Proof-of-Activity (PoA) is a blockchain consensus algorithm that facilitates genuine transactions and consensus amongst miners. That is a consensus algorithm combining proof-of-work and proof-of-stake. This consensus algorithm is designed to prevent attacks on the underlying Blockchain.
Proof-of-Activity is a combination of Proof-of-Work (PoW) and Proof-of-Stake (PoS).
Proof-of-Work is the most common consensus algorithm and is utilized by Bitcoin among other cryptocurrencies. While PoW maintains blockchain integrity and security, it does consume vast amounts of computing power and electricity. There are also issues with scalability and centralization, with most of the hashing power held by a select few individuals or groups.
Proof-of-Stake remedies the resource intensiveness of PoW but also suffers from a form of centralization. In this case, centralization is caused by early adopters who earn a larger share of block creation fees and discourage late adopters from participating.
Proof-of-Activity was first proposed in a research paper in 2014. In the abstract of the paper, the authors “propose a new protocol for a cryptocurrency, that builds upon the Bitcoin protocol by combining its Proof-of-Work component with a Proof-of-Stake type of system. Our Proof-of-Activity (PoA) protocol offers good security against possibly practical attacks on Bitcoin, and has a relatively low penalty in terms of network communication and storage space.“
How blocks are generated in a PoA network
The following steps dictate the block creation process in a PoA network:
- To start, each miner uses hash power to try and generate an empty block header. This is header data consisting of the hash of the previous block, the miner’s address, the height relative to the genesis block, and a nonce. It’s important to note that the header does not include past transactions.
- A miner succeeds in generating a block header when the hash of their block header data is less than the current difficulty target. Once successful, the block header is broadcasted to the network.
- The hash of the block header is linked with the hash of the previous block. Each combination is then hashed and follow-the-satoshi is invoked with each hash acting as input. Follow-the-satoshi is a PoA subroutine, which transforms a pseudorandom value into a small unit of cryptocurrency called a satoshi. Each satoshi is picked randomly from the satoshis that have been already mined.
- Active miners then check whether the block header from step two is valid. Does it contain the hash of the previous block and does it meet the current difficulty? After validation, each miner determines whether they are one of the stakeholders of the block. Successful miners sign the hash block header with a private key that determines their satoshi and broadcasts their signature to the network. This process is repeated until every chosen validator signs the block.
- The last miner to sign the block then broadcasts the wrapped block to the network. The block is considered a legitimate extension of the blockchain once other nodes see validity in the above four steps. Similar to the Bitcoin blockchain, the nodes try to extend the longest branch they are aware of by assessing PoW difficulty. The fees collected by the last miner are shared between themselves and the remainder of the “winners”.
Protection against malicious attacks
Both PoS and PoW were designed to prevent 51% attacks, where one individual or party attempts to gain majority control over mining power.
However, PoA adds another layer of protection against such attacks. In theory, a malicious actor would need to have 51% or more of the total mining power in addition to 51% or more of the coins staked in the network.
- Proof-of-Activity (PoA) is a hybrid of the PoS and PoW consensus mechanisms. It facilitates genuine transactions and consensus among miners.
- PoA attempts to address centralization issues in both PoS and PoW. It also seeks to do so in a manner that is not resource-intensive.
- The probability of a 51% attack on a PoA system is reduced significantly. This is because a malicious actor would need majority control of both the mining hash rate and the number of coins in a system.
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