Trait ex3_merkle::Hasher

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pub trait Hasher: Clone {
    type Hash: Copy + PartialEq + Into<Vec<u8>> + TryFrom<Vec<u8>>;

    // Required method
    fn hash(data: &[u8]) -> Self::Hash;

    // Provided methods
    fn concat_and_hash(
        left: &Self::Hash,
        right: Option<&Self::Hash>
    ) -> Self::Hash { ... }
    fn hash_size() -> usize { ... }
}
Expand description

Hasher is a trait used to provide a hashing algorithm for the library.

Example

This example shows how to implement the sha256 algorithm

use rs_merkle::{Hasher};
use sha2::{Sha256, Digest, digest::FixedOutput};

#[derive(Clone)]
pub struct Sha256Algorithm {}

impl Hasher for Sha256Algorithm {
    type Hash = [u8; 32];

    fn hash(data: &[u8]) -> [u8; 32] {
        let mut hasher = Sha256::new();

        hasher.update(data);
        <[u8; 32]>::from(hasher.finalize_fixed())
    }
}

Required Associated Types§

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type Hash: Copy + PartialEq + Into<Vec<u8>> + TryFrom<Vec<u8>>

This type is used as a hash type in the library. It is recommended to use fixed size u8 array as a hash type. For example, for sha256 the type would be [u8; 32], representing 32 bytes, which is the size of the sha256 digest. Also, fixed sized arrays of u8 by default satisfy all trait bounds required by this type.

Trait bounds

Copy is required as the hash needs to be copied to be concatenated/propagated when constructing nodes. PartialEq is required to compare equality when verifying proof Into<Vec<u8>> is required to be able to serialize proof TryFrom<Vec<u8>> is required to parse hashes from a serialized proof

Required Methods§

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fn hash(data: &[u8]) -> Self::Hash

This associated function takes a slice of bytes and returns a hash of it. Used by concat_and_hash function to build a tree from concatenated hashes

Provided Methods§

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fn concat_and_hash(left: &Self::Hash, right: Option<&Self::Hash>) -> Self::Hash

Used by MerkleTree and PartialTree when calculating the root. The provided default implementation propagates the left node if it doesn’t have a sibling. The left node should always be present. The right node is optional.

For the tree to be compatible with different types of proofs this function needs to be overridden. For example, in Bitcoin implementation, if the left node doesn’t have a sibling it is concatenated to itself and then hashed instead of just being propagated to the next level.

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fn hash_size() -> usize

Returns the byte size of Self::Hash. Default implementation returns mem::size_of::<Self::Hash>(). Usually doesn’t need to be overridden. Used internally by MerkleProof to parse hashes from a serialized proof.

Implementors§