From 2573f050a33935c966e4e76df743bc25f7beb644 Mon Sep 17 00:00:00 2001 From: Qyriad Date: Thu, 22 Aug 2024 19:00:36 -0600 Subject: [PATCH] feat(smt): implement root-checked insertion This commit implements SparseMerkleTree::insert_ensure_root(), a version of SparseMerkleTree::insert() that prevents modification of the tree if the insert turns out to not result in the correct tree root (i.e., the transaction is not valid). This is an initial step towards issue 222. As a logical next step, generalizing this to validation of inserting multiple values at once will directly enable removing Merkle tree clones in miden-node InnerState::apply_block(). For further work, as we generalize pre-validation for mutations we will want a separate type to represent an arbitrary set of prospective mutations on the Merkle tree and their validity, like the `ChangeSet` type suggested in the issue. --- CHANGELOG.md | 1 + src/merkle/smt/full/mod.rs | 44 +++++++++++---- src/merkle/smt/full/tests.rs | 102 ++++++++++++++++++++++++++++------ src/merkle/smt/mod.rs | 105 ++++++++++++++++++++++++++++++++--- src/merkle/smt/simple/mod.rs | 27 ++++++++- 5 files changed, 242 insertions(+), 37 deletions(-) diff --git a/CHANGELOG.md b/CHANGELOG.md index 76c65a7..7d1dd39 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -3,6 +3,7 @@ - [BREAKING]: renamed `Mmr::open()` into `Mmr::open_at()` and `Mmr::peaks()` into `Mmr::peaks_at()` (#234). - Added `Mmr::open()` and `Mmr::peaks()` which rely on `Mmr::open_at()` and `Mmr::peaks()` respectively (#234). - Standardised CI and Makefile across Miden repos (#323). +- Added `Smt::insert_ensure_root()` for root-validated insertion (#327) ## 0.10.0 (2024-08-06) diff --git a/src/merkle/smt/full/mod.rs b/src/merkle/smt/full/mod.rs index 205a443..60b7bd2 100644 --- a/src/merkle/smt/full/mod.rs +++ b/src/merkle/smt/full/mod.rs @@ -167,6 +167,24 @@ impl Smt { >::insert(self, key, value) } + /// Like [`Self::insert()`], but only performs the insert if the new tree's root + /// hash would be equal to the hash given in `expected_root`. + /// + /// # Errors + /// Returns [`MerkleError::ConflictingRoots`] with a two-item [Vec] if the new root of the tree + /// is different from the expected root. The first item of the vector is the expected root, + /// and the second is the actual root. + /// + /// No mutations are performed if the roots do not match. + pub fn insert_ensure_root( + &mut self, + key: RpoDigest, + value: Word, + expected_root: RpoDigest, + ) -> Result { + >::insert_ensure_root(self, key, value, expected_root) + } + // HELPERS // -------------------------------------------------------------------------------------------- @@ -274,21 +292,23 @@ impl SparseMerkleTree for Smt { } } - fn hash_prospective_leaf(&self, key: &RpoDigest, value: &Word) -> RpoDigest { - // Future work could avoid cloning the leaf by mirroring some of the insertion logic and - // hashing without an intermediate leaf, but cloning is only expensive for multi-leaves, - // which should be really rare. - let leaf_index: LeafIndex = Self::key_to_leaf_index(key); - match self.leaves.get(&leaf_index.value()) { - None => SmtLeaf::new_single(*key, *value).hash(), - Some(existing_leaf) => { - let mut new_leaf = existing_leaf.clone(); + fn get_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 { - new_leaf.insert(*key, *value); + existing_leaf.insert(*key, *value); } else { - new_leaf.remove(*key); + existing_leaf.remove(*key); } - new_leaf.hash() + existing_leaf }, } } diff --git a/src/merkle/smt/full/tests.rs b/src/merkle/smt/full/tests.rs index 1ee7f9d..2c4e8c8 100644 --- a/src/merkle/smt/full/tests.rs +++ b/src/merkle/smt/full/tests.rs @@ -2,7 +2,7 @@ use