A consensus algorithm in blockchain technology can be either permissionless or permissioned. The blockchains of Bitcoin (BTC) and Ethereum (ETH) are permissionless. While the blockchain of a tech company called Apla is permissioned. 

About Permissioned Blockchain

  1. Pre-authenticated nodes are present in a permissioned blockchain
  2. Therefore, PoA can be used in the permissioned blockchain to provide a high transaction rate and other benefits. 

In PoA, if a node passes a preliminary authentication, then the node will gain authority for the creation of a new block. 

Advantages of PoA

  1. Nodes don’t require high-performance hardware. The spending of computational resources is not required to solve mathematical equations
  2. The prediction of the interval of time at which a node creates a new block is possible. The interval of time varies for consensus protocols like Proof-of-Work (PoW) and Proof-of-Stake (PoS)
  3. A high transaction rate is provided by PoA. Authorized network nodes create blocks in a sequence. The creation of a block requires a fixed time interval. The speed of the validation of transactions is increased
  4. The authority for the creation of blocks can be taken back. PoA will remove a node from a group of validating nodes due to the unavailability of the node for a new block to completion. 

An Example Of Denial-of-Service (DoS) Attack

A Denial-of-Service (DoS) attack is recognized as a cyber attack. In the DoS, an attacker targets users and makes machine or network resources unavailable for them. The services of a host are disrupted for a short period of time. They are also disrupted for an unlimited or unspecified period of time. 

Pre-authenticated nodes are present in a network. Therefore, nodes who can resist DoS will be provided with authorities for the creation of new blocks.

51% Attack

  1. If an attacker has control over 51% of the computational power of a network, then a 51% attack will be possible
  2. The 51% attack of PoA is not like a 51% attack of PoW
  3. If an attacker has control over 51% of the nodes of a network, then a 51% attack will be possible.
  4. It is difficult to gain control over nodes in a permissioned blockchain network.

* In PoW, if an attacker increases the computation power of the controlled network segment, then the controlled percentage will be increased. In PoA, the decision in a network will not be affected by the computational power of a node. 

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