A 51% attack refers to the act of using this computing power to recalculate confirmed blocks after mastering 51% of the Bitcoin network's computing power, so that the blockchain can fork and gain benefits.
Assuming that the person who launched the 51% attack is a rational person, the purpose of the attack is for benefit, not for others. Therefore, the attacker has two conditions before launching the attack:
- Mastered 51% of the computing power of Bitcoin's entire network
- Hold a lot of Bitcoin in your hand
Attacker launches an attack
Transfer bitcoins to an exchange or an institution or individual, sell all bitcoins, receive the money, and withdraw the money to the bank account (the purpose of the withdrawal is to ensure profit, and it is not necessary to withdraw it). The shorter this time, the better, which can greatly save attack time.
Use 51% of the computing power to regenerate the block from the block that has not yet been transferred to the exchange
For example, if the block to transfer coins to the exchange is the 300,000th block, the attacker will start to regenerate the block at the 299999th block.
Because the attacker has 51% computing power, and assuming that he can guarantee 51% computing power during the attack process, his attack must be successful, which means that the attacking block chain he generated must be able to catch up with the original block chain.
When the length of the attacking block chain exceeds 2 blocks of the original block chain, all clients will discard the original block chain and accept the attacking block chain. So far, 51% of the attacks were successful.