miden-crypto/src/merkle/smt/full/mod.rs
src/merkle/smt/full/mod.rsRaw
1use alloc::{
2 collections::{BTreeMap, BTreeSet},
3 string::ToString,
4 vec::Vec,
5};
6
7use super::{
8 EmptySubtreeRoots, Felt, InnerNode, InnerNodeInfo, LeafIndex, MerkleError, MerklePath,
9 MutationSet, NodeIndex, Rpo256, RpoDigest, SparseMerkleTree, Word, EMPTY_WORD,
10};
11
12mod error;
13pub use error::{SmtLeafError, SmtProofError};
14
15mod leaf;
16pub use leaf::SmtLeaf;
17
18mod proof;
19pub use proof::SmtProof;
20use winter_utils::{ByteReader, ByteWriter, Deserializable, DeserializationError, Serializable};
21
22#[cfg(test)]
23mod tests;
24
25// CONSTANTS
26// ================================================================================================
27
28pub const SMT_DEPTH: u8 = 64;
29
30// SMT
31// ================================================================================================
32
33/// Sparse Merkle tree mapping 256-bit keys to 256-bit values. Both keys and values are represented
34/// by 4 field elements.
35///
36/// All leaves sit at depth 64. The most significant element of the key is used to identify the leaf
37/// to which the key maps.
38///
39/// A leaf is either empty, or holds one or more key-value pairs. An empty leaf hashes to the empty
40/// word. Otherwise, a leaf hashes to the hash of its key-value pairs, ordered by key first, value
41/// second.
42#[derive(Debug, Clone, PartialEq, Eq)]
43#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
44pub struct Smt {
45 root: RpoDigest,
46 leaves: BTreeMap<u64, SmtLeaf>,
47 inner_nodes: BTreeMap<NodeIndex, InnerNode>,
48}
49
50impl Smt {
51 // CONSTANTS
52 // --------------------------------------------------------------------------------------------
53 /// The default value used to compute the hash of empty leaves
54 pub const EMPTY_VALUE: Word = <Self as SparseMerkleTree<SMT_DEPTH>>::EMPTY_VALUE;
55
56 // CONSTRUCTORS
57 // --------------------------------------------------------------------------------------------
58
59 /// Returns a new [Smt].
60 ///
61 /// All leaves in the returned tree are set to [Self::EMPTY_VALUE].
62 pub fn new() -> Self {
63 let root = *EmptySubtreeRoots::entry(SMT_DEPTH, 0);
64
65 Self {
66 root,
67 leaves: BTreeMap::new(),
68 inner_nodes: BTreeMap::new(),
69 }
70 }
71
72 /// Returns a new [Smt] instantiated with leaves set as specified by the provided entries.
73 ///
74 /// All leaves omitted from the entries list are set to [Self::EMPTY_VALUE].
75 ///
76 /// # Errors
77 /// Returns an error if the provided entries contain multiple values for the same key.
78 pub fn with_entries(
79 entries: impl IntoIterator<Item = (RpoDigest, Word)>,
80 ) -> Result<Self, MerkleError> {
81 // create an empty tree
82 let mut tree = Self::new();
83
84 // This being a sparse data structure, the EMPTY_WORD is not assigned to the `BTreeMap`, so
85 // entries with the empty value need additional tracking.
86 let mut key_set_to_zero = BTreeSet::new();
87
88 for (key, value) in entries {
89 let old_value = tree.insert(key, value);
90
91 if old_value != EMPTY_WORD || key_set_to_zero.contains(&key) {
92 return Err(MerkleError::DuplicateValuesForIndex(
93 LeafIndex::<SMT_DEPTH>::from(key).value(),
94 ));
95 }
96
97 if value == EMPTY_WORD {
98 key_set_to_zero.insert(key);
99 };
100 }
101 Ok(tree)
102 }
103
104 // PUBLIC ACCESSORS
105 // --------------------------------------------------------------------------------------------
106
107 /// Returns the depth of the tree
108 pub const fn depth(&self) -> u8 {
109 SMT_DEPTH
110 }
111
112 /// Returns the root of the tree
113 pub fn root(&self) -> RpoDigest {
114 <Self as SparseMerkleTree<SMT_DEPTH>>::root(self)
115 }
116
117 /// Returns the leaf to which `key` maps
118 pub fn get_leaf(&self, key: &RpoDigest) -> SmtLeaf {
119 <Self as SparseMerkleTree<SMT_DEPTH>>::get_leaf(self, key)
120 }
121
122 /// Returns the value associated with `key`
123 pub fn get_value(&self, key: &RpoDigest) -> Word {
124 <Self as SparseMerkleTree<SMT_DEPTH>>::get_value(self, key)
125 }
126
127 /// Returns an opening of the leaf associated with `key`. Conceptually, an opening is a Merkle
128 /// path to the leaf, as well as the leaf itself.
