https://www.zhihu.com/question/37290469
Link: https://www.zhihu.com/question/37290469/answer/107612456
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Here's the thing, recently my roommate Hasaki has been asking me about blockchain and bitcoin. I tried a lot of different postures to explain to him what blockchain technology is in a simple and vivid way, but in the end both failed. So I came up with the idea of writing a BlockChain for Babies (aka: How to explain the blockchain to your mentally handicapped roommate), in order to be simple, intuitive and vivid to the people who don't understand blockchain technology but want to know about the block chain. What is the chain of people who introduce blockchain technology or bitcoin.
Because it is aimed at readers who do not want to know the specific technical implementation and only want to understand the blockchain, this article avoids some underlying and algorithm details, and adopts a more subjective way to show the author's perceptual understanding of blockchain technology. If you're just interested in blockchain and don't plan to study it in depth, or just want to act like me when others ask, this article should be a good "introduction".
Overview
A blockchain is essentially a decentralized distributed ledger database (thanks
Note: This term may be used in Bitcoin-related blockchain applications, but blockchain technology may not include a "ledger"). It itself is a series of data blocks generated using cryptographic associations, and each data block contains information that multiple Bitcoin network transactions are validly confirmed.This is the definition of blockchain, so to understand blockchain step by step, we need to understand the following things step by step.
decentralization
Let's first consider a process of centralized centralized processing. You want to buy a mobile phone on a certain treasure. The transaction process is: you send the money to Alipay - after Alipay collects the payment, notify the seller to deliver the goods - the seller delivers the goods - you confirm the receipt - Alipay sends the money to the seller.
Figure 1: Centralized centralized exchange model
In this process, although you are dealing with the seller, the transaction also involves a third party besides you and the seller, namely Alipay. The transaction between you and the seller is all about Alipay. Therefore, if there is a problem with the Alipay system, the transaction will fail. And even though you simply bought a phone, you and the seller have to provide redundant information to third parties. So consider extreme cases, if Alipay runs away or takes the money but does not recognize your transaction or the city where Alipay is located drives everyone away because of the G20 (?), then you are in a tragedy.
The decentralized method is much simpler. You only need to exchange money and mobile phones with the seller, and then both parties claim to have completed the transaction, and it’s OK.
It can be seen that in some specific cases, the decentralized processing method will be more convenient, and at the same time, there is no need to worry about the leakage of information unrelated to the transaction.
In fact, if only two people's transactions are considered, the benefits of decentralization cannot be fully demonstrated. It is assumed that if there are thousands of transactions in progress, the decentralized processing method will save a lot of resources and make the entire transaction autonomous and simple. and eliminates the risk of being controlled by a centralized agent.
Decentralization is a subversive feature of blockchain technology. It does not require a centralized agent and realizes a point-to-point direct interaction, making the information exchange method of high efficiency, large-scale, and decentralized agents a reality.
Of course, the above example has a big potential problem: without an authoritative centralized agent, how to ensure the accuracy and validity of each transaction? For example: If there is no authoritative centralized agent, what should I do if Zhang San lent me 100 yuan one day, but he doesn't pay back the money and doesn't admit it? Here are other features of the blockchain.
Two basic puzzles
After decentralization, there is no authoritative centralized agent in the entire system, and the credibility and accuracy of information will face problems.
Question 1: Quasi-two-army problem
The first time I heard about this problem was in the TCP class. It was roughly said that there were two armies far apart to pass information. The Red Army sent a messenger to the Blue Army and said: "You goddamn take the Italian guns. come out!". After receiving the information, the Blue Army sent another courier to the Red Army to say: "Instructions received!". Then the Red Army sent another messenger to the Blue Army and said: "I know you have received orders!". Then the Blues sent another messenger to the Reds and said: "I know you know I have orders!". Then the Red Army sent another messenger to the Blue Army and said, "I know you know I know you have orders!"...and it was endless.
Figure 2: Consistency on asynchronous systems and unreliable channels is impossible in distributed computing
In this case, because it is point-to-point communication, it is impossible for both parties to achieve information consistency in this case. Strictly speaking, it is "in distributed computing, trying to achieve consistency on asynchronous systems and unreliable channels is impossible".
Problem 2: Byzantine Generals Problem
In the military operations of the Byzantine Roman Empire, the strategy of general voting was adopted to decide whether to attack or retreat, that is to say, if the majority decided to attack, they would go up and do it. But if there are spies in the army (for example, the general has deliberately voted indiscriminately against the water, or the messenger has defected and modified the military order without authorization), how can we ensure that the final vote really reflects the will of the loyal general?
The Byzantine generals problem is reflected in the field of information exchange. It can be understood that in a decentralized system, some nodes are broken, and they may broadcast wrong information to the outside world or not broadcast information. In this case, how to verify Accuracy of Data Transmission.
The birth of blockchain technology
Now let's solve these problems step by step in a decentralized system and witness the birth of the prototype of blockchain technology.
