sheth

sheth [ ˈshēth ] is an execution environment (EE) for Ethereum 2.0 that facilitates the movement of ether within a shard and provides mechanisms to move ether between a shard and the beacon chain.

Quick Start

First, setup your environment:

rustup target install wasm32-unknown-unknown
cargo install chisel
make setup

Then simulate execution using Scout:

make scout

Or run on your local architecture (useful for tracking down bugs):

make test

Recommended Reading

The design space for EEs is broad and builds on many different Ethereum 2.0 related concepts. If you're lost, here are a few places to get started:

• Phase 2 Wiki
• Phase 2 Proposal
• Eth EE Proposal

Ping me @lightclients for any other questions / concerns.

Motivation

• Understanding the developer experience regarding EEs could influence design decisions of the protocol and EE runtime.
• Efficiently authenticating and updating merkle multi-proofs is critical to the success of stateless execution environments.
• In order to develop strong tooling for EE development, it's important to determine a lower bound for execution time and binary size to target.
• Provide a framework on which others can develop and experiment.

Architecture

At a high level, sheth provides a single state transition function:

pub fn main(pre_state: &[u8; 32], data: &[u8]) -> [u8; 32];

The main function essentially takes in the latest merkle root of the state as pre_state and some amount of data. It deserializes the data into the transactions that will be executed and the merkle multi-proof which is used authenticate the transactions. Due to some of the semantics of WebAssembly, it isn't quite this simple (see the FFI interface) -- but the general idea remains intact.

sheth's design is heavily influenced by Vitalik's sample EE in his phase 2 proposal.

State

The state can be thought of abstractly as an array [Account, 2**256], where an account's index in the array is equal to Sha256(account.pubkey). This is far too large to fit into memory all at once, so operations are done on specific elements within a merkle multi-proof.

The sparse merkle tree for sheth's state can be roughly visualized as follows:

FL = first leaf node = 2**256
LL = last leaf node = 2**257 - 1
        
              +---------- 1 ----------+             
             /                         \
        +-- 2 --+                   +-- 3 --+       
       /         \                 /         \
     ...         ...             ...         ...   
    /   \       /   \           /   \       /   \
  FL+0 FL+1   FL+2 FL+3  ...  LL-3 LL-2   LL-1 LL-0 

Each leaf node is the root of the corresponding account. An account's merkle tree structure is as follows:

              +--- account ---+
             /                 \
      pubkey_root           sub_root    
        /     \              /    \     
  pk[0..32] pk[32..48]    nonce  value

Merkle Multi-Proof

A merkle multi-proof is a data structure which stores multiple branches proving various items within the state. For a formal definition, see the specification.

Example

Imagine a merkle tree of this shape (e.g. an account):

     1
   /   \
  2     3
 / \   / \
4   5 6   7

In order to prove 6 is included in the root at 1, the nodes [2, 6, 7] would be needed since 1 and 3 can be calculated from that set.

     1
   /   \
 [2]    3
 / \   / \
4   5[6] [7]

Roadmap

• Support intra-shard transfers
• Consume beacon chain withdrawal receipts
• Allow shard ether to be deposited to the beacon chain
• Validate transaction signature against BLS pubkey
• Verify transaction nonce against account
• Implement merge functionality for multiple packages
• Minimize binary size
• Minimize execution time
• Minimize multi-proof size

License

Licensed under Apache License, Version 2.0 (http://www.apache.org/licenses/LICENSE-2.0)