alloc::vec::Vec; use super::{Felt, LeafIndex, NodeIndex, Rpo256, RpoDigest, Smt, SmtLeaf, EMPTY_WORD, SMT_DEPTH}; use crate::{ - merkle::{smt::SparseMerkleTree, EmptySubtreeRoots, MerkleStore}, + merkle::{smt::SparseMerkleTree, EmptySubtreeRoots, MerkleError, MerkleStore}, utils::{Deserializable, Serializable}, Word, ONE, WORD_SIZE, }; @@ -259,24 +259,30 @@ fn test_smt_removal() { } #[test] -fn test_prospective_hash() { +fn test_checked_insertion() { + use MerkleError::ConflictingRoots; + let mut smt = Smt::default(); + let smt_empty = smt.clone(); let raw = 0b_01101001_01101100_00011111_11111111_10010110_10010011_11100000_00000000_u64; let key_1: RpoDigest = RpoDigest::from([ONE, ONE, ONE, Felt::new(raw)]); let key_2: RpoDigest = RpoDigest::from([2_u32.into(), 2_u32.into(), 2_u32.into(), Felt::new(raw)]); + // Sort key_3 before key_1, to test non-append insertion. let key_3: RpoDigest = - RpoDigest::from([3_u32.into(), 3_u32.into(), 3_u32.into(), Felt::new(raw)]); + RpoDigest::from([0_u32.into(), 0_u32.into(), 0_u32.into(), Felt::new(raw)]); let value_1 = [ONE; WORD_SIZE]; let value_2 = [2_u32.into(); WORD_SIZE]; let value_3: [Felt; 4] = [3_u32.into(); WORD_SIZE]; + let root_empty = smt.root(); + // insert key-value 1 - { - let prospective = smt.hash_prospective_leaf(&key_1, &value_1); + let root_1 = { + let prospective = smt.get_prospective_leaf(smt.get_leaf(&key_1), &key_1, &value_1).hash(); let old_value_1 = smt.insert(key_1, value_1); assert_eq!(old_value_1, EMPTY_WORD); @@ -284,11 +290,30 @@ fn test_prospective_hash() { assert_eq!(smt.get_leaf(&key_1), SmtLeaf::Single((key_1, value_1))); + smt.root() + }; + + { + // Trying to insert something else into key_1 with the existing root should fail, and + // should not modify the tree at all. + let smt_before = smt.clone(); + assert!(matches!( + smt.insert_ensure_root(key_1, value_2, root_1), + Err(ConflictingRoots(_)), + )); + assert_eq!(smt, smt_before); + + // And inserting an empty word should bring us back to where we were. + assert_eq!(smt.insert_ensure_root(key_1, EMPTY_WORD, root_empty), Ok(value_1)); + assert_eq!(smt, smt_empty); + + smt.insert_ensure_root(key_1, value_1, root_1).unwrap(); + assert_eq!(smt, smt_before); } // insert key-value 2 - { - let prospective = smt.hash_prospective_leaf(&key_2, &value_2); + let root_2 = { + let prospective = smt.get_prospective_leaf(smt.get_leaf(&key_2), &key_2, &value_2).hash(); let old_value_2 = smt.insert(key_2, value_2); assert_eq!(old_value_2, EMPTY_WORD); @@ -298,11 +323,26 @@ fn test_prospective_hash() { smt.get_leaf(&key_2), SmtLeaf::Multiple(vec![(key_1, value_1), (key_2, value_2)]) ); + + smt.root() + }; + + { + let smt_before = smt.clone(); + assert!(matches!( + smt.insert_ensure_root(key_2, value_1, root_2), + Err(ConflictingRoots(_)), + )); + assert_eq!(smt, smt_before); + + assert_eq!(smt.insert_ensure_root(key_2, EMPTY_WORD, root_1), Ok(value_2)); + smt.insert_ensure_root(key_2, value_2, root_2).unwrap(); + assert_eq!(smt, smt_before); } // insert key-value 3 - { - let prospective = smt.hash_prospective_leaf(&key_3, &value_3); + let root_3 = { + let prospective = smt.get_prospective_leaf(smt.get_leaf(&key_3), &key_3, &value_3).hash(); let old_value_3 = smt.insert(key_3, value_3); assert_eq!(old_value_3, EMPTY_WORD); @@ -310,41 +350,71 @@ fn test_prospective_hash() { assert_eq!( smt.get_leaf(&key_3), - SmtLeaf::Multiple(vec![(key_1, value_1), (key_2, value_2), (key_3, value_3)]) + SmtLeaf::Multiple(vec![(key_3, value_3), (key_1, value_1), (key_2, value_2)]) ); + + smt.root() + }; + + { + let smt_before = smt.clone(); + assert!(matches!( + smt.insert_ensure_root(key_3, value_1, root_3), + Err(ConflictingRoots(_)), + )); + assert_eq!