Many small partners who have just been in contact with the blockchain may be puzzled when they see that “Bitcoin transactions require 6 block confirmations”. Why do we need 6 blockchain confirmations? Is it confirmed by the 6 Bitcoin miners on the entire network?
Today, Da Bai will explain to you the principles.
In the article “What is a 51% hashrate attack” , Dabai introduced to everyone that after successfully launching a 51% hashrate attack, double spending can be achieved. Let’s briefly review the process of double spending:
Suppose that Xiao Hei sends 666 BTC to Da Bai and is packed into the Nth block. Within a few minutes, Xiao Hei repented and launched a 51% attack with more than 50% of the computing power under his control. By removing the 666 BTC transaction sent to Da Bai, he reorganized the Nth block and was reorganizing it. Continue to extend the block after the Nth block to make it the longest legal chain.
This is the process of double spending. The 666 BTC given to Dabai by the little black hair is invalidated.
From the above example, we can see that even if Dabai received the 666 BTC transferred from Xiaohei at the time, and the transaction was packaged on the chain, the transaction might be invalidated.
In order to avoid losses caused by double spending, it is generally believed that Bitcoin transactions after 6 blocks are confirmed cannot be tampered with. In other words, if the transaction of 666 BTC given to Dabai by the little black hair is packaged in the Nth block (the first block is confirmed), Dabai waits until the N+5th block appears (the sixth block). Block confirmation), this transaction basically cannot be tampered with.
Please note that “basically” is used here, not absolute.
Not long ago, there was a hacking incident in Binance. A total of more than 7,000 bitcoins were stolen. The bitcoins were transferred by the hackers. The transaction records were packaged at block height 575013. Soon after the accident, someone proposed a block reorganization. At that time, many blocks had been confirmed.
Block reorganization means that starting from the block where the hacker transferred Bitcoin, the hacker’s transaction records are removed, and that block and all subsequent blocks are recreated. As shown below:
It is said that after the stolen currency incident, Binance’s CZ called Wu Jihan of Bitmain and talked about the reorganization of the Bitcoin blockchain. At that time, they were able to combine relatively large Bitcoin computing power, and from a technical point of view, they were able to reorganize and make the reorganization chain the longest legal chain of Bitcoin. How to calculate how long it will take to become the longest legal chain after the reorganization can refer to the tweet of the vernacular blockchain school “Binance 7074 Bitcoins were stolen, if the block reorganization is successful, how likely is it to get it back”.
As soon as the news of the reorganization came out, the industry was in an uproar, and various controversies continued. Of course, there is no reorganization in the end, and Binance is willing to bear all the losses of hackers stealing coins.
Generally speaking, the more blocks that are confirmed, the more secure, and the lower the possibility of tampering and reorganization after a 51% attack. As for the Bitcoin transaction that we often see that it is safe after 6 blocks are confirmed, the number 6 is not a hard and fast rule. It just means that with 6 block confirmations, the possibility of tampering is very low due to hackers or attacks. It is currently difficult to master a large amount of Bitcoin computing power to do evil.
Bitcoin packs a block every 10 minutes on average, and it takes an average of 60 minutes to confirm 6 blocks. So do we have to wait more than 60 minutes for every bitcoin transaction?
Actually not. For small transactions, there is no need to wait for 6 block confirmations, because the probability of 51% attack on Bitcoin is very small. Generally speaking, for Bitcoin transactions less than USD 1,000, one block confirmation is sufficient; for Bitcoin transactions between USD 1,000 and 10,000, general trading platform deposits and withdrawals require at least 3 block confirmations; between 10,000 Bitcoin transactions of ~100,000 USD basically require 6 block confirmations; for transactions greater than 100,000 USD, the more blocks confirmed, the better.
Posted by:CoinYuppie，Reprinted with attribution to:https://coinyuppie.com/why-does-bitcoin-transfer-have-to-wait-for-6-confirmations-to-arrive/
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