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 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 let leaf_pos = LeafIndex::<SMT_DEPTH>::from(*key).value();
125
126 match self.leaves.get(&leaf_pos) {
127 Some(leaf) => leaf.get_value(key).unwrap_or_default(),
128 None => EMPTY_WORD,
129 }
130 }
131
132 /// Returns an opening of the leaf associated with `key`. Conceptually, an opening is a Merkle
133 /// path to the leaf, as well as the leaf itself.
134 pub fn open(&self, key: &RpoDigest) -> SmtProof {
135 <Self as SparseMerkleTree<SMT_DEPTH>>::open(self, key)
136 }
137
138 // ITERATORS
139 // --------------------------------------------------------------------------------------------
140
141 /// Returns an iterator over the leaves of this [Smt].
142 pub fn leaves(&self) -> impl Iterator<Item = (LeafIndex<SMT_DEPTH>, &SmtLeaf)> {
143 self.leaves
144 .iter()
145 .map(|(leaf_index, leaf)| (LeafIndex::new_max_depth(*leaf_index), leaf))
146 }
147
148 /// Returns an iterator over the key-value pairs of this [Smt].
149 pub fn entries(&self) -> impl Iterator<Item = &(RpoDigest, Word)> {
150 self.leaves().flat_map(|(_, leaf)| leaf.entries())
151 }
152
153 /// Returns an iterator over the inner nodes of this [Smt].
154 pub fn inner_nodes(&self) -> impl Iterator<Item = InnerNodeInfo> + '_ {
155 self.inner_nodes.values().map(|e| InnerNodeInfo {
156 value: e.hash(),
157 left: e.left,
158 right: e.right,
159 })
160 }
161
162 // STATE MUTATORS
163 // --------------------------------------------------------------------------------------------
164
165 /// Inserts a value at the specified key, returning the previous value associated with that key.
166 /// Recall that by definition, any key that hasn't been updated is associated with
167 /// [`Self::EMPTY_VALUE`].
168 ///
169 /// This also recomputes all hashes between the leaf (associated with the key) and the root,
170 /// updating the root itself.
171 pub fn insert(&mut self, key: RpoDigest, value: Word) -> Word {
172 <Self as SparseMerkleTree<SMT_DEPTH>>::insert(self, key, value)
173 }
174
175 // HELPERS
176 // --------------------------------------------------------------------------------------------
177
178 /// Inserts `value` at leaf index pointed to by `key`. `value` is guaranteed to not be the empty
179 /// value, such that this is indeed an insertion.
180 fn perform_insert(&mut self, key: RpoDigest, value: Word) -> Option<Word> {
181 debug_assert_ne!(value, Self::EMPTY_VALUE);
182
183 let leaf_index: LeafIndex<SMT_DEPTH> = Self::key_to_leaf_index(&key);
184
185 match self.leaves.get_mut(&leaf_index.value()) {
186 Some(leaf) => leaf.insert(key, value),
187 None => {
188 self.leaves.insert(leaf_index.value(), SmtLeaf::Single((key, value)));
189
190 None
191 },
192 }
193 }
194
195 /// Removes key-value pair at leaf index pointed to by `key` if it exists.
196 fn perform_remove(&mut self, key: RpoDigest) -> Option<Word> {
197 let leaf_index: LeafIndex<SMT_DEPTH> = Self::key_to_leaf_index(&key);
198
199 if let Some(leaf) = self.leaves.get_mut(&leaf_index.value()) {
200 let (old_value, is_empty) = leaf.remove(key);
201 if is_empty {
202 self.leaves.remove(&leaf_index.value());
203 }
204 old_value
205 } else {
206 // there's nothing stored at the leaf; nothing to update
207 None
208 }
209 }
210}
211
212impl SparseMerkleTree<SMT_DEPTH> for Smt {
213 type Key = RpoDigest;
214 type Value = Word;
215 type Leaf = SmtLeaf;
216 type Opening = SmtProof;
217
218 const EMPTY_VALUE: Self::Value = EMPTY_WORD;
219
220 fn root(&self) -> RpoDigest {
221 self.root
222 }
223
224 fn set_root(&mut self, root: RpoDigest) {
225 self.root = root;
226 }
227
228 fn get_inner_node(&self, index: NodeIndex) -> InnerNode {
229 self.inner_nodes.get(&index).cloned().unwrap_or_else(|| {
230 let node = EmptySubtreeRoots::entry(SMT_DEPTH, index.depth() + 1);
