miden_crypto/merkle/partial_mt/mod.rs
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use alloc::{
collections::{BTreeMap, BTreeSet},
string::String,
vec::Vec,
};
use core::fmt;
use super::{
InnerNodeInfo, MerkleError, MerklePath, NodeIndex, Rpo256, RpoDigest, ValuePath, Word,
EMPTY_WORD,
};
use crate::utils::{
word_to_hex, ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable,
};
#[cfg(test)]
mod tests;
// CONSTANTS
// ================================================================================================
/// Index of the root node.
const ROOT_INDEX: NodeIndex = NodeIndex::root();
/// An RpoDigest consisting of 4 ZERO elements.
const EMPTY_DIGEST: RpoDigest = RpoDigest::new(EMPTY_WORD);
// PARTIAL MERKLE TREE
// ================================================================================================
/// A partial Merkle tree with NodeIndex keys and 4-element RpoDigest leaf values. Partial Merkle
/// Tree allows to create Merkle Tree by providing Merkle paths of different lengths.
///
/// The root of the tree is recomputed on each new leaf update.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
pub struct PartialMerkleTree {
max_depth: u8,
nodes: BTreeMap<NodeIndex, RpoDigest>,
leaves: BTreeSet<NodeIndex>,
}
impl Default for PartialMerkleTree {
fn default() -> Self {
Self::new()
}
}
impl PartialMerkleTree {
// CONSTANTS
// --------------------------------------------------------------------------------------------
/// Minimum supported depth.
pub const MIN_DEPTH: u8 = 1;
/// Maximum supported depth.
pub const MAX_DEPTH: u8 = 64;
// CONSTRUCTORS
// --------------------------------------------------------------------------------------------
/// Returns a new empty [PartialMerkleTree].
pub fn new() -> Self {
PartialMerkleTree {
max_depth: 0,
nodes: BTreeMap::new(),
leaves: BTreeSet::new(),
}
}
/// Appends the provided paths iterator into the set.
///
/// Analogous to [Self::add_path].
pub fn with_paths<I>(paths: I) -> Result<Self, MerkleError>
where
I: IntoIterator<Item = (u64, RpoDigest, MerklePath)>,
{
// create an empty tree
let tree = PartialMerkleTree::new();
paths.into_iter().try_fold(tree, |mut tree, (index, value, path)| {
tree.add_path(index, value, path)?;
Ok(tree)
})
}
/// Returns a new [PartialMerkleTree] instantiated with leaves map as specified by the provided
/// entries.
///
/// # Errors
/// Returns an error if:
/// - If the depth is 0 or is greater than 64.
/// - The number of entries exceeds the maximum tree capacity, that is 2^{depth}.
/// - The provided entries contain an insufficient set of nodes.
pub fn with_leaves<R, I>(entries: R) -> Result<Self, MerkleError>
where
R: IntoIterator<IntoIter = I>,
I: Iterator<Item = (NodeIndex, RpoDigest)> + ExactSizeIterator,
{
let mut layers: BTreeMap<u8, Vec<u64>> = BTreeMap::new();
let mut leaves = BTreeSet::new();
let mut nodes = BTreeMap::new();
// add data to the leaves and nodes maps and also fill layers map, where the key is the
// depth of the node and value is its index.
for (node_index, hash) in entries.into_iter() {
leaves.insert(node_index);
nodes.insert(node_index, hash);
layers
.entry(node_index.depth())
.and_modify(|layer_vec| layer_vec.push(node_index.value()))
.or_insert(vec![node_index.value()]);
}
// check if the number of leaves can be accommodated by the tree's depth; we use a min
// depth of 63 because we consider passing in a vector of size 2^64 infeasible.
