Proof of Authority (PoA) is a consensus method in which a small, named set of approved accounts, usually called signers or authorities, take turns producing and sealing blocks. Instead of winning the right to add a block through computing power, as in Proof of Work (PoW), or by locking up coins, as in Proof of Stake (PoS), a signer earns that right because its identity is known and its reputation is on the line. PoA is used mainly on private and consortium networks, on test networks and on some public chains that put speed ahead of openness.
The term is generally credited to Ethereum co-founder Gavin Wood; ethereum.org dates it to 2017. PoA sits at the trusted end of the spectrum that runs from fully open permissionless blockchains to closed permissioned blockchains. It is often compared with Delegated Proof of Stake (DPoS), which also relies on a short list of block producers but lets token holders vote them in, and with classic Byzantine Fault Tolerance (BFT) protocols used in enterprise ledgers.
Proof of Authority in plain terms
Picture a village notice board that only five named shopkeepers are allowed to pin notices on. Everyone in the village knows who they are, and each shopkeeper takes a turn. Nobody has to race anyone or pay a deposit for the right to post. If one shopkeeper starts pinning false notices, the others can see exactly who did it and vote to take away the key.
That is the trade PoA makes. It is fast and cheap because there are only a few trusted keepers and no contest between them. The price is that you must trust that list of keepers, and the list itself is decided by people rather than by open competition.
How Proof of Authority works
A PoA network starts with an agreed list of signer addresses written into its genesis block or configuration. Each signer runs a node and signs blocks with its private key; other nodes accept a block only if it carries a valid signature from a current authority. The best-known Ethereum design, Clique, was specified in an Ethereum Improvement Proposal (EIP) numbered EIP-225. Its main rules are:
- Round-robin turns. Signers take turns in a fixed order, and a block sealed by the signer whose turn it is carries more weight than one sealed out of turn, so honest chains win small disputes.
- Rate limits on each signer. A signer may seal only one block in any run of consecutive blocks set by the size of the signer list, which stops one key from flooding the chain.
- Voting on membership. Existing signers vote to add or remove an address, and the change takes effect once more than half of them agree.
Because there is no mining contest and very few participants, blocks can be produced on a fixed timer, and confirmation is quick and predictable. Other PoA engines include Aura, used by OpenEthereum-family clients, and IBFT 2.0, a BFT-style design used in enterprise Ethereum software such as that promoted by the Enterprise Ethereum Alliance (EEA) and Hyperledger projects.
Where Proof of Authority is used
PoA's first large-scale use was on Ethereum testnets. Kovan ran on Aura, while Rinkeby and Görli ran on Clique; they gave developers fast, free test networks that could not be spammed by anyone with cheap hardware. Those PoA testnets have since been retired in favour of proof-of-stake test networks such as Sepolia, following Ethereum's own move to proof of stake.
Several production networks use PoA or a variant:
- VeChain. VeChainThor launched with a PoA design in which a fixed set of authority masternode operators, identified to the VeChain Foundation, produce blocks.
- BNB Smart Chain. The network behind BNB (BNB) uses Proof of Staked Authority (PoSA), which combines a short validator list in the PoA style with stake-weighted election of those validators.
- Private consortium chains. Banks, supply-chain groups and other members of an industry often run PoA because every participant is already a known legal entity bound by contracts.
Strengths and weaknesses
PoA's advantages are speed, low cost and a clear line of accountability. There is no energy-hungry crypto mining, no need to lock up capital, and every block can be traced to a named operator. For a business network, that maps neatly onto existing contracts and regulation.
The weaknesses mirror those strengths. A small signer set is easier to pressure, hack or collude, so PoA networks are far more centralized than open chains. If a majority of signers agree, they can censor transactions, reorganize recent history or allow double spending, much as a miner with majority power can in a 51% attack on PoW. Critics also note that "authority" depends on identity checks done off-chain, which means users must trust whoever approved the list. For these reasons PoA is rarely chosen for networks that aim to be trustless, and it is best understood as one of several consensus families alongside Proof of Burn (PoB), Liquid Proof of Stake (LPoS) and hybrid PoW/PoS designs.