What is a 51% Attack?

Note: Sorry, I have missed the last couple days of posts! Got a good one today! Enjoy - Ben

51% Attacks

Because blockchains are decentralised and not controlled by a central authority, it makes them vulnerable to 51% attacks.

A 51% attack is an attack on a cryptocurrency blockchain., when a group of miners own more than 50% of the mining hash rate.

This would give them controlling power to alter the blockchain:

A majority controlling group could prevent new transactions, and reverse transactions, which could allow them to double spend tokens.

Consensus mechanisms are put in place to prevent attacks:

Attacks are costly!

For example the most advanced ASIC miner, Bitmain S19 XP Hydro, costs 88,400 new and has a rate of 256 terahashes per second (TH/s).

To control 66.87% of the hash rate, which is the combined total of the top three mining pools (242 million TH/s).

Let's do the math

The CPU in your computer could maybe hash 15 kilo hashes per second.

To equal the hash rate would require 941,64 S19 XP Hydros, for a fixed cost of $7.9 billion. Before adding the cost of housing equipment, maintenance, electricity and cooling.

Acquiring this amount of power is obviously costly.

But what if we looked at a different blockchain.

For example, Ethereum:

Ethereum is a Proof-of-Stake blockchain. To start a 51% attack a group would have to stake more than half of all staked ETH.

In 2023 19.3 million ETH were staked. An attack would have to stake 9.8 million ETH valued at $18 billion.

Once an attack is started, the network would likely recognise the attack and slash the Staked ETH, destroying the attackers measly $18 billion.

Average CPU could hash 15 kilo hashes per second

51% attacks are a definite risk to decentralised blockchains.

This is why consensus mechanisms are put in place, to make it extremely costly.

Thus, extremely unlikely.

Thanks

Ben