Crate eml 

EML — Epoch Merkle Log

A single RFC 9162 append-only Merkle tree supporting dynamic sets of hash algorithms over a shared topology. Algorithms activate and deactivate between appends. A new algorithm’s view of pre-activation positions consists of deterministic null constants, enabling O(log n) algorithm addition without retroactive computation.

See docs/models/epoch-merkle-log.md for the formal model.

Architecture

EML is algorithm-agnostic. Callers provide hash implementations via the Hasher trait. Leaf storage is decoupled via the Storage trait. The crate has zero runtime dependencies.

Proofs

EML generates standard RFC 9162 inclusion and consistency proofs per algorithm. Proofs verify against the standard verify_inclusion and verify_consistency functions — no modified verifier is needed.

Specification vs. implementation. The formal model (§11) defines project(S, a) as an O(n) specification oracle — the conceptual per-algorithm leaf sequence that establishes correctness via equational laws. The implementation does not materialize this sequence. Proof generation instead uses subtree_root (§11c), which resolves sibling hashes via O(1) stored-node lookups, achieving O(log n) proof generation. The correctness bridge (§12) proves these produce identical output.

Usage

use eml::{Log, Hasher, MemoryStorage};

// Implement Hasher for your algorithm, then:
let mut log = Log::new(MemoryStorage::new());
log.add_algorithm(0, my_hasher);     // algorithm 0 active from genesis
log.append(b"first entry");
let root = log.root(0).unwrap();

Structs

AlgorithmInfo

Per-algorithm metadata snapshot (Definition 13).

ConsistencyProof

Consistency proof — proves a tree of old_size is a prefix of new_size.

ElidedInclusionProof

An inclusion proof with null subtree siblings elided.

InclusionProof

Inclusion proof — proves a leaf at index exists in a tree of tree_size.

Log

An Epoch Merkle Log.

MemoryStorage

In-memory leaf and node storage backed by collections.

MemoryStorageError

Error type for MemoryStorage operations.

NullTable

Precomputed null subtree constants for a single algorithm.

Enums

Error

Errors that can occur during EML operations.

Traits

Hasher

Hash operations required by the EML tree.

Storage

Backend for persisting and retrieving raw leaf payloads and sealed internal node hashes.

Functions

elide_inclusion_proof

Elide null subtree siblings from a full inclusion proof.

rehydrate_inclusion_proof

Rehydrate an elided inclusion proof by synthesizing null subtree hashes.

verify_consistency

Verify a consistency proof (RFC 9162 §2.1.4.2).

verify_inclusion

Verify an inclusion proof (RFC 9162 §2.1.3.2).

Type Aliases

AlgorithmMetas

Reconstructed metadata for registered algorithms: a list of (alg_id, epochs) pairs.

Epochs

Epoch metadata for a registered algorithm: a sequence of half-open [start, end) intervals.

Result

Convenience alias.