How Blockchain Works: Majority Rules
When a new transaction occurs, it is packaged into a 'block' and then added to the end of the ledger. To ensure that no one can secretly modify the transaction, this system has a core principle: majority rules. That is to say, if the vast majority of computers agree that the transaction is real and valid, it will be recorded, and once recorded, it is difficult to tamper with.
What is a 51% Attack?
Now, imagine if there is a person or organization that controls more than half (that is, 51% or more) of these computers that maintain the ledger. If they really achieved this, they would have enormous power and could do some bad things. The attack that occurs in this situation is called a 51% attack.
What Can a 51% Attack Do?
If the attacker controls more than half of the computing power (that is, the ability to process transactions), they can:
Preventing New Transactions from Being Confirmed:
They can prevent others' transactions from being recorded in the ledger, thus disrupting the normal operation of the entire network.
Double Spending:
This is the most dangerous situation. Imagine the attacker uses 100 bitcoins to buy something, and then they utilize the controlled computing power to erase this transaction from their own ledger and spend those 100 bitcoins on another person. In this way, they effectively spend the same money twice.
Why is it Difficult for a 51% Attack to Occur?
It sounds scary, but for large cryptocurrencies like Bitcoin and Ethereum, launching a 51% attack is extremely difficult for several reasons:
Extremely High Cost:
Controlling 51% of the computing power requires astronomical amounts of money to purchase and operate a large number of specialized mining machines (computers that maintain the ledger). This investment is difficult for any individual or organization to bear.
Low Returns:
Even if the attack is successfully launched, the attacker will find that the returns are not high. Once the attack is discovered, the value of the cryptocurrency will plummet, and the coins held by the attacker will become worthless, making it a loss.
The Community Will Fight Back:
The blockchain community is decentralized. If signs of a 51% attack appear, community members will quickly take action, such as adjusting the consensus mechanism or simply creating a new blockchain, rendering the attacker's efforts futile.
Summary
Therefore, a 51% attack refers to an attacker controlling more than half of the computing power in the blockchain network, allowing them to manipulate transactions. Although this possibility exists theoretically, it is very difficult for mainstream cryptocurrencies due to the enormous costs and risks, as well as the strong community power. The decentralized nature of blockchain and the robust consensus mechanism make it very secure in the vast majority of cases.
