miden-crypto/src/merkle/path_set.rs
src/merkle/path_set.rsRaw
1use super::{BTreeMap, MerkleError, MerklePath, NodeIndex, Rpo256, ValuePath, Vec};
2use crate::{hash::rpo::RpoDigest, Word};
3
4// MERKLE PATH SET
5// ================================================================================================
6
7/// A set of Merkle paths.
8#[derive(Debug, Clone, PartialEq, Eq)]
9pub struct MerklePathSet {
10 root: RpoDigest,
11 total_depth: u8,
12 paths: BTreeMap<u64, MerklePath>,
13}
14
15impl MerklePathSet {
16 // CONSTRUCTOR
17 // --------------------------------------------------------------------------------------------
18
19 /// Returns an empty MerklePathSet.
20 pub fn new(depth: u8) -> Self {
21 let root = RpoDigest::default();
22 let paths = BTreeMap::new();
23
24 Self {
25 root,
26 total_depth: depth,
27 paths,
28 }
29 }
30
31 /// Appends the provided paths iterator into the set.
32 ///
33 /// Analogous to `[Self::add_path]`.
34 pub fn with_paths<I>(self, paths: I) -> Result<Self, MerkleError>
35 where
36 I: IntoIterator<Item = (u64, RpoDigest, MerklePath)>,
37 {
38 paths.into_iter().try_fold(self, |mut set, (index, value, path)| {
39 set.add_path(index, value, path)?;
40 Ok(set)
41 })
42 }
43
44 // PUBLIC ACCESSORS
45 // --------------------------------------------------------------------------------------------
46
47 /// Returns the root to which all paths in this set resolve.
48 pub const fn root(&self) -> RpoDigest {
49 self.root
50 }
51
52 /// Returns the depth of the Merkle tree implied by the paths stored in this set.
53 ///
54 /// Merkle tree of depth 1 has two leaves, depth 2 has four leaves etc.
55 pub const fn depth(&self) -> u8 {
56 self.total_depth
57 }
58
59 /// Returns a node at the specified index.
60 ///
61 /// # Errors
62 /// Returns an error if:
63 /// * The specified index is not valid for the depth of structure.
64 /// * Requested node does not exist in the set.
65 pub fn get_node(&self, index: NodeIndex) -> Result<RpoDigest, MerkleError> {
66 if index.depth() != self.total_depth {
67 return Err(MerkleError::InvalidDepth {
68 expected: self.total_depth,
69 provided: index.depth(),
70 });
71 }
72
73 let parity = index.value() & 1;
74 let path_key = index.value() - parity;
75 self.paths
76 .get(&path_key)
77 .ok_or(MerkleError::NodeNotInSet(index))
78 .map(|path| path[parity as usize])
79 }
80
81 /// Returns a leaf at the specified index.
82 ///
83 /// # Errors
84 /// * The specified index is not valid for the depth of the structure.
85 /// * Leaf with the requested path does not exist in the set.
86 pub fn get_leaf(&self, index: u64) -> Result<Word, MerkleError> {
87 let index = NodeIndex::new(self.depth(), index)?;
88 Ok(self.get_node(index)?.into())
89 }
90
91 /// Returns a Merkle path to the node at the specified index. The node itself is
92 /// not included in the path.
93 ///
94 /// # Errors
95 /// Returns an error if:
96 /// * The specified index is not valid for the depth of structure.
97 /// * Node of the requested path does not exist in the set.
98 pub fn get_path(&self, index: NodeIndex) -> Result<MerklePath, MerkleError> {
99 if index.depth() != self.total_depth {
100 return Err(MerkleError::InvalidDepth {
101 expected: self.total_depth,
102 provided: index.depth(),
103 });
104 }
105
106 let parity = index.value() & 1;
107 let path_key = index.value() - parity;
108 let mut path =
109 self.paths.get(&path_key).cloned().ok_or(MerkleError::NodeNotInSet(index))?;
110 path.remove(parity as usize);
111 Ok(path)
112 }
113
114 /// Returns all paths in this path set together with their indexes.
115 pub fn to_paths(&self) -> Vec<(u64, ValuePath)> {
116 let mut result = Vec::with_capacity(self.paths.len() * 2);
117
118 for (&index, path) in self.paths.iter() {
119 // push path for the even index into the result
120 let path1 = ValuePath {
121 value: path[0],
122 path: MerklePath::new(path[1..].to_vec()),
123 };
124 result.push((index, path1));
125
126 // push path for the odd index into the result
127 let mut path2 = path.clone();
128 let leaf2 = path2.remove(1);
129 let path2 = ValuePath {
130 value: leaf2,
131 path: path2,
132 };
133 result.push((index + 1, path2));
134 }
135
136 result
137 }
138
139 // STATE MUTATORS
140 // --------------------------------------------------------------------------------------------
141
142 /// Adds the specified Merkle path to this [MerklePathSet]. The `index` and `value` parameters
143 /// specify the leaf node at which the path starts.
144 ///
145 /// # Errors
146 /// Returns an error if:
147 /// - The specified index is is not valid in the context of this Merkle path set (i.e., the
148 /// index implies a greater depth than is specified for this set).
