Solana is the Ethereum killer?
Solana is a high-performance blockchain taunted to solve the blockchain scalability problem
A 51% attack also known as the majority attack refers to a malicious actor or a group acting in concert, controlling the majority of the total mining power of the blockchain network and disrupting the integrity of the blockchain. This attack is one of the most serious attacks on a blockchain impacting its security and decentralization.
Public blockchain requires consensus to function - to accept new blocks, transactions. A threat actor controlling the majority of the hashing power in a proof of work blockchain can disrupt the integrity of the blockchain by modifying the order of transactions, preventing legitimate transactions from being confirmed, or double-spending the coins. In a proof of stake blockchain, the attacker would require 51% of total coins.
The risk of a 51% attack is higher for blockchains with less hashing power or where the number of miners are less making it is easier for a malicious actor to achieve the majority. However, this attack is very unlikely on the Bitcoin blockchain because of a large number of independent miners and high hashing power making it impossible for a single person or entity to achieve the computing power required to obtain the majority.
The more miners in a network and the higher the amount of hashing power required makes it difficult to perform 51% attacks. Smaller blockchain networks like Bitcoin Gold (BTG) suffered 51% attacks multiple times. In 2018, malicious actors could double-spend BTG for several days ending up stealing more than $18 million worth of BTG. This coin was hit again in 2020.
Recently, the Bitcoin SV, a hard fork of the Bitcoin Cash network suffered a 51% attack in August 2021. Ethereum Classic (ETC), which forked from the original Ethereum blockchain has seen 51% attacks several times.
In June 2018, the developer team behind BTG upgraded the algorithm from Equihash based on the parameter set <200,9> to <144,5>, with some customization to improve security and prevent 51% attacks.
It is for this reason, most crypto exchanges require multiple block confirmations before letting users withdraw funds or trade. When a transaction has been included in a block by a miner, the block needs to be validated by the other nodes on the network. Once confirmed by other miners, the transaction is considered to have a single confirmation, and all new blocks that follow will represent another confirmation. This allows exchanges to hold on to the funds in case of a 51% attack creating double-spending.
The actual number of confirmations before a transaction is considered final varies and is directly dependent on the computational power (hash rate) devoted to securing each blockchain network. For instance, WazirX requires only 4 confirmations for Bitcoin while 100 confirmations are required for Bitcoin SV.