What is AuRa (Authority Round)?

AuRa (Authority Round) is a proof-of-authority consensus mechanism where a set of known, authorized validators takes turns producing blocks in a round-robin fashion. Each validator is assigned specific time slots, and when their turn arrives, they create and sign a new block. If a validator fails to produce a block during their assigned slot, the slot is skipped and the next validator in the rotation takes over. The validator set is managed through an on-chain contract that can add or remove validators based on governance decisions. AuRa is designed for networks where the validators are known entities, and trust is derived from the identity and reputation of the validators rather than from economic stake or computational work.

AuRa provides fast block times (typically 5 seconds) and deterministic finality after a sufficient number of subsequent blocks are produced. The protocol is simple and efficient, with minimal communication overhead since validators only need to produce blocks during their assigned slots rather than engaging in multi-round voting. The trade-off is centralization — the validator set must be trusted, and the network's security depends on the integrity of the authorized validators. AuRa includes mechanisms for reporting and removing misbehaving validators, such as those who produce blocks out of turn or attempt to create conflicting blocks. The protocol works well for networks with a moderate number of validators where the participants are known and accountable.

AuRa is used by the Gnosis Chain (formerly xDai Chain), which merged with the Gnosis ecosystem and transitioned to a broader validator set. It is also used by the Fuse Network and has been implemented in the OpenEthereum (formerly Parity Ethereum) client. Gnosis Chain originally used AuRa with a small set of trusted validators before expanding to a larger proof-of-stake validator set. The Fuse Network uses AuRa for its payment-focused blockchain. AuRa was developed by Parity Technologies and is available as a consensus option in the OpenEthereum and Nethermind clients, making it a practical choice for permissioned or semi-permissioned EVM-compatible networks that prioritize simplicity and performance over maximum decentralization.