1
Let's build a decentralized system first. For the convenience of understanding, let's look at a simple decentralized lending model: if A borrows B 100 yuan, at this time, A shouts in the crowd "I am A, I lent B 100 yuan!", B also shouted in the crowd "I am B, A lent me 100 yuan!" At this time, passers-by A, B, C, and D all heard the news, so everyone was in In my heart, I silently wrote down "A lent B100 yuan". You see, at this time, a decentralized system is established. This system does not require banks, nor does it require loan agreements and receipts. Strictly speaking, it does not even require a long-term trust relationship between people (for example, B suddenly Change your mouth and say "I don't owe A money!" At this time, the people will stand up and say "No, my small book records that you borrowed A100 yuan one day!").
Figure 3: Decentralized Lending Model
2
You may have discovered that in the above model, the so-called "100 yuan" is no longer important. In other words, anything can be exchanged in this model, and even you can make up something out of thin air, as long as everyone admits it, you can let the thing you make up circulate. For example: I shouted "I created 10 chakras!" in a crowd, I don't even need to know what a chakra is, and I don't need to care if there really is a chakra in the world, as long as everyone hears it, and then Write down "LaiW3n has 10 chakras" in my notebook, so I really have 100 chakras. From now on, I can claim that I gave someone 1 chakra, and as long as passers-by A, B, C, and D all receive and acknowledge this information, then I will complete the transaction, even if there is no chakra in the world.
Have three words popped into your mind right now - "Bitcoin"? Since the real blockchain and Bitcoin are much more complicated and detailed than the model I mentioned above, the following is an example of Chakra. After all, this article is Blockchain for Babies. (laughs)
3
Suppose that after a long time, the chakra I created out of thin air has been circulated in this system, and everyone has begun to recognize the chakra. But there are only 10 chakras in this system, so someone has a bad idea. He shouted "I have 10 chakras!" in the crowd. What should I do? Did everyone directly record in the notebook that he has 10 chakras, so that everyone can forge chakras?
To prevent this from happening, I decided to tag my chakras when I create them (more precisely, I tag the phrase "I created 10 chakras" when I shout, like Mark it as 001), so that in the future, when I shout "I gave so-and-so a chakra!" in each transaction, I will add an extra sentence: "The source of this 1 chakra! It is the record marked as 001, and this sentence of mine is marked as 002!". Let's abstract it a little more, and the format of the content of someone's shouting becomes: "This sentence is numbered xxx, the number of the previous sentence is yyy, I gave a chakra to so-and-so!", which solves the forgery question. In fact, the above model becomes a simplified Satoshi Nakamoto first version of the Bitcoin blockchain protocol:
Figure 4: Comparison of Chakra Model and Satoshi Nakamoto's First Edition Blockchain Protocol
Well, here you are basically able to explain the blockchain to your mentally handicapped roommate vividly and without any details. But maybe your roommate is a student with the spirit of breaking the casserole, so you'd better continue to answer the following questions.
1. "Why?"
Your roommate may ask: "Why do you call me a word and I will remember it for you? Don't I need money for my small book?". In order to motivate everyone to help me with my words and bookkeeping, I decided to give some rewards to the first person to hear my words and record them in the notebook: the first person to hear my words and record them, you will get 1 out of thin air. A chakra, this chakra is the reward for the whole system to keep your account, and after you record this sentence, you should immediately tell others that you have recorded it, ask others to give up and continue to record this sentence, and give Your own record number allows others to check, and then you shout out my words plus your record number for the next person to keep accounts.
When this rule is set, there will definitely be a group of people in this system, who will start to listen to the sounds around them with their ears erect, in order to seize the right to be the first to book. Yes, did the word "Bitcoin mining" pop up in your mind again?
It is worth mentioning that with regard to Bitcoin mining,
A very vivid example is given:Single Wangs are looking for female votes. The national mother-in-law said that I have many daughters, so let me give you some questions, and I will give one of the girls' WeChat accounts.
Singles compete wildly, trying to break their heads to solve problems. As long as one of the wangs solves a problem, he will immediately tell the world proudly that all the demonstrators are single, this girl is mine, you give up. Even if the other singles are dissatisfied, there is nothing they can do, and it is not a problem to be melancholy and annoyed. Let’s go to the next problem immediately. After being recognized by her mother-in-law, this lucky little wang who likes to win the girl can also get a betrothal gift of 25 currency units, which is a winner in life.
2. "Listen to whom?"
In this system, if I and another person C shout out at about the same time: "For Azeroth!". Due to the different positions of the audience, some people will hear the sentence I said first, while others will hear the sentence C first. If we stipulate that only one person can say this sentence, then in the end Who said this?
If no conditions are added, the above situation must develop like this: some people think that this sentence is said by me, and after hearing this sentence, they start accounting, and everything they do after that is based on this fact, And as this information is passed on again and again, the information chain will get deeper and deeper; and another group of people who think that C said this sentence first will also develop according to this trend. In this way, what was originally a single chain of information forked after we shouted the words "for Azeroth"! ?
Figure 5: "Blockchain" forks
What will this lead to? According to our assumption, the things recorded in everyone's notebook should be the same, and it should be a chain that can connect all the information. But at this moment, the things recorded in their notebooks are different! Is this still playful? How to determine the authenticity of transactions and information in the future! ?
