Consensus on Demand
This work addresses the scalability and functionality limitations in decentralized digital currencies, offering a hybrid approach that balances efficiency with consensus capabilities, though it is incremental in combining existing broadcast and consensus methods.
The paper tackles the problem of digital money systems that avoid consensus but cannot handle conflicting transactions or support smart contracts, by introducing a protocol that performs consensus only when necessary, achieving optimal Byzantine tolerance of less than one-fifth.
Digital money can be implemented efficiently by avoiding consensus. However, no-consensus implementations have drawbacks, as they cannot support smart contracts, and (even more fundamentally) they cannot deal with conflicting transactions. We present a novel protocol that combines the benefits of an asynchronous, broadcast-based digital currency, with the capacity to perform consensus. This is achieved by selectively performing consensus a posteriori, i.e., only when absolutely necessary. Our on-demand consensus comes at the price of restricting the Byzantine participants to be less than a one-fifth minority in the system, which is the optimal threshold. We formally prove the correctness of our system and present an open-source implementation, which inherits many features from the Ethereum ecosystem.