Chances of 51% Attack

What is a 51% attack?

51% attack is also known as a majority attack, which occurs when a single person or group of people gains control of more than 50% of the hash power of a blockchain, which is usually done by leasing the mining Hash power to a third party.

Successful attackers are allowed to block confirmation of new transactions and rearrange the order of new transactions. It also allows malicious brokers to essentially rewrite parts of the blockchain and reverse their transactions, creating a problem known as double-spending. Traditionally, this problem has mainly occurred with electronic payments, where a network has not been able to show that two or more people are not spending the same digital asset. 

However, a 51% attack is theoretically limited in the amount of interference it can cause. While the attacker could trigger the double-spending problem, they cannot reverse the transactions of others on the network or prevent users from transmitting their transactions over to the network. In addition, a 51% attack cannot create new assets, steal assets from independent parties, or change the functionality of block rewards. 

Chances of 51% Attack

As a blockchain network grows and acquires news mining nodes, the chance of a 51% attack is lower. Basically, the larger the network and when more nodes participate, the more hash power is required to control more than 50% of it. But even if an attacker exceeded 50% of the hash rate, the size of a blockchain could still provide security. Since blocks in the chain are linked, a block can only be changed if all subsequently confirmed blocks are removed. 

While this would be possible, it would be incredibly costly for the attacker for two reasons: The attacker would have to use a lot of computing power (electricity costs) to achieve a hash rate of 51%, especially in larger, more established networks. If the miner does not behave appropriately, he would no longer receive the blockchain rewards that come with mining. So the more transactions there are, the more blocks there are in the chain and the more difficult it is to change a block.

While large blockchains like Bitcoin are still at risk of a 51% attack, the financial costs would far outweigh the benefits. Even if an attacker were to devote all of their resources to attacking a blockchain, the constant addition of the blocks to the chain would only give a relatively small window for several transactions that the attacker can change.

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