129 pub fn open(&self, key: &RpoDigest) -> SmtProof {
130 <Self as SparseMerkleTree<SMT_DEPTH>>::open(self, key)
131 }
132
133 // ITERATORS
134 // --------------------------------------------------------------------------------------------
135
136 /// Returns an iterator over the leaves of this [Smt].
137 pub fn leaves(&self) -> impl Iterator<Item = (LeafIndex<SMT_DEPTH>, &SmtLeaf)> {
138 self.leaves
139 .iter()
140 .map(|(leaf_index, leaf)| (LeafIndex::new_max_depth(*leaf_index), leaf))
141 }
142
143 /// Returns an iterator over the key-value pairs of this [Smt].
144 pub fn entries(&self) -> impl Iterator<Item = &(RpoDigest, Word)> {
145 self.leaves().flat_map(|(_, leaf)| leaf.entries())
146 }
147
148 /// Returns an iterator over the inner nodes of this [Smt].
149 pub fn inner_nodes(&self) -> impl Iterator<Item = InnerNodeInfo> + '_ {
150 self.inner_nodes.values().map(|e| InnerNodeInfo {
151 value: e.hash(),
152 left: e.left,
153 right: e.right,
154 })
155 }
156
157 // STATE MUTATORS
158 // --------------------------------------------------------------------------------------------
159
160 /// Inserts a value at the specified key, returning the previous value associated with that key.
161 /// Recall that by definition, any key that hasn't been updated is associated with
162 /// [`Self::EMPTY_VALUE`].
163 ///
164 /// This also recomputes all hashes between the leaf (associated with the key) and the root,
165 /// updating the root itself.
166 pub fn insert(&mut self, key: RpoDigest, value: Word) -> Word {
167 <Self as SparseMerkleTree<SMT_DEPTH>>::insert(self, key, value)
168 }
169
170 /// Computes what changes are necessary to insert the specified key-value pairs into this Merkle
171 /// tree, allowing for validation before applying those changes.
172 ///
173 /// This method returns a [`MutationSet`], which contains all the information for inserting
174 /// `kv_pairs` into this Merkle tree already calculated, including the new root hash, which can
175 /// be queried with [`MutationSet::root()`]. Once a mutation set is returned,
176 /// [`Smt::apply_mutations()`] can be called in order to commit these changes to the Merkle
177 /// tree, or [`drop()`] to discard them.
178 ///
179 /// # Example
180 /// ```
181 /// # use miden_crypto::{hash::rpo::RpoDigest, Felt, Word};
182 /// # use miden_crypto::merkle::{Smt, EmptySubtreeRoots, SMT_DEPTH};
183 /// let mut smt = Smt::new();
184 /// let pair = (RpoDigest::default(), Word::default());
185 /// let mutations = smt.compute_mutations(vec![pair]);
186 /// assert_eq!(mutations.root(), *EmptySubtreeRoots::entry(SMT_DEPTH, 0));
187 /// smt.apply_mutations(mutations);
188 /// assert_eq!(smt.root(), *EmptySubtreeRoots::entry(SMT_DEPTH, 0));
189 /// ```
190 pub fn compute_mutations(
191 &self,
192 kv_pairs: impl IntoIterator<Item = (RpoDigest, Word)>,
193 ) -> MutationSet<SMT_DEPTH, RpoDigest, Word> {
194 <Self as SparseMerkleTree<SMT_DEPTH>>::compute_mutations(self, kv_pairs)
195 }
196
197 /// Apply the prospective mutations computed with [`Smt::compute_mutations()`] to this tree.
