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Offline Merkle Computation

Compute Merkle roots locally without an indexer. Useful for testing, verification, and analytics.

Functions​

empty_root_hex()​

Returns the root of an empty Merkle tree (all leaves zero). This is the initial root stored on-chain during init-contract.

use r14_sdk::merkle::empty_root_hex;

let root = empty_root_hex();
assert_eq!(root.len(), 64); // 32 bytes, no 0x prefix

The empty root is computed by iterating hash2(0, 0) for MERKLE_DEPTH (20) levels.

compute_root_from_leaves()​

Compute the Merkle root for a given set of leaf commitments. Produces the same result as the indexer's SparseMerkleTree::root() for the same leaf set.

use r14_sdk::merkle::compute_root_from_leaves;
use r14_sdk::wallet::hex_to_fr;

let cm1 = hex_to_fr("0x1a2b3c...")?;
let cm2 = hex_to_fr("0x4d5e6f...")?;

let root = compute_root_from_leaves(&[cm1, cm2]);
println!("root: {}", root); // 64-char hex, no 0x prefix

Properties​

  • Order matters: compute_root_from_leaves(&[a, b]) differs from compute_root_from_leaves(&[b, a]). Leaves are ordered by insertion index.
  • Deterministic: Same inputs always produce the same root.
  • Hash function: Poseidon hash2 at every level.
  • Tree depth: 20 levels, supporting up to 1,048,576 (2^20) leaves.
  • Empty subtrees: Unpopulated subtrees use precomputed zero hashes (hash2(zero_i, zero_i) per level).

CLI​

# Empty tree root
r14 compute-root

# Root with specific commitments (no 0x prefix)
r14 compute-root 1a2b3c4d5e6f... 7a8b9c0d1e2f...

With JSON output:

r14 compute-root --json 1a2b3c4d5e6f...
{
  "root": "a1b2c3d4e5f6..."
}

Use Cases​

Testing: Verify that your local Merkle tree matches the indexer's without making network calls.

use r14_sdk::merkle::{empty_root_hex, compute_root_from_leaves};
use r14_sdk::{Note, commitment, owner_hash, SecretKey};
use r14_sdk::wallet::crypto_rng;

let mut rng = crypto_rng();
let sk = SecretKey::random(&mut rng);
let owner = owner_hash(&sk);

let note = Note::new(1000, 1, owner.0, &mut rng);
let cm = commitment(&note);

let root_before = empty_root_hex();
let root_after = compute_root_from_leaves(&[cm]);
assert_ne!(root_before, root_after);

Verification: Confirm that a deposit correctly changed the root.

// Before deposit: root_before = compute_root_from_leaves(&existing_leaves)
// After deposit:  root_after  = compute_root_from_leaves(&[existing_leaves..., new_cm])

Analytics: Compute roots for arbitrary subsets of commitments offline for auditing or reconciliation purposes.