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Monero: expose merkle root function #629

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Monero: expose merkle root function #629

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980c5f0
Monero: expose merkel root function
Boog900 Nov 15, 2024
05cda97
review fixes
Boog900 Nov 15, 2024
e6fdef6
change `merkle_root` return to `Option`
Boog900 Nov 15, 2024
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11 changes: 8 additions & 3 deletions networks/monero/src/block.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -121,8 +121,13 @@ impl Block {
/// use the [`Block::hash`] function.
pub fn serialize_pow_hash(&self) -> Vec<u8> {
let mut blob = self.header.serialize();
blob.extend_from_slice(&merkle_root(self.miner_transaction.hash(), &self.transactions));
write_varint(&(1 + u64::try_from(self.transactions.len()).unwrap()), &mut blob).unwrap();

let mut transactions = Vec::with_capacity(self.transactions.len() + 1);
transactions.push(self.miner_transaction.hash());
transactions.extend_from_slice(&self.transactions);

blob.extend_from_slice(&merkle_root(&transactions));
write_varint(&(1 + self.transactions.len()), &mut blob).unwrap();
blob
}

Expand All @@ -132,7 +137,7 @@ impl Block {
// Monero pre-appends a VarInt of the block-to-hash'ss length before getting the block hash,
// but doesn't do this when getting the proof of work hash :)
let mut hashing_blob = Vec::with_capacity(9 + hashable.len());
write_varint(&u64::try_from(hashable.len()).unwrap(), &mut hashing_blob).unwrap();
write_varint(&hashable.len(), &mut hashing_blob).unwrap();
hashing_blob.append(&mut hashable);

let hash = keccak256(hashing_blob);
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3 changes: 2 additions & 1 deletion networks/monero/src/lib.rs
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Expand Up @@ -7,7 +7,8 @@ pub use monero_io as io;
pub use monero_generators as generators;
pub use monero_primitives as primitives;

mod merkle;
/// Merkel tree functionality.
pub mod merkle;

/// Ring Signature structs and functionality.
pub mod ring_signatures;
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11 changes: 5 additions & 6 deletions networks/monero/src/merkle.rs
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Expand Up @@ -2,14 +2,13 @@ use std_shims::vec::Vec;

use crate::primitives::keccak256;

pub(crate) fn merkle_root(root: [u8; 32], leafs: &[[u8; 32]]) -> [u8; 32] {
/// Calculates the merkel root of the given tree. Equivalent to `tree_hash` in monero-core.
pub fn merkle_root(leafs: &[[u8; 32]]) -> [u8; 32] {
match leafs.len() {
0 => root,
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We used to handle no leaves being passed. Now no hashes falls through to the n-leaves case. Is that correct?

I doubt it as our n-leaf code pads to the nearest power of 2 which is assumed to be 4 as we assumed exceptional handling for 0/1/2.

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Ah yeah it will panic, I guess the best thing to do would be to explicitly panic, tree_hash doesn't allow a 0 length input: https://github.com/monero-project/monero/blob/893916ad091a92e765ce3241b94e706ad012b62a/src/crypto/tree-hash.c#L62

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@kayabaNerve kayabaNerve Nov 15, 2024 •
edited
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That would've been so easy for me to check if there was a link to tree_hash present :p

*There wasn't such a link prior, I don't legitimately want to hold this against you.

I'd vote we keep the existing explicit argument (potentially renamed from root to first_leaf?) making this unreachable, or return an Option. We can document the panic but I'd consider that a downgrade. Even the Option would be but it isn't such a downgrade I wouldn't agree to it if you believe avoiding these allocations so worthwhile.

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I'll change it to return an option, I don't really like having the first leaf as a separate arg.

1 => keccak256([root, leafs[0]].concat()),
1 => leafs[0],
2 => keccak256([leafs[0], leafs[1]].concat()),
_ => {
let mut hashes = Vec::with_capacity(1 + leafs.len());
hashes.push(root);
hashes.extend(leafs);
let mut hashes = leafs.to_vec();

// Monero preprocess this so the length is a power of 2
let mut high_pow_2 = 4; // 4 is the lowest value this can be
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