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pre-compute empty trees

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This commit is contained in:
David Rusu 2024-12-05 23:47:52 +04:00
parent 11556f07e8
commit bd1f928e00
2 changed files with 41 additions and 29 deletions
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3
emmarin/cl/cl/Cargo.toml
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@ -12,4 +12,5 @@ rand = "0.8.5"
rand_core = "0.6.0"
hex = "0.4.3"
curve25519-dalek = {version = "4.1", features = ["serde", "digest", "rand_core"]}
sha2 = "0.10"
sha2 = "0.10"
lazy_static = "1.5.0"

67
emmarin/cl/cl/src/zone_layer/sparse_merkle_tree.rs
View File

@ -1,6 +1,26 @@
use std::collections::BTreeSet;
use crate::cl::merkle;
use lazy_static::lazy_static;
/// absence of element is marked with all 0's
static ABSENT: [u8; 32] = [0u8; 32];
/// presence of element is marked with all 1's
static PRESENT: [u8; 32] = [255u8; 32];
lazy_static! {
// the roots of empty merkle trees of diffent heights
// i.e. all leafs are ABSENT
static ref EMPTY_ROOTS: [[u8; 32]; 256] = {
let mut roots = [ABSENT; 256];
for h in 1..256 {
roots[h] = merkle::node(roots[h - 1], roots[h - 1]);
}
roots
};
}
pub fn sparse_root(elems: &BTreeSet<[u8; 32]>) -> [u8; 32] {
sparse_root_rec(0, elems)
@ -12,7 +32,7 @@ fn sparse_root_rec(prefix: u8, elems: &BTreeSet<[u8; 32]>) -> [u8; 32] {
}
if prefix == 255 {
assert_eq!(elems.len(), 1);
return merkle::leaf(&[255u8; 32]); // presence of element is marked with all 1's
return PRESENT;
}
// partition the elements
let (left, right): (BTreeSet<_>, BTreeSet<_>) = elems.iter().partition(|e| !bit(prefix, **e));
@ -58,11 +78,7 @@ pub fn sparse_path(elem: [u8; 32], elems: &BTreeSet<[u8; 32]>) -> Vec<merkle::Pa
}
fn empty_tree_root(height: u8) -> [u8; 32] {
let mut root = merkle::leaf(&[0u8; 32]);
for _ in 0..height {
root = merkle::node(root, root);
}
root
EMPTY_ROOTS[height as usize]
}
fn bit(idx: u8, elem: [u8; 32]) -> bool {
@ -84,16 +100,13 @@ mod tests {
fn test_sparse_path() {
let elems = BTreeSet::from_iter(std::iter::repeat_with(random_hash).take(10));
let one = merkle::leaf(&[255u8; 32]);
let zero = merkle::leaf(&[0u8; 32]);
let root = sparse_root(&elems);
// membership proofs
for e in elems.iter() {
let path = sparse_path(*e, &elems);
assert_eq!(path.len(), 255);
assert_eq!(merkle::path_root(one, &path), root);
assert_eq!(merkle::path_root(PRESENT, &path), root);
}
// non-membership proofs
@ -102,7 +115,7 @@ mod tests {
let path = sparse_path(elem, &elems);
assert!(!elems.contains(&elem));
assert_eq!(path.len(), 255);
assert_eq!(merkle::path_root(zero, &path), root);
assert_eq!(merkle::path_root(ABSENT, &path), root);
}
}
@ -112,8 +125,7 @@ mod tests {
let path = sparse_path([0u8; 32], &BTreeSet::new());
let zero = merkle::leaf(&[0u8; 32]);
assert_eq!(merkle::path_root(zero, &path), root);
assert_eq!(merkle::path_root(ABSENT, &path), root);
for (h, node) in path.into_iter().enumerate() {
match node {
@ -134,7 +146,7 @@ mod tests {
// / \ 0 subtree
// / \ 0 subtree
// 1 0
let mut expected_root = merkle::leaf(&[255u8; 32]);
let mut expected_root = PRESENT;
for h in 0..=254 {
expected_root = merkle::node(expected_root, empty_tree_root(h))
}
@ -152,7 +164,7 @@ mod tests {
// 0 /\
// 0 /\
// 0 1
let mut expected_root = merkle::leaf(&[255u8; 32]);
let mut expected_root = PRESENT;
for h in 0..=254 {
expected_root = merkle::node(empty_tree_root(h), expected_root)
}
@ -183,7 +195,7 @@ mod tests {
// 0 ...
// \
// 1
let mut expected_root = merkle::leaf(&[255u8; 32]);
let mut expected_root = PRESENT;
for h in 0..=253 {
expected_root = merkle::node(empty_tree_root(h), expected_root)
}
@ -210,7 +222,7 @@ mod tests {
// /\0
// 0 1
let mut expected_root = merkle::leaf(&[255u8; 32]);
let mut expected_root = PRESENT;
for h in 0..=254 {
if h % 2 == 0 {
expected_root = merkle::node(empty_tree_root(h), expected_root)
@ -232,12 +244,12 @@ mod tests {
// /\0 0 /\
// 1 0 0 1
let mut left_root = merkle::leaf(&[255u8; 32]);
let mut left_root = PRESENT;
for h in 0..=253 {
left_root = merkle::node(left_root, empty_tree_root(h))
}
let mut right_root = merkle::leaf(&[255u8; 32]);
let mut right_root = PRESENT;
for h in 0..=253 {
right_root = merkle::node(empty_tree_root(h), right_root)
}
@ -249,32 +261,31 @@ mod tests {
#[test]
fn test_bit() {
for i in 0..=255 {
assert_eq!(bit(i, [0u8; 32]), false, "{}", i)
assert!(!bit(i, [0u8; 32]))
}
for i in 0..=255 {
assert_eq!(bit(i, [255u8; 32]), true, "{}", i)
assert!(bit(i, [255u8; 32]))
}
for i in 0..=255 {
assert_eq!(bit(i, [85u8; 32]), i % 2 == 0, "{}", i)
assert_eq!(bit(i, [85u8; 32]), i % 2 == 0)
}
}
#[test]
fn test_empty_tree_root() {
let zero = merkle::leaf(&[0u8; 32]);
assert_eq!(empty_tree_root(0), zero);
assert_eq!(empty_tree_root(0), ABSENT);
assert_eq!(empty_tree_root(1), merkle::node(zero, zero));
assert_eq!(empty_tree_root(1), merkle::node(ABSENT, ABSENT));
assert_eq!(
empty_tree_root(2),
merkle::node(merkle::node(zero, zero), merkle::node(zero, zero)),
merkle::node(merkle::node(ABSENT, ABSENT), merkle::node(ABSENT, ABSENT)),
);
assert_eq!(
empty_tree_root(3),
merkle::node(
merkle::node(merkle::node(zero, zero), merkle::node(zero, zero)),
merkle::node(merkle::node(zero, zero), merkle::node(zero, zero)),
merkle::node(merkle::node(ABSENT, ABSENT), merkle::node(ABSENT, ABSENT)),
merkle::node(merkle::node(ABSENT, ABSENT), merkle::node(ABSENT, ABSENT)),
)
);
}