149 /// - The specified path is not consistent with other paths in the set (i.e., resolves to a
150 /// different root).
151 pub fn add_path(
152 &mut self,
153 index_value: u64,
154 value: RpoDigest,
155 mut path: MerklePath,
156 ) -> Result<(), MerkleError> {
157 let mut index = NodeIndex::new(path.len() as u8, index_value)?;
158 if index.depth() != self.total_depth {
159 return Err(MerkleError::InvalidDepth {
160 expected: self.total_depth,
161 provided: index.depth(),
162 });
163 }
164
165 // update the current path
166 let parity = index_value & 1;
167 path.insert(parity as usize, value);
168
169 // traverse to the root, updating the nodes
170 let root: RpoDigest = Rpo256::merge(&[path[0], path[1]]);
171 let root = path.iter().skip(2).copied().fold(root, |root, hash| {
172 index.move_up();
173 Rpo256::merge(&index.build_node(root, hash))
174 });
175
176 // if the path set is empty (the root is all ZEROs), set the root to the root of the added
177 // path; otherwise, the root of the added path must be identical to the current root
178 if self.root == RpoDigest::default() {
179 self.root = root;
180 } else if self.root != root {
181 return Err(MerkleError::ConflictingRoots([self.root, root].to_vec()));
182 }
183
184 // finish updating the path
185 let path_key = index_value - parity;
186 self.paths.insert(path_key, path);
187 Ok(())
188 }
189
190 /// Replaces the leaf at the specified index with the provided value.
191 ///
192 /// # Errors
193 /// Returns an error if:
194 /// * Requested node does not exist in the set.
195 pub fn update_leaf(
196 &mut self,
197 base_index_value: u64,
198 value: RpoDigest,
199 ) -> Result<(), MerkleError> {
200 let mut index = NodeIndex::new(self.depth(), base_index_value)?;
201 let parity = index.value() & 1;
202 let path_key = index.value() - parity;
203 let path = match self.paths.get_mut(&path_key) {
204 Some(path) => path,
205 None => return Err(MerkleError::NodeNotInSet(index)),
206 };
207
208 // Fill old_hashes vector -----------------------------------------------------------------
209 let mut current_index = index;
210 let mut old_hashes = Vec::with_capacity(path.len().saturating_sub(2));
211 let mut root: RpoDigest = Rpo256::merge(&[path[0], path[1]]);
212 for hash in path.iter().skip(2).copied() {
213 old_hashes.push(root);
214 current_index.move_up();
215 let input = current_index.build_node(hash, root);
216 root = Rpo256::merge(&input);
217 }
218
219 // Fill new_hashes vector -----------------------------------------------------------------
220 path[index.is_value_odd() as usize] = value;
221
222 let mut new_hashes = Vec::with_capacity(path.len().saturating_sub(2));
223 let mut new_root: RpoDigest = Rpo256::merge(&[path[0], path[1]]);
224 for path_hash in path.iter().skip(2).copied() {
225 new_hashes.push(new_root);
226 index.move_up();
227 let input = current_index.build_node(path_hash, new_root);
228 new_root = Rpo256::merge(&input);
229 }
230
231 self.root = new_root;
232
233 // update paths ---------------------------------------------------------------------------
234 for path in self.paths.values_mut() {
235 for i in (0..old_hashes.len()).rev() {
236 if path[i + 2] == old_hashes[i] {
237 path[i + 2] = new_hashes[i];
238 break;
239 }
240 }
241 }
242
243 Ok(())
244 }
245}
246
247// TESTS
248// ================================================================================================
249
250#[cfg(test)]
251mod tests {
252 use super::*;
253 use crate::merkle::int_to_node;
254
255 #[test]
256 fn get_root() {
257 let leaf0 = int_to_node(0);
258 let leaf1 = int_to_node(1);
259 let leaf2 = int_to_node(2);
260 let leaf3 = int_to_node(3);
261
262 let parent0 = calculate_parent_hash(leaf0, 0, leaf1);
263 let parent1 = calculate_parent_hash(leaf2, 2, leaf3);
264
265 let root_exp = calculate_parent_hash(parent0, 0, parent1);
266
267 let set = super::MerklePathSet::new(2)
268 .with_paths([(0, leaf0, vec![leaf1, parent1].into())])
269 .unwrap();
270
271 assert_eq!(set.root(), root_exp);
272 }
273
274 #[test]
275 fn add_and_get_path() {
276 let path_6 = vec![int_to_node(7), int_to_node(45), int_to_node(123)];
277 let hash_6 = int_to_node(6);
278 let index = 6_u64;
279 let depth = 3_u8;
280 let set = super::MerklePathSet::new(depth)
281 .with_paths([(index, hash_6, path_6.clone().into())])
282 .unwrap();
