Blockchain 6 times double flower

3.

The strict definition of blockchain refers to the distributed database technology that multiple nodes in peer-to-peer network jointly maintain a continuously growing list ledger constructed by time stamp and orderly record data blocks through consensus mechanism based on cryptography technology. This technical solution allows any number of nodes in the participating system to calculate and record all the information exchange data in the system in a period of time to a data block through cryptography algorithm, and generate the fingerprint of the data block for linking the next data block and checking. All participating nodes in the system jointly determine whether the record is true

blockchain is a technical solution similar to NoSQL (non relational database). It is not a specific technology, and can be implemented through many programming languages and architectures. There are many ways to realize blockchain, including pow (proof of work), POS (proof of stake), dpos (delegate proof of stake), etc

the concept of blockchain was first proposed in the paper "bitcoin: a peer-to-peer electronic cash system" by indivials (or groups) who call themselves Satoshi Nakamoto. Therefore, bitcoin can be regarded as the first application of blockchain in the field of financial payment

< H2 > [popular explanation]

no matter how big the system or how small the website is, there is a database behind it. So who will maintain this database? In general, who is responsible for the operation of the network or system, then who is responsible for the maintenance. If it is wechat database, it must be maintained by Tencent team, and Taobao database is maintained by Alibaba team. We must think that this way is natural, but blockchain technology is not

if we think of the database as a book, for example, Alipay is a typical account book. Any change of data is bookkeeping. We can think of database maintenance as a very simple way of accounting. In the world of blockchain, everyone in the blockchain system has the opportunity to participate in bookkeeping. The system will select the fastest and best bookkeeper in a period of time, maybe within ten seconds or ten minutes. The bookkeeper will record the changes of the database and the account book in a block. We can think of this block as a page. After the system confirms that the records are correct, the system will record the changes of the database and the account book in a block, It will link the fingerprint of the past account book to this paper, and then send this paper to everyone else in the whole system. Then, over and over again, the system will look for the next person with fast and good bookkeeping, and everyone else in the system will get a of the whole ledger. This means that everyone as like as two peas in the system is called Blockchain. It is also called distributed account technology. P>

as like as two peas (computer) have identical accounting books, and everyone has the same rights, they will not collapse e to the loss of contact or downtime of a single person. As like as two peas, the data is transparent and everyone can see what changes are in every account. Its very interesting feature is that the data can't be tampered with. Because the system will automatically compare, it will think that the same number of books with the largest number are real books, and a small number of books with different numbers are false books. In this case, it's meaningless for anyone to tamper with his own account book, because unless you can tamper with most nodes in the whole system. If there are only five or ten nodes in the whole system, it may be easy to do so. However, if there are tens of thousands or even hundreds of thousands of nodes and they are distributed in any corner of the Internet, unless someone can control most computers in the world, it is unlikely to tamper with such a large block chain

< H2 > [elements]

combined with the definition of blockchain, we think that we must have the following four elements to be called public blockchain technology. If we only have the first three elements, we will consider it as private blockchain Technology (private chain)

1, peer-to-peer network (power equivalence, physical point-to-point connection)

2, verifiable data structure (verifiable PKC system, non tampering database)

3, distributed consensus mechanism (Solving Byzantine general problem, solving double payment)

4 Game design of Nash equilibrium (cooperation is the strategy of evolutionary stability)

< H2 > [Characteristics]

combined with the definition of blockchain, blockchain will realize four main characteristics: decentralized, trustless, collective maintenance and reliable database. And the other two will be derived from the four characteristics  Features: open source  Privacy. If a system does not have these characteristics, it can not be regarded as an application based on blockchain technology

Decentralized: there is no centralized hardware or management organization in the whole network. The rights and obligations of any node are equal, and the damage or loss of any node will not affect the operation of the whole system. Therefore, it can also be considered that the blockchain system has excellent robustness

trustworthiness: there is no need to trust each other when participating in the data exchange between each node in the whole system. The operation rules of the whole system are open and transparent, and all data contents are also open. Therefore, within the specified rule range and time range of the system, nodes cannot and cannot cheat other nodes

collective maintenance: the data blocks in the system are maintained by all the nodes with maintenance function in the whole system, and these nodes with maintenance function can be participated by anyone

reliable database: the whole system will enable each participating node to obtain a of the complete database in the form of sub databases. Unless more than 51% of the nodes in the whole system can be controlled at the same time, the modification of the database on a single node is invalid, and the data content on other nodes cannot be affected. Therefore, the more nodes and computing power in the system, the higher the data security in the system

