What Is a 51% attack?

What Is a 51% attack?

A 51% attack, also known as a majority attack, occurs when one or more persons gain control of over 50% of a blockchain’s hashing power.

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04 Aug, 2022
3 mins

A 51% attack, also known as a majority attack, occurs when one or more persons gain control of over 50% of a blockchain’s hashing power. This enables the attacker to have control over the network and potentially disrupt the network process.

How does it work?

Although 51% of attacks are hard to complete, they are not as hard to comprehend.

1.   Accumulating mining or validation power: Cryptocurrencies operate through a distributed network and use mainly a PoW or PoS consensus mechanism for the nodes to communicate and operate the network. A miner would require a massive amount of computing power to attack a PoW chain or more than 50% of the stake in a PoS blockchain network. This process is costly and logistically prohibitive. It is less likely to succeed with a more decentralized network such as Bitcoin.

2.   In the off chance that an attacker gains control: If successful, the attacker can prevent the recording and validation of transactions, prevent mining by anyone other than themselves, change transaction order, reverse transactions, and double-spend coins. There have been notable successes of a 51% attack, such as the Bitcoin Gold attack in 2018 that led to the theft of $18 million and Ethereum classic in 2019 that led to the theft of $1.1 million. On the other hand, the attacker is not able to change block rewards, create new coins, or steal coins that never belonged to them. Moreover, an attacker will only be able to modify a few of the recent blocks for a short period of time.

Logistically, miners that manage to accumulate 51% of the mining power would probably make more money mining legitimately than trying to control the network. Additionally, the growth of a centralized hashing power will be noticed, and the community will be able to adapt accordingly. Furthermore, the more decentralized a network is or the higher its hash rate, the more expensive it becomes to perform a majority attack, thus making it almost impossible to happen.


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