198 ///
199 /// # Errors
200 /// If `mutations` was computed on a tree with a different root than this one, returns
201 /// [`MerkleError::ConflictingRoots`] with a two-item [`Vec`]. The first item is the root hash
202 /// the `mutations` were computed against, and the second item is the actual current root of
203 /// this tree.
204 pub fn apply_mutations(
205 &mut self,
206 mutations: MutationSet<SMT_DEPTH, RpoDigest, Word>,
207 ) -> Result<(), MerkleError> {
208 <Self as SparseMerkleTree<SMT_DEPTH>>::apply_mutations(self, mutations)
209 }
210
211 // HELPERS
212 // --------------------------------------------------------------------------------------------
213
214 /// Inserts `value` at leaf index pointed to by `key`. `value` is guaranteed to not be the empty
215 /// value, such that this is indeed an insertion.
216 fn perform_insert(&mut self, key: RpoDigest, value: Word) -> Option<Word> {
217 debug_assert_ne!(value, Self::EMPTY_VALUE);
218
219 let leaf_index: LeafIndex<SMT_DEPTH> = Self::key_to_leaf_index(&key);
220
221 match self.leaves.get_mut(&leaf_index.value()) {
222 Some(leaf) => leaf.insert(key, value),
223 None => {
224 self.leaves.insert(leaf_index.value(), SmtLeaf::Single((key, value)));
225
226 None
227 },
228 }
229 }
230
231 /// Removes key-value pair at leaf index pointed to by `key` if it exists.
232 fn perform_remove(&mut self, key: RpoDigest) -> Option<Word> {
233 let leaf_index: LeafIndex<SMT_DEPTH> = Self::key_to_leaf_index(&key);
234
235 if let Some(leaf) = self.leaves.get_mut(&leaf_index.value()) {
236 let (old_value, is_empty) = leaf.remove(key);
237 if is_empty {
238 self.leaves.remove(&leaf_index.value());
239 }
240 old_value
241 } else {
242 // there's nothing stored at the leaf; nothing to update
243 None
244 }
245 }
246}
247
248impl SparseMerkleTree<SMT_DEPTH> for Smt {
249 type Key = RpoDigest;
250 type Value = Word;
251 type Leaf = SmtLeaf;
252 type Opening = SmtProof;
253
254 const EMPTY_VALUE: Self::Value = EMPTY_WORD;
255
256 fn root(&self) -> RpoDigest {
257 self.root
258 }
259
260 fn set_root(&mut self, root: RpoDigest) {
261 self.root = root;
262 }
263
264 fn get_inner_node(&self, index: NodeIndex) -> InnerNode {
265 self.inner_nodes
266 .get(&index)
267 .cloned()
268 .unwrap_or_else(|| EmptySubtreeRoots::get_inner_node(SMT_DEPTH, index.depth()))
269 }
270
271 fn insert_inner_node(&mut self, index: NodeIndex, inner_node: InnerNode) {
272 self.inner_nodes.insert(index, inner_node);
273 }
274
275 fn remove_inner_node(&mut self, index: NodeIndex) {
276 let _ = self.inner_nodes.remove(&index);
277 }
278
279 fn insert_value(&mut self, key: Self::Key, value: Self::Value) -> Option<Self::Value> {
280 // inserting an `EMPTY_VALUE` is equivalent to removing any value associated with `key`
281 if value != Self::EMPTY_VALUE {
282 self.perform_insert(key, value)
283 } else {
284 self.perform_remove(key)
285 }
286 }
287
288 fn get_value(&self, key: &Self::Key) -> Self::Value {
289 let leaf_pos = LeafIndex::<SMT_DEPTH>::from(*key).value();
290
291 match self.leaves.get(&leaf_pos) {
292 Some(leaf) => leaf.get_value(key).unwrap_or_default(),
293 None => EMPTY_WORD,
294 }
295 }
296
297 fn get_leaf(&self, key: &RpoDigest) -> Self::Leaf {
298 let leaf_pos = LeafIndex::<SMT_DEPTH>::from(*key).value();
299
300 match self.leaves.get(&leaf_pos) {
301 Some(leaf) => leaf.clone(),
302 None => SmtLeaf::new_empty(key.into()),
303 }
304 }
305
