Algorithm for Cross-shard Cross-EE Atomic User-level ETH Transfer in Ethereum

TL;DR

This paper presents a novel method for atomic cross-shard ETH transfers in Ethereum's sharded architecture, ensuring atomicity despite Byzantine failures without requiring locks, by leveraging netted-balance channels and handling various failure scenarios.

Contribution

It introduces a cross-shard transfer protocol that guarantees atomicity in Ethereum's sharded environment using netted-balance channels, without locks or proposer constraints.

Findings

Ensures atomicity even with Byzantine block proposers.

Does not require locks or specific transaction ordering.

Provides bounds on inter-shard state read sizes.

Abstract

Sharding is a way to address scalability problem in blockchain technologies. Ethereum, a prominent blockchain technology, has included sharding in its roadmap to increase its throughput. The plan is also to include multiple execution environments. We address the problem of atomic cross shard value transfer in the presence of multiple execution environments. We leverage on the proposed Ethereum architecture, more specificially on Beacon chain and crosslinks, and propose a solution on top of the netted-balance approach that was proposed for EE-level atomic \eth transfers. We split a cross-shard transfer into two transactions: a debit and a credit. First, the debit transaction is processed at the source shard. The corresponding credit transaction is processed at the destination shard in a subsequent block. We use {\em netted} shard states as channels to communicate pending credits and pending reverts. We discuss various scenarios of debit failures and credit failures, and show our approach ensures atomicity even in the presence of a Byzantine Block proposer. The benefits of our approach are that we do not use any locks nor impose any constraints on the Block Proposer to select specific transactions. However we inherit the limitation of an expensive operation from the netted-balance approach of querying partial states from all other shards. We also show a bound on the size of such inter-shard state reads.