283 let stored_path_6 = set.get_path(NodeIndex::make(depth, index)).unwrap();
284
285 assert_eq!(path_6, *stored_path_6);
286 }
287
288 #[test]
289 fn get_node() {
290 let path_6 = vec![int_to_node(7), int_to_node(45), int_to_node(123)];
291 let hash_6 = int_to_node(6);
292 let index = 6_u64;
293 let depth = 3_u8;
294 let set = MerklePathSet::new(depth).with_paths([(index, hash_6, path_6.into())]).unwrap();
295
296 assert_eq!(int_to_node(6u64), set.get_node(NodeIndex::make(depth, index)).unwrap());
297 }
298
299 #[test]
300 fn update_leaf() {
301 let hash_4 = int_to_node(4);
302 let hash_5 = int_to_node(5);
303 let hash_6 = int_to_node(6);
304 let hash_7 = int_to_node(7);
305 let hash_45 = calculate_parent_hash(hash_4, 12u64, hash_5);
306 let hash_67 = calculate_parent_hash(hash_6, 14u64, hash_7);
307
308 let hash_0123 = int_to_node(123);
309
310 let path_6 = vec![hash_7, hash_45, hash_0123];
311 let path_5 = vec![hash_4, hash_67, hash_0123];
312 let path_4 = vec![hash_5, hash_67, hash_0123];
313
314 let index_6 = 6_u64;
315 let index_5 = 5_u64;
316 let index_4 = 4_u64;
317 let depth = 3_u8;
318 let mut set = MerklePathSet::new(depth)
319 .with_paths([
320 (index_6, hash_6, path_6.into()),
321 (index_5, hash_5, path_5.into()),
322 (index_4, hash_4, path_4.into()),
323 ])
324 .unwrap();
325
326 let new_hash_6 = int_to_node(100);
327 let new_hash_5 = int_to_node(55);
328
329 set.update_leaf(index_6, new_hash_6).unwrap();
330 let new_path_4 = set.get_path(NodeIndex::make(depth, index_4)).unwrap();
331 let new_hash_67 = calculate_parent_hash(new_hash_6, 14_u64, hash_7);
332 assert_eq!(new_hash_67, new_path_4[1]);
333
334 set.update_leaf(index_5, new_hash_5).unwrap();
335 let new_path_4 = set.get_path(NodeIndex::make(depth, index_4)).unwrap();
336 let new_path_6 = set.get_path(NodeIndex::make(depth, index_6)).unwrap();
337 let new_hash_45 = calculate_parent_hash(new_hash_5, 13_u64, hash_4);
338 assert_eq!(new_hash_45, new_path_6[1]);
339 assert_eq!(new_hash_5, new_path_4[0]);
340 }
341
342 #[test]
343 fn depth_3_is_correct() {
344 let a = int_to_node(1);
345 let b = int_to_node(2);
346 let c = int_to_node(3);
347 let d = int_to_node(4);
348 let e = int_to_node(5);
349 let f = int_to_node(6);
350 let g = int_to_node(7);
351 let h = int_to_node(8);
352
353 let i = Rpo256::merge(&[a, b]);
354 let j = Rpo256::merge(&[c, d]);
355 let k = Rpo256::merge(&[e, f]);
356 let l = Rpo256::merge(&[g, h]);
357
358 let m = Rpo256::merge(&[i, j]);
359 let n = Rpo256::merge(&[k, l]);
360
361 let root = Rpo256::merge(&[m.into(), n.into()]);
362
363 let mut set = MerklePathSet::new(3);
364
365 let value = b;
366 let index = 1;
367 let path = MerklePath::new([a, j, n].to_vec());
368 set.add_path(index, value, path.clone()).unwrap();
369 assert_eq!(*value, set.get_leaf(index).unwrap());
370 assert_eq!(RpoDigest::from(root), set.root());
371
372 let value = e;
373 let index = 4;
374 let path = MerklePath::new([f.into(), l.into(), m.into()].to_vec());
375 set.add_path(index, value, path.clone()).unwrap();
376 assert_eq!(*value, set.get_leaf(index).unwrap());
377 assert_eq!(RpoDigest::from(root), set.root());
378
379 let value = a;
380 let index = 0;
381 let path = MerklePath::new([b.into(), j.into(), n.into()].to_vec());
382 set.add_path(index, value, path.clone()).unwrap();
383 assert_eq!(*value, set.get_leaf(index).unwrap());
384 assert_eq!(RpoDigest::from(root), set.root());
385
386 let value = h;
387 let index = 7;
388 let path = MerklePath::new([g.into(), k.into(), m.into()].to_vec());
389 set.add_path(index, value, path.clone()).unwrap();
390 assert_eq!(*value, set.get_leaf(index).unwrap());
391 assert_eq!(RpoDigest::from(root), set.root());
392 }
393
394 // HELPER FUNCTIONS
395 // --------------------------------------------------------------------------------------------
396
397 const fn is_even(pos: u64) -> bool {
398 pos & 1 == 0
399 }
400
401 /// Calculates the hash of the parent node by two sibling ones
402 /// - node — current node
403 /// - node_pos — position of the current node
404 /// - sibling — neighboring vertex in the tree
405 fn calculate_parent_hash(node: RpoDigest, node_pos: u64, sibling: RpoDigest) -> RpoDigest {
406 if is_even(node_pos) {
407 Rpo256::merge(&[node, sibling])
408 } else {
409 Rpo256::merge(&[sibling, node])
410 }
411 }
412}