Crate merkletree
source ·Expand description
light Merkle Tree implementation.
Merkle tree (MT) implemented as a full (power of 2) arity tree allocated as a vec
of statically sized hashes to give hashes more locality (although disk based backings
are supported, as a partial tree disk based backings). MT is specialized
to the extent of arity, hashing algorithm and hash item. [Hashable
] trait is
compatible to the std::hash::Hasher
and supports custom hash algorithms.
Implementation does not depend on any external crypto libraries, and tries
to be as performant as possible (CPU support only; GPU hashing currently unsupported).
This tree implementation uses encoding scheme as in Certificate Transparency by default. Encoding scheme for leafs and nodes can be overridden though. RFC 6962:
MTH({d(0)}) = ALG(0x00 || d(0)).
For n > 1, let k be the largest power of two smaller than n (i.e.,
k < n <= 2k). The Merkle tree Hash of an n-element list D[n] is then
defined recursively as
MTH(D[n]) = ALG(0x01 || MTH(D[0:k]) || MTH(D[k:n])),
§Implementation choices
Main idea is the whole code must obtain specialization at compile time with minimum allocations calls, hashes must be of fixed size arrays known at compile time, hash algorithm must be a trait and must not depend on any external cryptographic libraries and the lib itself must somehow mimic std Rust api.
Standard way in Rust is to hash objects with a std::hash::Hasher
, and mainly
that is the reason behind the choice of the abstractions:
Object : Hashable<H> -> Hasher + Algorithm <- Merkle Tree
Custom [merkle::hash::Hashable
] trait allows implementations differ
from [std::collection
] related hashes, different implementations for
different hashing algorithms / schemas and conforms object-safety trait rules.
[Algorithm
] complements [Hasher
] to be reusable and follows the idea
that the result hash is a mapping of the data stream.
[Algorithm.hash
] had to change its signature to be &mut self
(&self
) because
most of the cryptographic digest algorithms breaks current state on finalization
into unusable. ring
libra tho contains interfaces incompatible to
start-update-finish-reset
lifecycle. It requires either cloning()
its state
on finalization, or Cell
-ing via unsafe.
Turning back to having [Algorithm.write(&mut self, &[u8])
] instead of
write(T)
allows to relax [Algorithm
] trait [Hasher
] constraint, even tho
works together well still.
§Interface
- build_tree (items) -> tree
- get_root -> hash
- gen_proof -> proof
- validate_proof (proof, leaf, root) -> bool
§Examples
[test_common.rs
]: custom hash example xor128, misc shared utils
[test_xor128.rs
]: most comprehensive tests for library features
[proof.rs
]: contains impl and tests for proofs across pow2 arity trees
Modules§
- Hash infrastructure for items in Merkle tree. Hash infrastructure for items in Merkle Tree.
- Merkle tree abstractions, implementation and algorithms.
- Merkle tree inclusion proof.
- Store implementations.