Wrong hasher for of DefaultBinaryTree

[vmx]

Description

The DefaultBinaryTree is defined as BinaryMerkleTree<DefaultTreeHasher>, while DefaultTreeHasher = PoseidonHasher:

rust-fil-proofs/filecoin-proofs/src/constants.rs

Line 144 in aecc1ee

pub type DefaultBinaryTree = BinaryMerkleTree<DefaultTreeHasher>;

Though the DefaultBinaryTree is also used at code paths which use SHA2 hashing, e.g.:

rust-fil-proofs/filecoin-proofs/src/api/seal.rs

Line 133 in aecc1ee

let base_tree_size = get_base_tree_size::<DefaultBinaryTree>(porep_config.sector_size)?;

.

The current code works, because the code paths the DefaultBinaryTree is used on, it only cares about the arity and the size of the hashes, which is the same for SHA2 and Poseidon. Though for correctness and clarity, the correct hasher for DefaultBinaryTree should be used.

Acceptance criteria

The correct hashers are uses for the corresponding trees.

Risks + pitfalls

Sometimes the Poseidon hasher might be needed. It needs thorough review whether changing the DefaultBinaryTree to SHA2 is enough, or whether some new type needs to be introduced.

Where to begin

Look at all occurrences of DefaultBinaryTree and check if SHA2 or Poseidon hashing should be used.

[vmx]

I've assigned this issue to @storojs72 as you are familiar with the merkle trees and it's a good way to dig deeper into how they are used.

[storojs72]

Yes, I agree. We indeed have some confusing places in the codebase (where it is not obvious whether Poseidon or Sha256 hasher should be really used) that require clarification