miden_crypto/merkle/smt/full/mod.rs
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use alloc::{
collections::{BTreeMap, BTreeSet},
string::ToString,
vec::Vec,
};
use super::{
EmptySubtreeRoots, Felt, InnerNode, InnerNodeInfo, LeafIndex, MerkleError, MerklePath,
MutationSet, NodeIndex, Rpo256, RpoDigest, SparseMerkleTree, Word, EMPTY_WORD,
};
mod error;
pub use error::{SmtLeafError, SmtProofError};
mod leaf;
pub use leaf::SmtLeaf;
mod proof;
pub use proof::SmtProof;
use winter_utils::{ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable};
#[cfg(test)]
mod tests;
// CONSTANTS
// ================================================================================================
pub const SMT_DEPTH: u8 = 64;
// SMT
// ================================================================================================
/// Sparse Merkle tree mapping 256-bit keys to 256-bit values. Both keys and values are represented
/// by 4 field elements.
///
/// All leaves sit at depth 64. The most significant element of the key is used to identify the leaf
/// to which the key maps.
///
/// A leaf is either empty, or holds one or more key-value pairs. An empty leaf hashes to the empty
/// word. Otherwise, a leaf hashes to the hash of its key-value pairs, ordered by key first, value
/// second.
#[derive(Debug, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
pub struct Smt {
root: RpoDigest,
leaves: BTreeMap<u64, SmtLeaf>,
inner_nodes: BTreeMap<NodeIndex, InnerNode>,
}
impl Smt {
// CONSTANTS
// --------------------------------------------------------------------------------------------
/// The default value used to compute the hash of empty leaves
pub const EMPTY_VALUE: Word = <Self as SparseMerkleTree<SMT_DEPTH>>::EMPTY_VALUE;
// CONSTRUCTORS
// --------------------------------------------------------------------------------------------
/// Returns a new [Smt].
///
/// All leaves in the returned tree are set to [Self::EMPTY_VALUE].
pub fn new() -> Self {
let root = *EmptySubtreeRoots::entry(SMT_DEPTH, 0);
Self {
root,
leaves: BTreeMap::new(),
inner_nodes: BTreeMap::new(),
}
}
/// Returns a new [Smt] instantiated with leaves set as specified by the provided entries.
///
/// All leaves omitted from the entries list are set to [Self::EMPTY_VALUE].
///
/// # Errors
/// Returns an error if the provided entries contain multiple values for the same key.
pub fn with_entries(
entries: impl IntoIterator<Item = (RpoDigest, Word)>,
) -> Result<Self, MerkleError> {
// create an empty tree
let mut tree = Self::new();
// This being a sparse data structure, the EMPTY_WORD is not assigned to the `BTreeMap`, so
// entries with the empty value need additional tracking.
let mut key_set_to_zero = BTreeSet::new();
for (key, value) in entries {
let old_value = tree.insert(key, value);
if old_value != EMPTY_WORD || key_set_to_zero.contains(&key) {
return Err(MerkleError::DuplicateValuesForIndex(
LeafIndex::<SMT_DEPTH>::from(key).value(),
));
}
if value == EMPTY_WORD {
key_set_to_zero.insert(key);
};
}
Ok(tree)
}
// PUBLIC ACCESSORS
// --------------------------------------------------------------------------------------------
/// Returns the depth of the tree
pub const fn depth(&self) -> u8 {
SMT_DEPTH
}
/// Returns the root of the tree
pub fn root(&self) -> RpoDigest {
<Self as SparseMerkleTree<SMT_DEPTH>>::root(self)
}
/// Returns the leaf to which `key` maps
pub fn get_leaf(&self, key: &RpoDigest) -> SmtLeaf {
<Self as SparseMerkleTree<SMT_DEPTH>>::get_leaf(self, key)
}
/// Returns the value associated with `key`
pub fn get_value(&self, key: &RpoDigest) -> Word {
<Self as SparseMerkleTree<SMT_DEPTH>>::get_value(self, key)
}
/// Returns an opening of the leaf associated with `key`. Conceptually, an opening is a Merkle
/// path to the leaf, as well as the leaf itself.
pub fn open(&self, key: &RpoDigest) -> SmtProof {
<Self as SparseMerkleTree<SMT_DEPTH>>::open(self, key)
}
/// Returns a boolean value indicating whether the SMT is empty.
pub fn is_empty(&self) -> bool {
debug_assert_eq!(self.leaves.is_empty(), self.root == Self::EMPTY_ROOT);
self.root == Self::EMPTY_ROOT
}
// ITERATORS
// --------------------------------------------------------------------------------------------
/// Returns an iterator over the leaves of this [Smt].
pub fn leaves(&self) -> impl Iterator<Item = (LeafIndex<SMT_DEPTH>, &SmtLeaf)> {
self.leaves
.iter()
.map(|(leaf_index, leaf)| (LeafIndex::new_max_depth(*leaf_index), leaf))
}
/// Returns an iterator over the key-value pairs of this [Smt].
pub fn entries(&self) -> impl Iterator<Item = &(RpoDigest, Word)> {
self.leaves().flat_map(|(_, leaf)| leaf.entries())
}
/// Returns an iterator over the inner nodes of this [Smt].
pub fn inner_nodes(&self) -> impl Iterator<Item = InnerNodeInfo> + '_ {
self.inner_nodes.values().map(|e| InnerNodeInfo {
value: e.hash(),
left: e.left,
right: e.right,
})
}
// STATE MUTATORS
// --------------------------------------------------------------------------------------------
/// Inserts a value at the specified key, returning the previous value associated with that key.