In order to solve this problem, I have added a new rule: everyone needs to take off their shoes and hold a pen with their feet when recording the notebook, and write in block italics on the notebook! With this rule, it takes at least 10 minutes for each person to finish writing due to the difficulty of writing with their feet. Moreover, because everyone has different proficiency in writing with their feet, the time it takes to write this sentence is also different, so there must be someone. Write first and then shout "I'm done! That sentence was shouted by LaiW3n!", so that others who are writing this sentence will stop and start again in the small notebook "That sentence is the communication Written, the number of the previous sentence is xxx".
If you are interested in my solution above, you can understand the following knowledge according to my analogy above:
"Who to listen to" - Satoshi Nakamoto's algorithm for cracking the "Byzantine Generals Problem"
"Record in a small book" - Bitcoin mining
"Take off your shoes and write with your feet" - Bitcoin mining difficulty
"Shoes off writing speed" - computing power
"New Rules" - Proof of Work Chains
3. The "double spend" problem
At this time, your roommate may ask again: If I announce at the same time that I gave A a chakra and I gave B a chakra, but I only have one chakra, what should I do? Did both A and B receive chakra or what?
At this time, you only need to hold his chin, look into his eyes tenderly, scratch his nose with your hand, and say, "Little goblin, you bring this situation to the above rules and try it?"
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Some private message discussions:
1. Why are there still few cases of the connection between blockchain and physical business?
Theoretically: Blockchain is a new technology. The conservative public (including me) is still in the wait-and-see stage. Only a few radical or well-targeted entities have begun to march into the blockchain, and these few entities are speaking out at this stage. The strength is not enough.
In terms of application: the blockchain technology needs to be further developed in terms of technology and rules in order to connect with the entity business. The so-called "distrust" problem solved by the blockchain is limited to the data on the blockchain. Therefore, if the blockchain is to be connected with the entity business, it is necessary to further promote the establishment of cross-domain "rules of the game" between entities and data.
2. Will virtual cryptocurrencies eventually lead to Ponzi schemes?
I'm not very good at answering this question, after all, I am a technical person rather than a trendsetter in this field. My personal opinion is: For ordinary people, it is not recommended to hold a certain digital currency for a long time, and the digital currency should be used as a bridge for the conversion between legal currencies; within the acceptable range. PS: Actually I don't really care about this issue.
3. Why do I feel that the blockchain is mentally retarded after listening to you?
I have explained in the article that this is just an introduction to blockchain technology for newcomers, its purpose is to help you quickly have a perceptual understanding of blockchain; if you really want to know the details of blockchain technology, please read the relevant literature Or visit the blockchain community.
4. Job opportunities
Thank you for your enthusiastic HR, but I have no plans to change jobs at the moment.
5. Reprint
Individuals can reprint, please indicate the source and let me know; for commercial organizations or for commercial purposes, please send a private message.
A blockchain is a permanent, irreversibly modified record generated by superimposing (chain) encrypted data (blocks) in chronological order.
Imagine a closed island real estate market where only islanders are allowed to buy and sell island homes; all transaction records are printed and kept by the island's only real estate agent (because no one else has a printer). The property transaction record of each house is an information chain; the information of each past transaction of the house forms a chain in chronological order. Suppose each record is locked in a separate mailbox, and only the owner of the house has the key; new transaction records can be stuffed into the mailbox and become the latest link in the chain of information, but once in the mailbox, the record will be lost. It can be taken out and discarded again, or modified.
At this point, the combination of all these mailboxes is a non-digital blockchain - information encryption, each key holder can only see or authorize others to see the transaction information of his own house; and each time a transaction is added to the house Information is a permanent and irreversible process. It is not lost and cannot be modified.
Imagine again: If there is no intermediary on the island, but each family has a printer and a mailbox wall corresponding to all the properties on the island, each family can still only open the mailboxes on the wall related to their own properties. If every time a house is traded, the trader will go to all the houses on the island and add a page of records to the corresponding mailbox. At that time, even if a fire broke out in a few houses and the transaction records were lost, or someone secretly deleted the records in their mailboxes, the overall transaction records would not be biased - residents only need to take out each transaction before each transaction. Individuals keep copies of transaction records, determine a unified transaction history based on the principle of majority, and correct erroneous copies, allowing the blockchain to run unsupervised. This is another technology that is often confused with blockchain: distributed ledgers.
Blockchain is a technology that can completely change the underlying design of the financial system, because it can achieve indiscriminate records of ownership and transaction records of all market participants for all assets in the market, so it can completely eliminate liquidation and custody before transactions. The intermediate link of ownership confirmation after middle school; in addition, as an electronic information record, the blockchain can be combined with computer algorithms to automate transactions, that is, smart contracts. There are many derivative applications of blockchain combined with other financial technologies, each of which can replace a type of market intermediary. Blockchain is to financial services what TCP/IP is to the Internet: once the underlying standards are recognized and popularized, specific applications like Bitcoin and R3 will appear in every corner of financial services.