(smt, smt_before); + + assert_eq!(smt.insert_ensure_root(key_3, EMPTY_WORD, root_2), Ok(value_3)); + smt.insert_ensure_root(key_3, value_3, root_3).unwrap(); + assert_eq!(smt, smt_before); } // remove key 3 { let old_hash = smt.get_leaf(&key_3).hash(); - let old_value_3 = smt.insert(key_3, EMPTY_WORD); + let old_value_3 = smt.insert_ensure_root(key_3, EMPTY_WORD, root_2).unwrap(); assert_eq!(old_value_3, value_3); - assert_eq!(old_hash, smt.hash_prospective_leaf(&key_3, &old_value_3)); + assert_eq!( + old_hash, + smt.get_prospective_leaf(smt.get_leaf(&key_3), &key_3, &old_value_3).hash() + ); assert_eq!( smt.get_leaf(&key_3), SmtLeaf::Multiple(vec![(key_1, value_1), (key_2, value_2)]) ); + + assert_eq!(smt.root(), root_2); } // remove key 2 { let old_hash = smt.get_leaf(&key_2).hash(); - let old_value_2 = smt.insert(key_2, EMPTY_WORD); + let old_value_2 = smt.insert_ensure_root(key_2, EMPTY_WORD, root_1).unwrap(); assert_eq!(old_value_2, value_2); - assert_eq!(old_hash, smt.hash_prospective_leaf(&key_2, &old_value_2)); + assert_eq!( + old_hash, + smt.get_prospective_leaf(smt.get_leaf(&key_2), &key_2, &old_value_2).hash() + ); assert_eq!(smt.get_leaf(&key_2), SmtLeaf::Single((key_1, value_1))); + + assert_eq!(smt.root(), root_1); } // remove key 1 { let old_hash = smt.get_leaf(&key_1).hash(); - let old_value_1 = smt.insert(key_1, EMPTY_WORD); + let old_value_1 = smt.insert_ensure_root(key_1, EMPTY_WORD, root_empty).unwrap(); assert_eq!(old_value_1, value_1); - assert_eq!(old_hash, smt.hash_prospective_leaf(&key_1, &old_value_1)); + assert_eq!( + old_hash, + smt.get_prospective_leaf(smt.get_leaf(&key_1), &key_1, &old_value_1).hash() + ); assert_eq!(smt.get_leaf(&key_1), SmtLeaf::new_empty(key_1.into())); + + assert_eq!(smt.root(), root_empty); } } diff --git a/src/merkle/smt/mod.rs b/src/merkle/smt/mod.rs index 962c893..a36c314 100644 --- a/src/merkle/smt/mod.rs +++ b/src/merkle/smt/mod.rs @@ -110,6 +110,92 @@ pub(crate) trait SparseMerkleTree { old_value } + /// Like [`Self::insert()`], but only performs the insert if the new tree's root hash would + /// be equal to the hash given in `expected_root`. + /// + /// # Errors + /// Returns [`MerkleError::ConflictingRoots`] with a two-item [Vec] if the new root of the tree + /// is different from the expected root. The first item of the vector is the expected root, + /// and the second is the actual root. + /// + /// No mutations are performed if the roots do not match. + fn insert_ensure_root( + &mut self, + key: Self::Key, + value: Self::Value, + expected_root: RpoDigest, + ) -> Result { + let old_value = self.get_value(&key); + // if the old value and new value are the same, there is nothing to update + if value == old_value { + return Ok(value); + } + + // Compute the nodes we'll need to make and remove. + let mut removals: Vec = Vec::with_capacity(DEPTH as usize); + let mut additions: Vec<(NodeIndex, InnerNode)> = Vec::with_capacity(DEPTH as usize); + + let mut node_index = { + let leaf_index: LeafIndex = Self::key_to_leaf_index(&key); + NodeIndex::from(leaf_index) + }; + + let mut new_child_hash = + Self::hash_leaf(&self.get_prospective_leaf(self.get_leaf(&key), &key, &value)); + for node_depth in (0..node_index.depth()).rev() { + let is_right = node_index.is_value_odd(); + node_index.move_up(); + + let old_node = self.get_inner_node(node_index); + let new_node = if is_right { + InnerNode { + left: old_node.left, + right: new_child_hash, + } + } else { + InnerNode { + left: new_child_hash, + right: old_node.right, + } + }; + + // The next iteration will operate on this node's new hash. + new_child_hash = new_node.hash(); + + let &equivalent_empty_hash = EmptySubtreeRoots::entry(DEPTH, node_depth); + if