Getting started with blockchain: Why do bitcoin transfers have to wait for 6 confirmations before they arrive?

Many small partners who have just been in contact with the blockchain may be surprised to see that "bitcoin transactions require six blocks to confirm." Why do you need 6 blockchain confirmations? Does it mean that 6 bitcoin miners on the Internet confirm it?

Today, Dabai will explain the principle to everyone.

In the article "What is 51% of the power attack" , Dabai introduced to you that after successfully launching a 51% power attack, you can achieve double flowers. Let's briefly review the process of double flowering:

Suppose Xiaohe sends 666BTC to Dabai and is packaged in the Nth block. Within a few minutes, Xiaohe repented. Through his own control of more than 50% of the calculation power, he launched a 51% power attack. By eliminating the 666BTC transaction sent to Dabai, the Nth block was reorganized and reorganized. The Nth block continues to extend the block, making it the longest legal chain.

This is the process of double flowers, the little black hair to the white 666BTC was invalidated.

From the above example, we can see that even if Dabai received the 666BTC from Xiaohei, the transaction was packaged and the transaction was likely to be invalidated.

In order to avoid the loss caused by double flowers, it is generally believed that the bitcoin transactions after the confirmation of the six blocks are basically not tamperable. That is to say, if the little black hair gives the big white 666BTC the transaction is packaged in the Nth block (the first block confirmation), Dabai waits until the N+5th block appears (the sixth area) Block confirmation), the transaction is basically impossible to tamper with.

Please note that the term "basically" is used here, not absolute.

Not long ago, there was a hacking and stealing incident in the currency security. A total of more than 7,000 bitcoins were stolen. The bitcoin was transferred by hackers and the transaction records were packaged at block height 575013. Shortly after the accident, some people proposed to reorganize the block . At that time, there were already many blocks confirmed.

Block reorganization means that, starting from the block where the hacker turns away from Bitcoin, the hacker's transaction record is removed, and that block and all subsequent blocks are recreated. As shown below:

It is said that after the incident of the money thief, the CZ of the currency security called Wu Jihan of Bit China, and the matter was reorganized through the bitcoin blockchain. At the time, they were able to combine the larger bitcoin computing power, from a technical point of view, the ability to reorganize and make the reorganization chain the longest legal chain of Bitcoin. How to calculate how long it takes to become the longest legal chain after reorganization, you can refer to the tweet of the vernacular blockchain school, "Kuan An 7,074 bitcoin stolen, if the block reorganization has a high probability of success, get back . "

When the reorganization news came out, the industry was in a daze, and all kinds of controversy continued. Of course, in the end, there is no reorganization, and the currency is willing to bear all the losses of hacking money.

In general, the more blocks that are confirmed, the more secure they are, the less likely they are to be tampered with and reorganized after 51% of attacks. As for the bitcoin transactions we often see, it is safe to confirm the 6 blocks. This number 6 is not mandatory. It is only said that there are 6 blocks to confirm that the possibility of being tampered is very low because of hacking or attack. It is currently difficult to master a large amount of bitcoin computing power to do evil.

Bitcoin packs an average block every 10 minutes, and 6 blocks confirm that it takes 60 minutes to average. So, do we have to wait for more than 60 minutes for every bitcoin transaction?

Actually not. For small transactions, there is no need to wait for 6 block confirmations, as the probability of a 51% power attack on Bitcoin is small. Generally speaking, bitcoin transactions of less than US$1,000 can be confirmed by 1 block; bitcoin transactions of 1000~10000 USD, general trading platform recharge and withdrawal will require at least 3 blocks to confirm; Bitcoin transactions of up to $100,000 basically require 6 block confirmations; for transactions greater than $100,000, the number of blocks identified is as high as possible.

When you make a bitcoin transfer, how many blocks are you waiting for confirmation? Welcome to leave a message in the message area.

Author | JackyLHH Produced | Vernacular Blockchain (ID: hellobtc)

『Declaration : This series of content is only for the introduction of blockchain science, and does not constitute any investment advice or advice. If there are any errors or omissions, please leave a message.