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Proof of Authority consensus

In blockchain platforms, consensus mechanisms can be divided into permissionless (eg., Ethereum, Bitcoin) and permissioned (eg Hyperledger, Ethereum Private). Unlike permissionless blockchain where anyone can become node, in permissioned blockchain all nodes are pre-selected. This allows to use consensus types with high scalability and bandwidth. One of these consensus types is Proof-of-Authority (PoA) consensus which provides high performance and fault tolerance. Term was proposed in 2017 by co-founder of Ethereum and Parity Technologies Gavin Wood.

Working of PoA :

PoA consensus and common attacks :

  1. Distributed Denial-of-service attacks(DDos) :
    A Distributed Denial of Service (DDoS) attack is an attempt to make an online service unavailable by overwhelming it with traffic from multiple sources. An attacker sends large number of transactions and blocks to targeted network node in an attempt to disrupt its operation and make it unavailable.

    PoA mechanism makes it possible to defend against this attack because network nodes are pre-authenticated, block generation rights can be granted only to nodes that can withstand DoS attacks.

  2. 51% attack :
    In PoA consensus, 51% attack requires an attacker to obtain control over 51% of network nodes. This is different from 51% attack for the Proof-of-Work consensus types where an attacker needs to obtain 51% of network computational power. Obtaining control of the nodes in permissioned blockchain network is much harder than obtaining computational power.

    With PoA, individuals earn right to become validators, so there is an incentive to retain position that they have gained. Validators are incentivized with reputation which lets them retain their authority as a node. PoA only allows non-consecutive block approval from any one validator, meaning that the risk of serious damage is centralized to the authority node.

Conditions for PoA consensus :

Advantages of PoA consensus :

Limitations :

Application of PoA consensus :

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