/// Recall that by definition, any key that hasn't been updated is associated with
/// [`Self::EMPTY_VALUE`].
///
/// This also recomputes all hashes between the leaf (associated with the key) and the root,
/// updating the root itself.
pub fn insert(&mut self, key: RpoDigest, value: Word) -> Word {
<Self as SparseMerkleTree<SMT_DEPTH>>::insert(self, key, value)
}
/// Computes what changes are necessary to insert the specified key-value pairs into this Merkle
/// tree, allowing for validation before applying those changes.
///
/// This method returns a [`MutationSet`], which contains all the information for inserting
/// `kv_pairs` into this Merkle tree already calculated, including the new root hash, which can
/// be queried with [`MutationSet::root()`]. Once a mutation set is returned,
/// [`Smt::apply_mutations()`] can be called in order to commit these changes to the Merkle
/// tree, or [`drop()`] to discard them.
///
/// # Example
/// ```
/// # use miden_crypto::{hash::rpo::RpoDigest, Felt, Word};
/// # use miden_crypto::merkle::{Smt, EmptySubtreeRoots, SMT_DEPTH};
/// let mut smt = Smt::new();
/// let pair = (RpoDigest::default(), Word::default());
/// let mutations = smt.compute_mutations(vec![pair]);
/// assert_eq!(mutations.root(), *EmptySubtreeRoots::entry(SMT_DEPTH, 0));
/// smt.apply_mutations(mutations);
/// assert_eq!(smt.root(), *EmptySubtreeRoots::entry(SMT_DEPTH, 0));
/// ```
pub fn compute_mutations(
&self,
kv_pairs: impl IntoIterator<Item = (RpoDigest, Word)>,
) -> MutationSet<SMT_DEPTH, RpoDigest, Word> {
<Self as SparseMerkleTree<SMT_DEPTH>>::compute_mutations(self, kv_pairs)
}
/// Apply the prospective mutations computed with [`Smt::compute_mutations()`] to this tree.
///
/// # Errors
/// If `mutations` was computed on a tree with a different root than this one, returns
/// [`MerkleError::ConflictingRoots`] with a two-item [`Vec`]. The first item is the root hash
/// the `mutations` were computed against, and the second item is the actual current root of
/// this tree.
pub fn apply_mutations(
&mut self,
mutations: MutationSet<SMT_DEPTH, RpoDigest, Word>,
) -> Result<(), MerkleError> {
<Self as SparseMerkleTree<SMT_DEPTH>>::apply_mutations(self, mutations)
}
// HELPERS
// --------------------------------------------------------------------------------------------
/// Inserts `value` at leaf index pointed to by `key`. `value` is guaranteed to not be the empty
/// value, such that this is indeed an insertion.
fn perform_insert(&mut self, key: RpoDigest, value: Word) -> Option<Word> {
debug_assert_ne!(value, Self::EMPTY_VALUE);
let leaf_index: LeafIndex<SMT_DEPTH> = Self::key_to_leaf_index(&key);
match self.leaves.get_mut(&leaf_index.value()) {
Some(leaf) => leaf.insert(key, value),
None => {
self.leaves.insert(leaf_index.value(), SmtLeaf::Single((key, value)));
None
},
}
}
/// Removes key-value pair at leaf index pointed to by `key` if it exists.