306 fn hash_leaf(leaf: &Self::Leaf) -> RpoDigest {
307 leaf.hash()
308 }
309
310 fn construct_prospective_leaf(
311 &self,
312 mut existing_leaf: SmtLeaf,
313 key: &RpoDigest,
314 value: &Word,
315 ) -> SmtLeaf {
316 debug_assert_eq!(existing_leaf.index(), Self::key_to_leaf_index(key));
317
318 match existing_leaf {
319 SmtLeaf::Empty(_) => SmtLeaf::new_single(*key, *value),
320 _ => {
321 if *value != EMPTY_WORD {
322 existing_leaf.insert(*key, *value);
323 } else {
324 existing_leaf.remove(*key);
325 }
326
327 existing_leaf
328 },
329 }
330 }
331
332 fn key_to_leaf_index(key: &RpoDigest) -> LeafIndex<SMT_DEPTH> {
333 let most_significant_felt = key[3];
334 LeafIndex::new_max_depth(most_significant_felt.as_int())
335 }
336
337 fn path_and_leaf_to_opening(path: MerklePath, leaf: SmtLeaf) -> SmtProof {
338 SmtProof::new_unchecked(path, leaf)
339 }
340}
341
342impl Default for Smt {
343 fn default() -> Self {
344 Self::new()
345 }
346}
347
348// CONVERSIONS
349// ================================================================================================
350
351impl From<Word> for LeafIndex<SMT_DEPTH> {
352 fn from(value: Word) -> Self {
353 // We use the most significant `Felt` of a `Word` as the leaf index.
354 Self::new_max_depth(value[3].as_int())
355 }
356}
357
358impl From<RpoDigest> for LeafIndex<SMT_DEPTH> {
359 fn from(value: RpoDigest) -> Self {
360 Word::from(value).into()
361 }
362}
363
364impl From<&RpoDigest> for LeafIndex<SMT_DEPTH> {
365 fn from(value: &RpoDigest) -> Self {
366 Word::from(value).into()
367 }
368}
369
370// SERIALIZATION
371// ================================================================================================
372
373impl Serializable for Smt {
374 fn write_into<W: ByteWriter>(&self, target: &mut W) {
375 // Write the number of filled leaves for this Smt
376 target.write_usize(self.entries().count());
377
378 // Write each (key, value) pair
379 for (key, value) in self.entries() {
380 target.write(key);
381 target.write(value);
382 }
383 }
384}
385
386impl Deserializable for Smt {
387 fn read_from<R: ByteReader>(source: &mut R) -> Result<Self, DeserializationError> {
388 // Read the number of filled leaves for this Smt
389 let num_filled_leaves = source.read_usize()?;
390 let mut entries = Vec::with_capacity(num_filled_leaves);
391
392 for _ in 0..num_filled_leaves {
393 let key = source.read()?;
394 let value = source.read()?;
395 entries.push((key, value));
396 }
397
398 Self::with_entries(entries)
399 .map_err(|err| DeserializationError::InvalidValue(err.to_string()))
400 }
401}
402
403#[test]
404fn test_smt_serialization_deserialization() {
405 // Smt for default types (empty map)
406 let smt_default = Smt::default();
407 let bytes = smt_default.to_bytes();
408 assert_eq!(smt_default, Smt::read_from_bytes(&bytes).unwrap());
409
410 // Smt with values
411 let smt_leaves_2: [(RpoDigest, Word); 2] = [
412 (
413 RpoDigest::new([Felt::new(101), Felt::new(102), Felt::new(103), Felt::new(104)]),
414 [Felt::new(1_u64), Felt::new(2_u64), Felt::new(3_u64), Felt::new(4_u64)],
415 ),
416 (
417 RpoDigest::new([Felt::new(105), Felt::new(106), Felt::new(107), Felt::new(108)]),
418 [Felt::new(5_u64), Felt::new(6_u64), Felt::new(7_u64), Felt::new(8_u64)],
419 ),
420 ];
421 let smt = Smt::with_entries(smt_leaves_2).unwrap();
422
423 let bytes = smt.to_bytes();
424 assert_eq!(smt, Smt::read_from_bytes(&bytes).unwrap());
425}