Basic meaning of blockchain

Blockchain （blockchain） It's a big hit right now , The news media reported a lot , Claim that it will create the future .

But , There are few easy to understand introductory articles . What is blockchain , What's special , There is little explanation .

below , I'll try , Write a best understanding of the blockchain tutorial . After all, it's not very difficult , The core concept is very simple , You can make it clear in a few words . I hope to finish reading this article , You can not only understand blockchain , And understand what mining is 、 Why is mining more and more difficult .

It should be noted that , I'm not an expert on this . Although I have been concerned about , But take a closer look at the blockchain , Or from the beginning of this year . Mistakes and inaccuracies in the text , Welcome to correct .

One 、 The essence of blockchain

What is blockchain ？ In a word , It's a special kind of distributed database .

First , The main function of blockchain is to store information . Any information that needs to be saved , Can be written to the blockchain , You can also read from it , So it's a database .

secondly , Anyone can set up a server , Join the blockchain network , Become a node . In the world of blockchain , There is no central node , Every node is equal , They hold the entire database . You can go to any node , write in / Reading data , Because all nodes will eventually synchronize , Ensure that the blockchain is consistent .

Two 、 The biggest characteristics of blockchain

Distributed database is not a new invention , There have been such products in the market . however , Blockchain has a revolutionary feature .

Blockchain has no administrator , It's completely centerless . Other databases have Administrators , But blockchain doesn't have . If someone wants to add audit to blockchain , It doesn't work , Because it's designed to prevent the emergence of central management .

It's because of the inability to manage , Blockchain can not be controlled . Otherwise, once large companies and groups control the management power , They will control the whole platform , Other users have to obey them .

however , Without the Administrator , Everyone can write data into it , How can we ensure that the data is credible ？ What to do if you are changed by a bad person ？ Please read on , That's the magic of blockchain .

3、 ... and 、 block

A blockchain consists of blocks （block） form . Blocks are like records in a database , Every time you write data , It's creating a block .

Each block contains two parts .

• Block head （Head）： Record the eigenvalues of the current block
• Block body （Body）： Actual data

The block head contains multiple eigenvalues of the current block .

• Generation time
• Actual data （ That is block body ） Hash
• Hash of the previous block
• ...

here , You need to understand what Hash （hash）, This is necessary to understand the blockchain .

So-called " Hash " That is, the computer can handle any content , Calculate an eigenvalue of the same length . Block chaining The hash length is 256 position , That is to say , No matter what the original content is , At the end of the day, we'll figure out a 256 Binary number of bits . And it can guarantee , As long as the original content is different , The corresponding hashes must be different .

for instance , character string 123 The hash of is a8fdc205a9f19cc1c7507a60c4f01b13d11d7fd0（ Hexadecimal ）, To binary is to 256 position , And only 123 You can get this hash .（ Theoretically , Other strings can also get this hash , But the probability is very low , It can be approximated that it can't happen .）

therefore , There are two important corollaries .

• inference 1： The hash of each block is different , Blocks can be identified by hashing .
• inference 2： If the content of the block changes , Its hash is bound to change .

Four 、 Hash The immutability of

Blocks and hashes are one-to-one correspondence , The hash of each block is for " Block head "（Head） Calculated . in other words , Put the eigenvalues of the block into the matrix , Connect in order , Make up a very long string , Then hash the string .

Hash = SHA256( Block head )

The above is the calculation formula of block hash ,SHA256 It's the hash algorithm of blockchain . Be careful , This formula only contains block heads , Does not contain block bodies , in other words , The hash is uniquely determined by the block header ,

As I said before , The block header contains a lot of content , There is the hash of the current block body , And the hash of the last block . It means , If the content of the current block body changes , Or the hash of the previous block has changed , It will definitely cause the hash of the current block to change .

This is of great significance to the blockchain . If someone modifies a block , The hash of the block changes . So that the blocks behind can still connect to it （ Because the next block contains the hash of the previous block ）, The person has to modify all the following blocks in turn , Otherwise, the changed block will be separated from the blockchain . For the reasons to be mentioned later , Hashing is time consuming , It is almost impossible to modify multiple blocks in a short time , Unless someone's got the whole network 51% The above computing power .

It is through this linkage mechanism that , Blockchain ensures its own reliability , Once the data is written , It can't be tampered with . It's like history , What happened is what happened , From then on, there is no way to change .

Every block is connected , This is also " Blockchain " The origin of the name .

5、 ... and 、 mining

Because the synchronization between nodes must be guaranteed , So the speed of adding new blocks should not be too fast . Just imagine , You just synced a block , Ready to generate the next block based on it , But at this time, other nodes have new block generation , You have to give up half the calculation , To synchronize again . Because behind each block , You can only follow one block , You can always be behind the latest block , Generate the next block . therefore , You have no choice , On hearing the signal , You have to synchronize immediately .

therefore , Nakamoto, the inventor of blockchain （ It's a pseudonym , The real identity is still unknown ） Intentionally let new blocks be added , It becomes very difficult . His design is , The average 10 minute , Only the whole network can generate a new block , Six in an hour .

