Editor's note: This article is from Hashpai (ID: hashpai), author: not broken, published with authorization.

The so-called 51% computing power attack refers to using one's own computing power advantage to tamper with the records on the blockchain, so as to achieve the purpose of canceling the paid transaction.

Bitcoin transaction data is actually packaged and recorded by miners through computing power competition. "Computing power" refers to the number of times the hash value can be calculated per second. The greater the computing power, the faster the calculation speed of the miner. In theory, when a person has more than 51% of the computing power, he can calculate the correct hash value faster than other miners in the whole network, so as long as he starts from the transaction data that he wants to tamper with If a block starts to mine down, it is possible for him to create a longer blockchain than the current main chain.

In the POW mechanism, when a node receives a longer block chain from other nodes, it will automatically abandon the current chain and continue mining on the new main chain, so that it has 51% computing power. Strong miners can undo previous transaction records. So under normal circumstances, after we initiate a transfer, we have to wait at least six blocks for confirmation before it can be regarded as an immutable transaction. Because the more blocks that need to be tampered with, the more difficult it is to achieve.

Although it is possible to launch a 51% computing power attack from the current situation where Bitcoin mining computing power is becoming more and more concentrated, from the perspective of economic benefits, launching an attack is not beneficial to miners. First, once a computing power attack occurs, the security of Bitcoin will be questioned, which will lead to a sharp drop in price; No bitcoin rewards can be obtained on the website.