and this `IncrementalWitness` will result in a witness to the path
|
||||
/// from the target position to the root of the updated tree.
|
||||
///
|
||||
/// # Examples
|
||||
///
|
||||
/// ```
|
||||
/// use incrementalmerkletree::{
|
||||
/// frontier::{CommitmentTree, testing::TestNode},
|
||||
/// witness::IncrementalWitness,
|
||||
/// };
|
||||
///
|
||||
/// let mut tree = CommitmentTree::<TestNode, 8>::empty();
|
||||
///
|
||||
/// tree.append(TestNode(0));
|
||||
/// tree.append(TestNode(1));
|
||||
/// let mut witness = IncrementalWitness::from_tree(tree.clone());
|
||||
/// assert_eq!(witness.position(), 1);
|
||||
/// assert_eq!(tree.root(), witness.root());
|
||||
///
|
||||
/// let next = TestNode(2);
|
||||
/// tree.append(next.clone());
|
||||
/// witness.append(next);
|
||||
/// assert_eq!(tree.root(), witness.root());
|
||||
/// ```
|
||||
#[derive(Clone, Debug)]
|
||||
pub struct IncrementalWitness<H, const DEPTH: u8> {
|
||||
tree: CommitmentTree<H, DEPTH>,
|
||||
filled: Vec<H>,
|
||||
cursor_depth: u8,
|
||||
cursor: Option<CommitmentTree<H, DEPTH>>,
|
||||
}
|
||||
|
||||
impl<H, const DEPTH: u8> IncrementalWitness<H, DEPTH> {
|
||||
/// Creates an `IncrementalWitness` for the most recent commitment added to the given
|
||||
/// [`CommitmentTree`].
|
||||
pub fn from_tree(tree: CommitmentTree<H, DEPTH>) -> IncrementalWitness<H, DEPTH> {
|
||||
IncrementalWitness {
|
||||
tree,
|
||||
filled: vec![],
|
||||
cursor_depth: 0,
|
||||
cursor: None,
|
||||
}
|
||||
}
|
||||
|
||||
/// Returns the position of the witnessed leaf node in the commitment tree.
|
||||
pub fn position(&self) -> usize {
|
||||
self.tree.size() - 1
|
||||
}
|
||||
|
||||
/// Finds the next "depth" of an unfilled subtree.
|
||||
fn next_depth(&self) -> u8 {
|
||||
let mut skip: u8 = self
|
||||
.filled
|
||||
.len()
|
||||
.try_into()
|
||||
.expect("Merkle tree depths may not exceed the bounds of a u8");
|
||||
|
||||
if self.tree.left.is_none() {
|
||||
if skip > 0 {
|
||||
skip -= 1;
|
||||
} else {
|
||||
return 0;
|
||||
}
|
||||
}
|
||||
|
||||
if self.tree.right.is_none() {
|
||||
if skip > 0 {
|
||||
skip -= 1;
|
||||
} else {
|
||||
return 0;
|
||||
}
|
||||
}
|
||||
|
||||
let mut d = 1;
|
||||
for p in &self.tree.parents {
|
||||
if p.is_none() {
|
||||
if skip > 0 {
|
||||
skip -= 1;
|
||||
} else {
|
||||
return d;
|
||||
}
|
||||
}
|
||||
d += 1;
|
||||
}
|
||||
|
||||
d + skip
|
||||
}
|
||||
}
|
||||
|
||||
impl<H: Hashable + Clone, const DEPTH: u8> IncrementalWitness<H, DEPTH> {
|
||||
fn filler(&self) -> PathFiller<H> {
|
||||
let cursor_root = self
|
||||
.cursor
|
||||
.as_ref()
|
||||
.map(|c| c.root_inner(self.cursor_depth, PathFiller::empty()));
|
||||
|
||||
PathFiller {
|
||||
queue: self.filled.iter().cloned().chain(cursor_root).collect(),
|
||||
}
|
||||
}
|
||||
|
||||
/// Tracks a leaf node that has been added to the underlying tree.
|
||||
///
|
||||
/// Returns an error if the tree is full.
|
||||
#[allow(clippy::result_unit_err)]
|
||||
pub fn append(&mut self, node: H) -> Result<(), ()> {
|
||||
if let Some(mut cursor) = self.cursor.take() {
|
||||
cursor.append(node).expect("cursor should not be full");
|
||||
if cursor.is_complete(self.cursor_depth) {
|
||||
self.filled
|
||||
.push(cursor.root_inner(self.cursor_depth, PathFiller::empty()));
|
||||
} else {
|
||||
self.cursor = Some(cursor);
|
||||
}
|
||||
} else {
|
||||
self.cursor_depth = self.next_depth();
|
||||
if self.cursor_depth >= DEPTH {
|
||||
// Tree is full
|
||||
return Err(());
|
||||
}
|
||||
|
||||
if self.cursor_depth == 0 {
|
||||
self.filled.push(node);
|
||||
} else {
|
||||
let mut cursor = CommitmentTree::empty();
|
||||
cursor.append(node).expect("cursor should not be full");
|
||||
self.cursor = Some(cursor);
|
||||
}
|
||||
}
|
||||
|
||||
Ok(())
|
||||
}
|
||||
|
||||
/// Returns the current root of the tree corresponding to the witness.
|
||||
pub fn root(&self) -> H {
|
||||
self.root_inner(DEPTH)
|
||||
}
|
||||
|
||||
fn root_inner(&self, depth: u8) -> H {
|
||||
self.tree.root_inner(depth, self.filler())
|
||||
}
|
||||
|
||||
/// Returns the current witness, or None if the tree is empty.
|
||||
pub fn path(&self) -> Option<MerklePath<H, DEPTH>> {
|
||||
self.path_inner(DEPTH)
|
||||
}
|
||||
|
||||
fn path_inner(&self, depth: u8) -> Option<MerklePath<H, DEPTH>> {
|
||||
let mut filler = self.filler();
|
||||
let mut auth_path = Vec::new();
|
||||
|
||||
if let Some(node) = &self.tree.left {
|
||||
if self.tree.right.is_some() {
|
||||
auth_path.push((node.clone(), true));
|
||||
} else {
|
||||
auth_path.push((filler.next(0.into()), false));
|
||||
}
|
||||
} else {
|
||||
// Can't create an authentication path for the beginning of the tree
|
||||
return None;
|
||||
}
|
||||
|
||||
for (i, p) in self
|
||||
.tree
|
||||
.parents
|
||||
.iter()
|
||||
.chain(repeat(&None))
|
||||
.take((depth - 1).into())
|
||||
.enumerate()
|
||||
{
|
||||
auth_path.push(match p {
|
||||
Some(node) => (node.clone(), true),
|
||||
None => (filler.next(Level::from((i + 1) as u8)), false),
|
||||
});
|
||||
}
|
||||
|
||||
assert_eq!(auth_path.len(), usize::from(depth));
|
||||
|
||||
MerklePath::from_path(auth_path, self.position() as u64).ok()
|
||||
}
|
||||
}
|
||||
Loading…
Reference in New Issue