CryptoConcurrency: (Almost) Consensusless Asset Transfer with Shared Accounts

TL;DR

CryptoConcurrency introduces a novel asset transfer protocol that enables parallel, consensus-free processing of concurrent transactions on shared accounts, enhancing decentralization and efficiency in blockchain systems.

Contribution

It presents a new protocol allowing concurrent asset transfers without global consensus, using per-account consensus only when overspending risks occur.

Findings

Enables parallel processing of transfers without consensus when safe.

Allows each account to have its own consensus mechanism.

Reduces reliance on centralized consensus for asset transfers.

Abstract

A typical blockchain protocol uses consensus to make sure that mutually mistrusting users agree on the order in which their operations on shared data are executed. However, it is known that asset transfer systems, by far the most popular application of blockchains, can be implemented without consensus. Assuming that no account can be accessed concurrently and every account belongs to a single owner, one can efficiently implement an asset transfer system in a purely asynchronous, consensus-free manner. It has also been shown that implementing asset transfer with shared accounts is impossible without consensus. In this paper, we propose CryptoConcurrency, an asset transfer protocol that allows concurrent accesses to be processed in parallel, without involving consensus, whenever possible. More precisely, if concurrent transfer operations on a given account do not lead to overspending, i.e. can all be applied without the account balance going below zero, they proceed in parallel. Otherwise, the account's owners may have to access an external consensus object. Notably, we avoid relying on a central, universally-trusted, consensus mechanism and allow each account to use its own consensus implementation, which only the owners of this account trust. This provides greater decentralization and flexibility.