Definition
Proof of Authority (PoA) is a consensus mechanism used mainly in permissioned blockchains, where a small set of pre-approved, publicly identified validators take turns producing blocks. Rather than staking energy or capital, these authorities stake their real-world identity and reputation, which is forfeited if they misbehave. It is included here for completeness; it is a centralized design unsuited to Bitcoin's permissionless goals.
How validators are chosen
Validator status is granted through vetting: candidates typically must disclose a verifiable identity, demonstrate good standing, and be admitted by governance. Because the validator set is small and known, blocks are produced quickly and cheaply, often in a round-robin order, with consensus reached without resource-intensive competition. This makes PoA attractive for consortium networks, supply-chain ledgers, and Ethereum test networks where throughput and low cost matter more than openness.
The decentralization trade-off
PoA's efficiency comes from concentrating trust in a handful of named parties. That same concentration is its core weakness for public use: a few validators can in principle censor transactions or collude, and the network's integrity depends on the honesty and continued availability of those specific operators. PoA is therefore best understood as a deliberate trade of decentralization for performance, appropriate only where participants already trust the authorities.
For permissionless alternatives that avoid this trust concentration, see Proof of Stake and the energy-anchored model in Nakamoto Consensus.
In Simple Terms
Proof of Authority (PoA) is a consensus mechanism used mainly in permissioned blockchains, where a small set of pre-approved, publicly identified validators take turns producing…