This output speed is not achieved by command , It's deliberately setting up massive computing . in other words , Only through an extremely large amount of calculation , To get a valid hash of the current block , So as to add new blocks to the blockchain . Because of the amount of calculation , So I can't get up soon .

This process is called mining （mining）, Because of the difficulty of calculating a valid hash , It's like in the sand all over the world , Find a grain of sand that meets the criteria . The machine that calculates the hash is called a miner , The man who operates the mining machine is called a miner .

6、 ... and 、 The difficulty coefficient

Read here , You may have a question , People say it's hard to mine , But mining is to calculate a hash by computer , That's what computers are good at , How can it be difficult , It's too late to come out ？

It turns out that not any hash can , Only those hashes that meet the criteria will be blocked . This condition is particularly harsh , Most hashes do not meet the requirements , Must recalculate .

original , The block head contains a The difficulty coefficient （difficulty）, This value determines the difficulty of hash calculation . for instance , The first 100000 Block The coefficient of difficulty is 14484.16236122.

Block chain protocol , Use a constant divided by the difficulty coefficient , You can get the target value （target）. obviously , The greater the difficulty coefficient , The smaller the target value .

The validity of hash is closely related to the target value , Only hashes smaller than the target value are valid , Otherwise the hash is invalid , Must recalculate . Because the target value is very small , The chance of a hash less than that value is extremely slim , It's possible to calculate 10 100 million times , Only once . That's why mining is so slow .

As I said before , The hash of the current block is uniquely determined by the block header . If you want to hash the same block over and over again , Means , The area has to change all the time , Otherwise, it's impossible to work out a different hash . All the eigenvalues in the block are fixed , To make the block head change , Nakamoto deliberately added a random term , be called Nonce.

Nonce It's a random value , The role of miners is to guess Nonce Value , So that the hash of the block header can be smaller than the target value , So that you can write to the blockchain .Nonce It's very hard to guess , At present, we can only try and make mistakes one by one through the exhaustive method . According to the agreement ,Nonce It's a 32 Binary value of bit , That is, it can reach the maximum 21.47 Billion . The first 100000 Block Nonce The value is 274148111, Can be interpreted as , Miners from 0 Start , I've been calculating 2.74 100 million times , To get an effective Nonce value , So that the hash can satisfy the condition .

With luck , Maybe we'll find it soon Nonce. Bad luck , Maybe it's over 21.47 100 million times , Nothing Nonce, That is, it is impossible for the current block body to calculate the hash that meets the conditions . At this time , The agreement allows miners to change the block body , Start a new calculation .

7、 ... and 、 Dynamic adjustment of difficulty coefficient

As we said in the previous section , Mining is random , There is no guarantee that a block will be produced in exactly ten minutes , Sometimes it comes out in a minute , Sometimes it doesn't work out for hours . overall , With the improvement of hardware equipment , And the increase in the number of mining machines , It's going to be faster and faster .

To keep the output rate constant for ten minutes , Nakamoto also designed the dynamic adjustment mechanism of difficulty coefficient . He stipulated that , The difficulty factor is every two weeks （2016 Block ） Adjust once . If in two weeks , The average block generation speed is 9 minute , It means faster than the legal speed 10%, So the next difficulty factor is going to be raised 10%; If the average generation rate is 11 minute , It means it's slower than the legal speed 10%, So the next difficulty factor will be lowered 10%.

The higher the difficulty coefficient is （ The target value is getting smaller and smaller ）, It makes mining more and more difficult .

8、 ... and 、 The fork of the blockchain

Even if the blockchain is reliable , Now there's another problem that hasn't been solved ： If two people write data to the blockchain at the same time , in other words , At the same time, two blocks are added , Because they're all connected to the previous block , It's a bifurcation . Which block should be adopted at this time ？

Now the rule is , New nodes always use the longest blockchain . If the blockchain has forks , We'll see which branch is behind the bifurcation point , Arrive first 6 A new block （ be called " Six confirmations "）. according to 10 One block per minute , It'll be confirmed in an hour .

Because the generation speed of new blocks is determined by the computing power , So the rule is that , The branch that has most of the computing power , It's an authentic blockchain .

Nine 、 summary

Blockchain as an unmanaged distributed database , from 2009 It's been running for years 8 year , No big problems . This proves that it works .

however , In order to ensure the reliability of data , Blockchains also have their own costs . One is efficiency , Data is written to the blockchain , Wait at least ten minutes , All nodes synchronize data , It takes more time ; The second is energy consumption , The formation of blocks requires countless meaningless calculations by miners , It's very energy intensive .

therefore , Applicable scenarios of blockchain , In fact, it's very limited .

1. There is no authority that all members trust
2. The data written is not required to be used in real time
3. The benefits of mining can make up for its own costs

If the above conditions cannot be met , So the traditional database is a better solution .

at present , The biggest application scenario of blockchain （ Maybe the only application scenario ）, It is the cryptocurrency represented by bitcoin . Next article , I will introduce Introduction to bitcoin .

Ten 、 Reference link

• How does blockchain really work?, by Sean Han
• Bitcoin mining the hard way: the algorithms, protocols, and bytes, by Ken Shirriff