Open Source: since the operation rules of the whole system must be open and transparent, the whole system must be open source for the program

Privacy Protection: since there is no need to trust each other between nodes, there is no need to disclose the identity between nodes, and the privacy of each participating node in the system is protected

4. There are six hierarchical structures in the blockchain, which are from bottom to top: data layer, network layer, consensus layer, incentive layer, contract layer and application layer
1. Data layer
the data layer is the lowest layer in the six hierarchies of the blockchain. We can understand the data layer as a database, but for the blockchain, this database is a tamperable and distributed database, which is what we call "distributed ledger"
in the data layer, that is, the "distributed ledger", the data information on the blockchain is stored, and the blockchain structure, asymmetric encryption technology, hash algorithm and other technical means of the block are encapsulated to ensure the security of the data in the case of the whole network being open. The specific method is:
in the blockchain network, nodes use consensus algorithm to maintain the consistency of data layer (that is, the distributed database), and use asymmetric encryption and hash algorithm in cryptography to ensure the non usurpation and traceability of the distributed database
This constitutes the bottom data structure of blockchain technology. However, it is not enough to have a distributed database. We also need to let the data information in the database be shared and exchanged. Next, we will introce the upper layer of the data layer - the network layer
Second, network layer
the network system of blockchain is essentially a P2P (point-to-point) network. Point to point means that there is no need for an intermediate link or centralized server to control the system. All resources and services in the network are distributed in the hands of each node, and the transmission of information is also a direct communication between the two nodes. However, it should be noted that P2P
(peer-to-peer) was not invented by Nakamoto, and the blockchain only integrates this technology
therefore, the network layer of blockchain is actually a particularly powerful point-to-point network system. In this system, each node can not only proce information, but also receive information, just like sending e-mail. You can write your own e-mail, and you can also receive the e-mail sent to you by others
in the blockchain network, nodes need to jointly maintain the blockchain system. Every time a node creates a new block, it needs to notify other nodes in the form of broadcast. After receiving the information, other nodes verify the block, and then create a new block on the basis of the block. In this way, the whole network can jointly maintain and update the general ledger of the blockchain system
however, what rules should the whole network follow to maintain and update the general ledger of the blockchain system? This involves the so-called "laws and regulations" (rules), which we will introce next: the consensus layer
Third, consensus layer
in the world of blockchain, consensus simply means that the whole network should maintain and update the general ledger of blockchain system according to a unified and agreed rule, which is similar to the rule of updating data. It is one of the core technologies of blockchain and the governance mechanism of blockchain community to let highly dispersed nodes reach consensus efficiently in the decentralized blockchain network
at present, the mainstream consensus mechanism algorithms include: proof of work of bitcoin (POW), proof of rights and interests of Ethereum (POS), proof of rights and interests of EOS (dpos), etc
we now introce the data layer, network layer and consensus layer. These three layers ensure that there are data, networks and rules for updating data on the network. However, there is no free lunch in the world. How can nodes actively participate in the maintenance of the blockchain system? Here is the incentive layer, which we will introce next: incentive layer< 4. Incentive layer
incentive layer is the so-called mining mechanism, which can be understood as incentive mechanism: you can get as much reward as you contribute to the blockchain system. With this incentive mechanism, the whole network nodes can be encouraged to participate in the data recording and maintenance on the blockchain
mining mechanism and consensus mechanism are actually the same truth. Consensus mechanism can be understood as the company's general rules and regulations, while mining mechanism can be understood as the reward rules for what you do well in the general rules and regulations
just like the consensus mechanism POW of bitcoin, it stipulates that more work pays more. Whoever can find the correct hash value first can get a certain amount of bitcoin reward
and Ethereum's POS stipulates that the older the holder is, the more likely he or she will be rewarded
it should be noted that the incentive layer is generally only available for the public chain, because the public chain must rely on the nodes of the whole network to jointly maintain data, so there must be a set of incentive mechanism to encourage the nodes of the whole network to participate in the construction and maintenance of the blockchain system, so as to ensure the security and reliability of the blockchain system
the blockchain is safe and reliable, and it is not intelligent enough, right? The contract layer we will introce next can make the blockchain system more intelligent
v. contract layer
Contract layer mainly includes various scripts, codes, algorithm mechanisms and smart contracts, which is the basis of block chain programming. What we call "smart contract" is at the contract level
if the bitcoin system is not intelligent enough, the "smart contract" proposed by Ethereum can meet many application scenarios. The principle of the contract layer is to embed the code into the blockchain system, in this way to realize the smart contract that can be customized. In this way, on the blockchain system, once the terms of the smart contract are triggered, the system can automatically execute commands< Finally, the application layer. The application layer is very simple. As the name suggests, it is a variety of application scenarios and cases of blockchain. What we now call "blockchain +" is the so-called application layer. At present, the blockchain applications that have been implemented are mainly various blockchain applications built on
eth, EOS and other public chains. There are more applications of gambling and games, and the real practical applications have not yet appeared.