let max = 2usize.pow(63);
if layers.len() > max {
return Err(MerkleError::InvalidNumEntries(max));
}
// Get maximum depth
let max_depth = *layers.keys().next_back().unwrap_or(&0);
// fill layers without nodes with empty vector
for depth in 0..max_depth {
layers.entry(depth).or_default();
}
let mut layer_iter = layers.into_values().rev();
let mut parent_layer = layer_iter.next().unwrap();
let mut current_layer;
for depth in (1..max_depth + 1).rev() {
// set current_layer = parent_layer and parent_layer = layer_iter.next()
current_layer = layer_iter.next().unwrap();
core::mem::swap(&mut current_layer, &mut parent_layer);
for index_value in current_layer {
// get the parent node index
let parent_node = NodeIndex::new(depth - 1, index_value / 2)?;
// Check if the parent hash was already calculated. In about half of the cases, we
// don't need to do anything.
if !parent_layer.contains(&parent_node.value()) {
// create current node index
let index = NodeIndex::new(depth, index_value)?;
// get hash of the current node
let node = nodes.get(&index).ok_or(MerkleError::NodeNotInSet(index))?;
// get hash of the sibling node
let sibling = nodes
.get(&index.sibling())
.ok_or(MerkleError::NodeNotInSet(index.sibling()))?;
// get parent hash
let parent = Rpo256::merge(&index.build_node(*node, *sibling));
// add index value of the calculated node to the parents layer
parent_layer.push(parent_node.value());
// add index and hash to the nodes map
nodes.insert(parent_node, parent);
}
}
}
Ok(PartialMerkleTree { max_depth, nodes, leaves })
}
// PUBLIC ACCESSORS
// --------------------------------------------------------------------------------------------
/// Returns the root of this Merkle tree.
pub fn root(&self) -> RpoDigest {
self.nodes.get(&ROOT_INDEX).cloned().unwrap_or(EMPTY_DIGEST)
}
/// Returns the depth of this Merkle tree.
pub fn max_depth(&self) -> u8 {
self.max_depth
}
/// Returns a node at the specified NodeIndex.
///
/// # Errors
/// Returns an error if the specified NodeIndex is not contained in the nodes map.
pub fn get_node(&self, index: NodeIndex) -> Result<RpoDigest, MerkleError> {
self.nodes.get(&index).ok_or(MerkleError::NodeNotInSet(index)).copied()
}
/// Returns true if provided index contains in the leaves set, false otherwise.
pub fn is_leaf(&self, index: NodeIndex) -> bool {
self.leaves.contains(&index)
}
/// Returns a vector of paths from every leaf to the root.
pub fn to_paths(&self) -> Vec<(NodeIndex, ValuePath)> {
let mut paths = Vec::new();
self.leaves.iter().for_each(|&leaf| {
paths.push((
leaf,
ValuePath {
value: self.get_node(leaf).expect("Failed to get leaf node"),
path: self.get_path(leaf).expect("Failed to get path"),
},
));
});
paths
}
/// Returns a Merkle path from the node at the specified index to the root.
///
/// The node itself is not included in the path.
///
/// # Errors
/// Returns an error if:
/// - the specified index has depth set to 0 or the depth is greater than the depth of this
/// Merkle tree.
/// - the specified index is not contained in the nodes map.
pub fn get_path(&self, mut index: NodeIndex) -> Result<MerklePath, MerkleError> {
if index.is_root() {
return Err(MerkleError::DepthTooSmall(index.depth()));
} else if index.depth() > self.max_depth() {
return Err(MerkleError::DepthTooBig(index.depth() as u64));
}
if !self.nodes.contains_key(&index) {
return Err(MerkleError::NodeNotInSet(index));
}
let mut path = Vec::new();
for _ in 0..index.depth() {
let sibling_index = index.sibling();
index.move_up();
let sibling =
self.nodes.get(&sibling_index).cloned().expect("Sibling node not in the map");
path.push(sibling);
}
Ok(MerklePath::new(path))
}
// ITERATORS
// --------------------------------------------------------------------------------------------
/// Returns an iterator over the leaves of this [PartialMerkleTree].