fn perform_remove(&mut self, key: RpoDigest) -> Option<Word> {
let leaf_index: LeafIndex<SMT_DEPTH> = Self::key_to_leaf_index(&key);
if let Some(leaf) = self.leaves.get_mut(&leaf_index.value()) {
let (old_value, is_empty) = leaf.remove(key);
if is_empty {
self.leaves.remove(&leaf_index.value());
}
old_value
} else {
// there's nothing stored at the leaf; nothing to update
None
}
}
}
impl SparseMerkleTree<SMT_DEPTH> for Smt {
type Key = RpoDigest;
type Value = Word;
type Leaf = SmtLeaf;
type Opening = SmtProof;
const EMPTY_VALUE: Self::Value = EMPTY_WORD;
const EMPTY_ROOT: RpoDigest = *EmptySubtreeRoots::entry(SMT_DEPTH, 0);
fn root(&self) -> RpoDigest {
self.root
}
fn set_root(&mut self, root: RpoDigest) {
self.root = root;
}
fn get_inner_node(&self, index: NodeIndex) -> InnerNode {
self.inner_nodes
.get(&index)
.cloned()
.unwrap_or_else(|| EmptySubtreeRoots::get_inner_node(SMT_DEPTH, index.depth()))
}
fn insert_inner_node(&mut self, index: NodeIndex, inner_node: InnerNode) {
self.inner_nodes.insert(index, inner_node);
}
fn remove_inner_node(&mut self, index: NodeIndex) {
let _ = self.inner_nodes.remove(&index);
}
fn insert_value(&mut self, key: Self::Key, value: Self::Value) -> Option<Self::Value> {
// inserting an `EMPTY_VALUE` is equivalent to removing any value associated with `key`
if value != Self::EMPTY_VALUE {
self.perform_insert(key, value)
} else {
self.perform_remove(key)
}
}
fn get_value(&self, key: &Self::Key) -> Self::Value {
let leaf_pos = LeafIndex::<SMT_DEPTH>::from(*key).value();
match self.leaves.get(&leaf_pos) {
Some(leaf) => leaf.get_value(key).unwrap_or_default(),
None => EMPTY_WORD,
}
}
fn get_leaf(&self, key: &RpoDigest) -> Self::Leaf {
let leaf_pos = LeafIndex::<SMT_DEPTH>::from(*key).value();
match self.leaves.get(&leaf_pos) {
Some(leaf) => leaf.clone(),
None => SmtLeaf::new_empty(key.into()),
}
}
fn hash_leaf(leaf: &Self::Leaf) -> RpoDigest {
leaf.hash()
}
fn construct_prospective_leaf(
&self,
mut existing_leaf: SmtLeaf,
key: &RpoDigest,
value: &Word,
) -> SmtLeaf {
debug_assert_eq!(existing_leaf.index(), Self::key_to_leaf_index(key));
match existing_leaf {
SmtLeaf::Empty(_) => SmtLeaf::new_single(*key, *value),
_ => {
if *value != EMPTY_WORD {
existing_leaf.insert(*key, *value);
} else {
existing_leaf.remove(*key);
}
existing_leaf
},
}
}
fn key_to_leaf_index(key: &RpoDigest) -> LeafIndex<SMT_DEPTH> {
let most_significant_felt = key[3];
LeafIndex::new_max_depth(most_significant_felt.as_int())
}
fn path_and_leaf_to_opening(path: MerklePath, leaf: SmtLeaf) -> SmtProof {
SmtProof::new_unchecked(path, leaf)
}
}
impl Default for Smt {
fn default() -> Self {
Self::new()
}
}
// CONVERSIONS
// ================================================================================================
impl From<Word> for LeafIndex<SMT_DEPTH> {
fn from(value: Word) -> Self {
// We use the most significant `Felt` of a `Word` as the leaf index.
Self::new_max_depth(value[3].as_int())
}
}
impl From<RpoDigest> for LeafIndex<SMT_DEPTH> {
fn from(value: RpoDigest) -> Self {
Word::from(value).into()
}
}
impl From<&RpoDigest> for LeafIndex<SMT_DEPTH> {
fn from(value: &RpoDigest) -> Self {
Word::from(value).into()
}
}
// SERIALIZATION
// ================================================================================================
impl Serializable for Smt {
fn write_into<W: ByteWriter>(&self, target: &mut W) {
// Write the number of filled leaves for this Smt
target.write_usize(self.entries().count());
// Write each (key, value) pair
for (key, value) in self.entries() {
target.write(key);
target.write(value);
}
}
fn get_size_hint(&self) -> usize {
let entries_count = self.entries().count();
// Each entry is the size of a digest plus a word.
entries_count.get_size_hint()
+ entries_count * (RpoDigest::SERIALIZED_SIZE + EMPTY_WORD.get_size_hint())
}
}
impl Deserializable for Smt {
fn read_from<R: ByteReader>(source: &mut R) -> Result<Self, DeserializationError> {
// Read the number of filled leaves for this Smt
let num_filled_leaves = source.read_usize()?;
let mut entries = Vec::with_capacity(num_filled_leaves);
for _ in 0..num_filled_leaves {
let key = source.read()?;
let value = source.read()?;
entries.push((key, value));
}
Self::with_entries(entries)
.map_err(|err| DeserializationError::InvalidValue(err.to_string()))
}
}
#[test]
fn test_smt_serialization_deserialization() {
// Smt for default types (empty map)
let smt_default = Smt::default();
let bytes = smt_default.to_bytes();
assert_eq!(smt_default, Smt::read_from_bytes(&bytes).unwrap());
assert_eq!(bytes.len(), smt_default.get_size_hint());
// Smt with values
let smt_leaves_2: [(RpoDigest, Word); 2] = [
(
RpoDigest::new([Felt::new(101), Felt::new(102), Felt::new(103), Felt::new(104)]),
[Felt::new(1_u64), Felt::new(2_u64), Felt::new(3_u64), Felt::new(4_u64)],
),
(
RpoDigest::new([Felt::new(105), Felt::new(106), Felt::new(107), Felt::new(108)]),
[Felt::new(5_u64), Felt::new(6_u64), Felt::new(7_u64), Felt::new(8_u64)],
),
];
let smt = Smt::with_entries(smt_leaves_2).unwrap();
let bytes = smt.to_bytes();
assert_eq!(smt, Smt::read_from_bytes(&bytes).unwrap());
assert_eq!(bytes.len(), smt.get_size_hint());
}