new_child_hash == equivalent_empty_hash { + // If a subtree is empty, we can remove the inner node, since it's equal to the + // default value. + removals.push(node_index); + } else { + additions.push((node_index, new_node)); + } + } + + // Once we're at depth 0, the last node we made is the new root. + let new_root = new_child_hash; + + if expected_root != new_root { + return Err(MerkleError::ConflictingRoots(vec![expected_root, new_root])); + } + + // Actual mutations start here. + + self.insert_value(key, value); + + for index in removals.drain(..) { + self.remove_inner_node(index); + } + + for (index, new_node) in additions.drain(..) { + self.insert_inner_node(index, new_node); + } + + self.set_root(new_root); + + Ok(old_value) + } + /// Recomputes the branch nodes (including the root) from `index` all the way to the root. /// `node_hash_at_index` is the hash of the node stored at index. fn recompute_nodes_from_index_to_root( @@ -175,14 +261,19 @@ pub(crate) trait SparseMerkleTree { #[allow(dead_code)] fn is_leaf_empty(leaf: &Self::Leaf) -> bool; - /// Returns the hash of a leaf if the leaf WERE inserted into the tree, - /// without performing any insertion or other mutation. + /// Returns what `existing_leaf` would look like if `key` and `value` WERE inserted into the + /// tree, without mutating the tree itself. /// - /// Note: calling this function after actually performing an insert with the same arguments - /// will *not* return the same result, as inserting multiple times with the same key mutates - /// the leaf each time. - #[cfg_attr(not(test), allow(dead_code))] - fn hash_prospective_leaf(&self, key: &Self::Key, value: &Self::Value) -> RpoDigest; + /// `existing_leaf` must have the same index as the key, or the result will be meaningless. To + /// get a prospective leaf based on the current state of the tree, use `self.get_leaf(key)` as + /// the argument for `existing_leaf`. The return value from this function can be chained back + /// into this function as the first argument to continue making prospective changes. + fn get_prospective_leaf( + &self, + existing_leaf: Self::Leaf, + key: &Self::Key, + value: &Self::Value, + ) -> Self::Leaf; /// Maps a key to a leaf index fn key_to_leaf_index(key: &Self::Key) -> LeafIndex; diff --git a/src/merkle/smt/simple/mod.rs b/src/merkle/smt/simple/mod.rs index bcc4099..80bc2f1 100644 --- a/src/merkle/smt/simple/mod.rs +++ b/src/merkle/smt/simple/mod.rs @@ -188,6 +188,24 @@ impl SimpleSmt { >::insert(self, key, value) } + /// Like [`Self::insert()`], but only performs the insert if the new tree's root hash would + /// be equal to the hash given in `expected_root`. + /// + /// # Errors + /// Returns [`MerkleError::ConflictingRoots`] with a two-item [alloc::vec::Vec] if the new + /// root of the tree is different from the expected root. The first item of the vector is + /// the expected root, and the second is the actual root. + /// + /// No mutations are performed if the roots do not match. + pub fn insert_ensure_root( + &mut self, + key: LeafIndex, + value: Word, + expected_root: RpoDigest, + ) -> Result { + >::insert_ensure_root(self, key, value, expected_root) + } + /// Inserts a subtree at the specified index. The depth at which the subtree is inserted is /// computed as `DEPTH - SUBTREE_DEPTH`. /// @@ -310,8 +328,13 @@ impl SparseMerkleTree for SimpleSmt { *leaf == Self::EMPTY_VALUE } - fn hash_prospective_leaf(&self, _key: &LeafIndex, value: &Word) -> RpoDigest { - Self::hash_leaf(value) + fn get_prospective_leaf( + &self, + _existing_leaf: Word, + _key: &LeafIndex, + value: &Word, + ) -> Word { + *value } fn key_to_leaf_index(key: &LeafIndex) -> LeafIndex {