A 51% attack occurs when a single network miner or group of miners controls more than half of a blockchain network’s hash rate. Theoretically, this would enable the attacker to block transactions from taking place in the blockchain, alter the sequence of new transactions, and potentially revert past transactions (referred to as “double spending”) by tampering with blockchain data.
However, a recent study indicates that executing such attacks is financially unviable within the current security setups of Bitcoin and Ethereum.
Attacking Bitcoin and Ethereum Not Worthwhile
With reference to December 31, 2023, and considering an Ethereum price of $2,279, a total staked ETH amounting to 28.8 million ETH, and a validator count of 899,840 validators, CoinMetrics’ calculations suggest that an attacker would need around $34.39 billion to execute a 34% attack on the network.
If the assault were to commence on December 31, 2023, it would require the attacker until June 14, 2024, to breach the 33% threshold to gain control over the network.
Attacking Bitcoin would also prove to be equally far-fetched. Researchers estimate that the attacker would face production expenses of over $20 billion, as they would need to manufacture nearly 40 million units of the S9.
Using the most powerful ASIC available, like the upcoming Bitmain S21, would cost around $5.6 billion by December 2023, roughly a quarter of the expense of using the S9. This estimation is based on a unit cost of $2,240 and a production volume of 2.5 million machines.
While more cost-effective than the “naive” approach, the research asserted that manufacturing at this efficiency and scale would require cooperation with the manufacturer. However, the attacker would probably encounter supply chain issues and potential retaliation.
“Our findings suggest that the current state of security in Bitcoin and Ethereum makes attacks economically unfeasible and provides empirical evidence of Nash Equilibrium in these networks.”
The study concluded that the security measures of Bitcoin and Ethereum have reached a level where the costs and dangers linked with 51% attacks significantly outweigh the potential benefits. It indicates that hostile actions become less appealing when compared to alternative strategies like honest engagement in the network or refraining from attacking.
51% Attack Risks Extend Beyond Leading Blockchains
The assessment may be true for top blockchains like Bitcoin and Ethereum, but the same cannot be said for many other networks that have surfaced in the past decade.
Bitcoin SV, a blockchain formed as a split from Bitcoin Cash and championed primarily by entrepreneurs Calvin Ayre and Craig Wright, experienced three instances of 51% attacks in 2021. Similarly, the lesser-known privacy-focused crypto Firo, previously known as Zcoin, faced a similar ordeal. Even Ethereum Classic wasn’t spared by rogue actors.
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