pub fn leaves(&self) -> impl Iterator<Item = (NodeIndex, RpoDigest)> + '_ {
self.leaves.iter().map(|&leaf| {
(
leaf,
self.get_node(leaf)
.unwrap_or_else(|_| panic!("Leaf with {leaf} is not in the nodes map")),
)
})
}
/// Returns an iterator over the inner nodes of this Merkle tree.
pub fn inner_nodes(&self) -> impl Iterator<Item = InnerNodeInfo> + '_ {
let inner_nodes = self.nodes.iter().filter(|(index, _)| !self.leaves.contains(index));
inner_nodes.map(|(index, digest)| {
let left_hash =
self.nodes.get(&index.left_child()).expect("Failed to get left child hash");
let right_hash =
self.nodes.get(&index.right_child()).expect("Failed to get right child hash");
InnerNodeInfo {
value: *digest,
left: *left_hash,
right: *right_hash,
}
})
}
// STATE MUTATORS
// --------------------------------------------------------------------------------------------
/// Adds the nodes of the specified Merkle path to this [PartialMerkleTree]. The `index_value`
/// and `value` parameters specify the leaf node at which the path starts.
///
/// # Errors
/// Returns an error if:
/// - The depth of the specified node_index is greater than 64 or smaller than 1.
/// - The specified path is not consistent with other paths in the set (i.e., resolves to a
/// different root).
pub fn add_path(
&mut self,
index_value: u64,
value: RpoDigest,
path: MerklePath,
) -> Result<(), MerkleError> {
let index_value = NodeIndex::new(path.len() as u8, index_value)?;
Self::check_depth(index_value.depth())?;
self.update_depth(index_value.depth());
// add provided node and its sibling to the leaves set
self.leaves.insert(index_value);
let sibling_node_index = index_value.sibling();
self.leaves.insert(sibling_node_index);
// add provided node and its sibling to the nodes map
self.nodes.insert(index_value, value);
self.nodes.insert(sibling_node_index, path[0]);
// traverse to the root, updating the nodes
let mut index_value = index_value;
let node = Rpo256::merge(&index_value.build_node(value, path[0]));
let root = path.iter().skip(1).copied().fold(node, |node, hash| {
index_value.move_up();
// insert calculated node to the nodes map
self.nodes.insert(index_value, node);
// if the calculated node was a leaf, remove it from leaves set.
self.leaves.remove(&index_value);
let sibling_node = index_value.sibling();
// Insert node from Merkle path to the nodes map. This sibling node becomes a leaf only
// if it is a new node (it wasn't in nodes map).
// Node can be in 3 states: internal node, leaf of the tree and not a tree node at all.
// - Internal node can only stay in this state -- addition of a new path can't make it
// a leaf or remove it from the tree.
// - Leaf node can stay in the same state (remain a leaf) or can become an internal
// node. In the first case we don't need to do anything, and the second case is handled
// by the call of `self.leaves.remove(&index_value);`
// - New node can be a calculated node or a "sibling" node from a Merkle Path:
// --- Calculated node, obviously, never can be a leaf.
// --- Sibling node can be only a leaf, because otherwise it is not a new node.
if self.nodes.insert(sibling_node, hash).is_none() {
self.leaves.insert(sibling_node);
}
Rpo256::merge(&index_value.build_node(node, hash))
});
// if the path set is empty (the root is all ZEROs), set the root to the root of the added
// path; otherwise, the root of the added path must be identical to the current root
if self.root() == EMPTY_DIGEST {
self.nodes.insert(ROOT_INDEX, root);
} else if self.root() != root {
return Err(MerkleError::ConflictingRoots([self.root(), root].to_vec()));
}
Ok(())
}
/// Updates value of the leaf at the specified index returning the old leaf value.
/// By default the specified index is assumed to belong to the deepest layer. If the considered
/// node does not belong to the tree, the first node on the way to the root will be changed.
