Understanding 51% Attacks on Bitcoin and Blockchain

What Is a 51% Attack?

A 51% attack occurs when a malevolent miner in a blockchain network gains control of the blockchain mining power. This means that the miner—in this case, an attacker— will be able to mine faster than other miners because the attacker now controls more than 50% of mining power.

Having 51% control—which is the least percentage required to take over a blockchain network—is ominous.

Difference Between a 51% Attack and a 34% Attack

A 34% attack is known with the Tangle consensus algorithm. The attacker only falsifies the blockchain’s ledger by approving or disapproving transactions. In contrast, the 51% attack gives attackers control of a blockchain such that they can disrupt mining and the entire blockchain.

Implications of a 51% Attack on Blockchain and Bitcoin

When an attacker controls 51% mining power in a blockchain, then the security of such a blockchain has been compromised, leaving the attacker in control of transactions. Below are the implications of what’s bound to happen due to a 51% attack:

1. Network Disruption by Delaying Validation of Transactions: The attacker disrupts the blockchain network by attacking the miner’s computing resources. In such a scenario, there’ll be a delay in the validation and storage of transactions in a block. As a result, the blockchain is hampered, causing the attacker to process transactions faster than the miners or even prevent another miner from adding blocks.
2. Double Spending: Double spending occurs when miners spend their crypto twice on a particular blockchain network.How?
   Imagine if the attacker had previously purchased a Ferrari 250 GTO with 1,600 BTC; he paid for the car and got the delivery of the vehicle. During a 51% attack on the BTC blockchain, the attacker can reverse the 1,600 BTC transferred to the seller’s wallet such that he keeps the car and the BTC. The BTC can then be spent for another purpose. This is known as double-spending.
3. Reduction in Miner’s Reward: Since miners are usually rewarded for validating transactions on a blockchain, in the wake of a 51% attack, the attacker steals the shares of other miners, making them earn less than what they’re supposed to earn.

Diminishes Blockchain’s Credibility

A 51% attack on a blockchain network will diminish the credibility of such a blockchain. Both miners and investors will not trust the security framework anymore. This might lead to abandoning the project or some exchanges delisting the crypto from their market.

Below are the examples of blockchains that have suffered a 51% attack:• BSV—Bitcoin Satoshi Vision—was attacked in August 2021• ETC—Ethereum Classic—was attacked thrice in August 2020

• BTG—Bitcoin Gold— was attacked twice; once in 2018 and then in 2020

• GRIN was attacked in 2020, the attacker controlled about 58% of GRIN’s hash rate

• VTC—Vertcoin—was also attacked twice in 2019

How to Prevent 51% Attack

i. Limited Hash Power – Blockchains running on the PoW mechanism should limit the hash power of each miner to 50% or lesser. This will pre-empt such an attack

ii. Using PoS or DPoS A PoS- Proof-of-Stake- the mechanism is another consensus mechanism for validating blockchain transactions. It is eco-friendly because no power is needed, and it doesn’t require a sophisticated machine. PoS uses coin owners’ machines to mine crypto. Investors stake their coins in return for an opportunity to validate blocks.DPoS, on the other hand, means Delegated Proof-of-stake. It is a decentralized PoS where the crypto community appoints validators by voting. If a validator is perceived to be compromising the network, they are also voted out by the community.

Conclusion

A 51% attack doesn’t mean the attacker can send BTC from your wallet or account; it only means the blockchain has been compromised, and double-spending of crypto is imminent. Blockchains like Bitcoin and its contemporaries, with larger mining nodes and hash power, are less likely to be attacked due to the financial cost involved.

By Abubakar Maruf