5. In the process of learning blockchain, you will hear the word "double flower", which means double payment, or more directly, a sum of money has been spent twice. In this article, we will briefly analyze why there are double flowers and how bitcoin can avoid double flowers

in the traditional transaction, there is no double spending problem because there is a centralized institution such as a bank: every payment will be dected from your bank account, and all details will be recorded in the bank. But in bitcoin, because there is no concept of account, utxo is introced, that is, no transaction output is spent. Because there is no guarantee from centralized institutions such as banks, when a transaction occurs, there may be a risk of double spending: for example, a has a bitcoin, and then he constructs two transactions T1 and T2 at the same time to spend the bitcoin, one of which is given to B, to buy a suit from B, one is given to C, and to buy a pair of shoes from C. If we do not introce some mechanism to avoid this situation, bitcoin, as a digital currency, will not have any meaning of existence. Next, let's analyze how bitcoin can prevent this "double flower" attack

(1) normal situation

first of all, let's look at the normal situation. To put it bluntly, most of the time, the consensus mechanism of blockchain can nip Shuanghua in the bud. Let's illustrate with the above examples:

suppose that a constructs two transactions T1 and T2, and transfers its own value of 1btc utxo to B and C respectively, in an attempt to obtain benefits from B and C at the same time. Then a broadcasts the two constructed transactions to the network almost at the same time

suppose that the miner node in the network receives the transaction T1 first, and finds that the source of funds for the transaction has not been spent, so it adds T1 to its own memory transaction pool and waits to be packaged into the block

in most cases, the miner node will receive transaction T2 soon. At this time, the miner node will refuse to process the transaction because the transaction input that T2 points to is the same as T1 that has been added to the transaction pool. Other miner nodes in the network are similar, so a's attempt to double flower is stillborn

(2) bifurcation

the above is normal, but there are also abnormal cases to consider: suppose that the miner nodes M1 and M2 dig out the block almost at the same time, and unfortunately M1 only receives transaction T1 when digging in the block, while M2 only receives transaction T2 when digging in the block, so transaction T1 and T2 are packed into two blocks respectively. Because these two blocks were g out at about the same time, resulting in the bifurcation of the blockchain:

some nodes in the network (which may be close to M1) received the block blk1 packed by M1 first, so they used the block to extend their own blockchain, while other nodes (which are close to M2) received the block blk2 packed by M2 first, and used the block to extend their own blockchain, So the whole blockchain network

6. Hello, of course.
blockchain is a new application mode of distributed data storage, point-to-point transmission, consensus mechanism, encryption algorithm and other computer technologies. Blockchain is an important concept of bitcoin. It is essentially a decentralized database. At the same time, as the underlying technology of bitcoin, it is a series of data blocks generated by using cryptographic methods. Each data block contains a batch of information about bitcoin network transactions, Used to verify the validity of its information (anti-counterfeiting) and generate the next block. In fact, the original English version of bitcoin white paper [1] does not use the word blockchain, but uses the word chain of blocks. In the earliest Chinese translation of bitcoin white paper [2], chain of blocks was translated into blockchain. This is the earliest time when the Chinese word "blockchain" appeared.

7. Because it comes from money. Virtual money is bought with real money. So it's also called coin there.

8. Tencent and Taobao have always been incompatible. But both of them are Internet giants in China and even in the world. Wechat blocked Taobao, and Ma Yun built his own contacts against wechat. WeChat's micro payment is also aimed at competing with Alipay. The pat Network was eventually sold to Jingdong, because competition was not Taobao. Taobao block QQ currency is also expected.

9. QQ coin is a kind of virtual currency issued by Tencent in order to facilitate users to purchase the virtual goods and services it provides. Its official price is: 1q coin = 1 yuan. However, if the amount of recharge is large, there will be a certain amount of discount on some recharge platforms
it should be noted that this is the recharge price. If it's selling q-coin, because q-coin recycling is now done by some third-party platforms, there will be a certain cost. Therefore, the recovery price of Q coin is generally lower than the recharge price, remember!

10. Digital currency will not be stolen in general. If you use a regular wallet and invest in a regular digital currency, there will be no problem!