///
/// By default the specified index is assumed to belong to the deepest layer. If the considered
/// node does not belong to the tree, the first node on the way to the root will be changed.
///
/// This also recomputes all hashes between the leaf and the root, updating the root itself.
///
/// # Errors
/// Returns an error if:
/// - The specified index is greater than the maximum number of nodes on the deepest layer.
pub fn update_leaf(&mut self, index: u64, value: Word) -> Result<RpoDigest, MerkleError> {
let mut node_index = NodeIndex::new(self.max_depth(), index)?;
// proceed to the leaf
for _ in 0..node_index.depth() {
if !self.leaves.contains(&node_index) {
node_index.move_up();
}
}
// add node value to the nodes Map
let old_value = self
.nodes
.insert(node_index, value.into())
.ok_or(MerkleError::NodeNotInSet(node_index))?;
// if the old value and new value are the same, there is nothing to update
if value == *old_value {
return Ok(old_value);
}
let mut value = value.into();
for _ in 0..node_index.depth() {
let sibling = self.nodes.get(&node_index.sibling()).expect("sibling should exist");
value = Rpo256::merge(&node_index.build_node(value, *sibling));
node_index.move_up();
self.nodes.insert(node_index, value);
}
Ok(old_value)
}
// UTILITY FUNCTIONS
// --------------------------------------------------------------------------------------------
/// Utility to visualize a [PartialMerkleTree] in text.
pub fn print(&self) -> Result<String, fmt::Error> {
let indent = " ";
let mut s = String::new();
s.push_str("root: ");
s.push_str(&word_to_hex(&self.root())?);
s.push('\n');
for d in 1..=self.max_depth() {
let entries = 2u64.pow(d.into());
for i in 0..entries {
let index = NodeIndex::new(d, i).expect("The index must always be valid");
let node = self.get_node(index);
let node = match node {
Err(_) => continue,
Ok(node) => node,
};
for _ in 0..d {
s.push_str(indent);
}
s.push_str(&format!("({}, {}): ", index.depth(), index.value()));
s.push_str(&word_to_hex(&node)?);
s.push('\n');
}
}
Ok(s)
}
// HELPER METHODS
// --------------------------------------------------------------------------------------------
/// Updates depth value with the maximum of current and provided depth.
fn update_depth(&mut self, new_depth: u8) {
self.max_depth = new_depth.max(self.max_depth);
}
/// Returns an error if the depth is 0 or is greater than 64.
fn check_depth(depth: u8) -> Result<(), MerkleError> {
// validate the range of the depth.
if depth < Self::MIN_DEPTH {
return Err(MerkleError::DepthTooSmall(depth));
} else if Self::MAX_DEPTH < depth {
return Err(MerkleError::DepthTooBig(depth as u64));
}
Ok(())
}
}
// SERIALIZATION
// ================================================================================================
impl Serializable for PartialMerkleTree {
fn write_into<W: ByteWriter>(&self, target: &mut W) {
// write leaf nodes
target.write_u64(self.leaves.len() as u64);
for leaf_index in self.leaves.iter() {
leaf_index.write_into(target);
self.get_node(*leaf_index).expect("Leaf hash not found").write_into(target);
}
}
}
impl Deserializable for PartialMerkleTree {
fn read_from<R: ByteReader>(source: &mut R) -> Result<Self, DeserializationError> {
let leaves_len = source.read_u64()? as usize;
let mut leaf_nodes = Vec::with_capacity(leaves_len);
// add leaf nodes to the vector
for _ in 0..leaves_len {
let index = NodeIndex::read_from(source)?;
let hash = RpoDigest::read_from(source)?;
leaf_nodes.push((index, hash));
}
let pmt = PartialMerkleTree::with_leaves(leaf_nodes).map_err(|_| {
DeserializationError::InvalidValue("Invalid data for PartialMerkleTree creation".into())
})?;
Ok(pmt)
}
}