231
232 InnerNode { left: *node, right: *node }
233 })
234 }
235
236 fn insert_inner_node(&mut self, index: NodeIndex, inner_node: InnerNode) {
237 self.inner_nodes.insert(index, inner_node);
238 }
239
240 fn remove_inner_node(&mut self, index: NodeIndex) {
241 let _ = self.inner_nodes.remove(&index);
242 }
243
244 fn insert_value(&mut self, key: Self::Key, value: Self::Value) -> Option<Self::Value> {
245 // inserting an `EMPTY_VALUE` is equivalent to removing any value associated with `key`
246 if value != Self::EMPTY_VALUE {
247 self.perform_insert(key, value)
248 } else {
249 self.perform_remove(key)
250 }
251 }
252
253 fn get_leaf(&self, key: &RpoDigest) -> Self::Leaf {
254 let leaf_pos = LeafIndex::<SMT_DEPTH>::from(*key).value();
255
256 match self.leaves.get(&leaf_pos) {
257 Some(leaf) => leaf.clone(),
258 None => SmtLeaf::new_empty(key.into()),
259 }
260 }
261
262 fn hash_leaf(leaf: &Self::Leaf) -> RpoDigest {
263 leaf.hash()
264 }
265
266 fn key_to_leaf_index(key: &RpoDigest) -> LeafIndex<SMT_DEPTH> {
267 let most_significant_felt = key[3];
268 LeafIndex::new_max_depth(most_significant_felt.as_int())
269 }
270
271 fn path_and_leaf_to_opening(path: MerklePath, leaf: SmtLeaf) -> SmtProof {
272 SmtProof::new_unchecked(path, leaf)
273 }
274}
275
276impl Default for Smt {
277 fn default() -> Self {
278 Self::new()
279 }
280}
281
282// CONVERSIONS
283// ================================================================================================
284
285impl From<Word> for LeafIndex<SMT_DEPTH> {
286 fn from(value: Word) -> Self {
287 // We use the most significant `Felt` of a `Word` as the leaf index.
288 Self::new_max_depth(value[3].as_int())
289 }
290}
291
292impl From<RpoDigest> for LeafIndex<SMT_DEPTH> {
293 fn from(value: RpoDigest) -> Self {
294 Word::from(value).into()
295 }
296}
297
298impl From<&RpoDigest> for LeafIndex<SMT_DEPTH> {
299 fn from(value: &RpoDigest) -> Self {
300 Word::from(value).into()
301 }
302}
303
304// SERIALIZATION
305// ================================================================================================
306
307impl Serializable for Smt {
308 fn write_into<W: ByteWriter>(&self, target: &mut W) {
309 // Write the number of filled leaves for this Smt
310 target.write_usize(self.entries().count());
311
312 // Write each (key, value) pair
313 for (key, value) in self.entries() {
314 target.write(key);
315 target.write(value);
316 }
317 }
318}
319
320impl Deserializable for Smt {
321 fn read_from<R: ByteReader>(source: &mut R) -> Result<Self, DeserializationError> {
322 // Read the number of filled leaves for this Smt
323 let num_filled_leaves = source.read_usize()?;
324 let mut entries = Vec::with_capacity(num_filled_leaves);
325
326 for _ in 0..num_filled_leaves {
327 let key = source.read()?;
328 let value = source.read()?;
329 entries.push((key, value));
330 }
331
332 Self::with_entries(entries)
333 .map_err(|err| DeserializationError::InvalidValue(err.to_string()))
334 }
335}
336
337#[test]
338fn test_smt_serialization_deserialization() {
339 // Smt for default types (empty map)
340 let smt_default = Smt::default();
341 let bytes = smt_default.to_bytes();
342 assert_eq!(smt_default, Smt::read_from_bytes(&bytes).unwrap());
343
344 // Smt with values
345 let smt_leaves_2: [(RpoDigest, Word); 2] = [
346 (
347 RpoDigest::new([Felt::new(101), Felt::new(102), Felt::new(103), Felt::new(104)]),
348 [Felt::new(1_u64), Felt::new(2_u64), Felt::new(3_u64), Felt::new(4_u64)],
349 ),
350 (
351 RpoDigest::new([Felt::new(105), Felt::new(106), Felt::new(107), Felt::new(108)]),
352 [Felt::new(5_u64), Felt::new(6_u64), Felt::new(7_u64), Felt::new(8_u64)],
353 ),
354 ];
355 let smt = Smt::with_entries(smt_leaves_2).unwrap();
356
357 let bytes = smt.to_bytes();
358 assert_eq!(smt, Smt::read_from_bytes(&bytes).unwrap());
359}