Blockchain has great potential application value in international exchange, letter of credit, equity registration, stock exchange and other financial fields. The application of blockchain technology in the financial industry can save the third-party intermediary link, realize point-to-point direct docking, greatly reduce the cost and complete the transaction payment quickly.

For example, Visa launched Visa B2B Connect based on blockchain technology, which can provide institutions with lower cost, faster and safer cross-border payment methods to handle business-to-business transactions worldwide. You should know that traditional cross-border payment needs to wait 3-5 days and pay a transaction fee of 1-3%.

Visa also launched the first bitcoin debit card in cooperation with the Bitcoin base, and Citibank tested and operated the cryptocurrency "Citibank" in the blockchain.

2. Internet of Things and Logistics

Blockchain can also be naturally combined in the fields of Internet of Things and logistics. Through blockchain, logistics costs can be reduced, the production and delivery process of goods can be traced back, and the efficiency of supply chain management can be improved. This field is considered as a promising application direction of blockchain? [22]。

Blockchain can realize the comprehensive transmission of information in the whole network through the hierarchical structure of decentralized network connected by nodes, and can check the accuracy of information.

This feature improves the convenience and intelligence of Internet of Things transactions to a certain extent. The solution of blockchain+big data, using the automatic filtering mode of big data to establish credit resources in blockchain, can double improve the security of transactions and improve the convenience of Internet of Things transactions. Save time and cost for the application of intelligent logistics mode.

Blockchain points have very free access ability, and can independently participate in or leave the blockchain system without any interference to the whole blockchain system. The blockchain+big data solution takes advantage of the integration ability of big data, which makes the basic user expansion of the Internet of Things more directional and facilitates the user expansion among scattered users of intelligent logistics.

3. Public * * * service area

Blockchain is closely related to people's production and life in public management, energy, transportation and other fields, but the centralized nature of these fields has also brought some problems, which can be transformed by blockchain.

The decentralized and fully distributed DNS service provided by blockchain realizes the query and resolution of domain names through peer-to-peer data transmission services between nodes in the network, which can be used to ensure that the operating system and firmware of important infrastructure have not been tampered with, monitor the status and integrity of software, find bad tampering, and ensure that the data transmitted by systems using Internet of Things technology has not been tampered with.

4. The field of digital copyright

Through blockchain technology, works can be authenticated to prove the existence of works such as text, video and audio, and ensure the authenticity and uniqueness of ownership. After the work is confirmed in the blockchain, the subsequent transactions will be recorded in real time, realizing the whole life cycle management of digital rights, and can also be used as a technical guarantee in judicial evidence collection.

For example, Mine Labs, a startup in New York, USA, developed a metadata protocol based on blockchain. This system named Mediachain uses the IPFS file system to realize the copyright protection of digital works, mainly for digital pictures.

5. Insurance field

In terms of insurance claims, insurance institutions are responsible for fund collection, investment and claims settlement, and the management and operation costs are often high. Through the application of smart contract, the applicant does not need to apply, and the insurance company does not need to approve, but only needs to trigger the claim conditions to realize the automatic claim settlement of the policy.

A typical application case is LenderBot, which was launched by blockchain enterprises Stratumn, Deloitte and payment service provider Lemonway on 20 16. It allows people to chat through Facebook Messenger.

Register customized micro-insurance products to provide insurance for high-value items exchanged between individuals, and blockchain replaces the third-party role in loan contracts.

6. Public welfare field

The data stored in the blockchain is highly reliable and cannot be tampered with, so it is naturally suitable for social welfare scenarios. Relevant information in the process of public welfare, such as donation items, fundraising details, capital flow, feedback from recipients, etc. It can be stored in the blockchain, and it can be publicly and transparently publicized if conditions permit, which is convenient for social supervision.

structure

Blockchain is a decentralized, distributed and usually public digital ledger, which consists of records called blocks, and is used to record transactions on multiple computers, so any involved blocks cannot be changed retroactively, and all subsequent blocks will not be changed. This allows participants to independently and relatively inexpensively verify and audit transactions.

Use peer-to-peer network and distributed timestamp server to independently manage blockchain database. They are verified by large-scale collaboration driven by collective interests. This design improves stability? In workflow, participants have little uncertainty about data security. The use of blockchain eliminates the infinite repeatability of digital assets.

It confirms that each value unit is only transferred once, which solves the long-standing problem of repeated expenditure. Blockchain is described as a value exchange protocol. Blockchain can maintain ownership, because when properly set to specify the exchange protocol, it provides a record of compulsory offer and acceptance.

1 and block

A block contains many valid transactions, which are hashed and encoded into the Merkle tree. Each block contains the encrypted hash of the previous block in the blockchain, which connects the two. Linked blocks form a chain. This iterative process confirms the integrity of the previous block and returns to the original block, which is called the creation block.

Sometimes separate blocks can be generated at the same time, thus creating a temporary branch. Except for hash-based security history, any blockchain has a designated algorithm to score different versions of history, so that the version with higher score can be selected. Blocks that are not selected for inclusion in the chain are called orphans.

Peer computers that support databases sometimes have different versions of history. They only keep the highest sub-version of the database they know. Whenever a peer receives a high-scoring version (usually an old version with new blocks added), they will expand or overwrite their own database and retransmit the improved results to the peer. There is never an absolute guarantee that any particular project will always remain in the best version of history.

The construction of blockchain is usually to add the scores of new blocks to the old blocks and give rewards to expand the new blocks instead of covering the old blocks. Therefore, the probability of an item being replaced decreases exponentially as more blocks are built on it, and finally becomes very low.

Step 2 disperse

By storing data in its peer-to-peer network, blockchain eliminates many risks brought by centralized storage of data. Can a decentralized blockchain use ad hoc? Messaging and distributed networks. One risk of insufficient decentralization is the so-called "5 1% attack". In this case, the central entity can control more than half of the network and manipulate specific blockchain records at will, thus allowing double expenditure.

Peer-to-peer blockchain network lacks centralized vulnerabilities that computer hackers can exploit; Similarly, it has no central failure point. The blockchain security method includes using public key encryption. The public * * * key (a long, random expected digit string) is located at the address of the blockchain. The value token sent through the network is recorded as belonging to this address.

A private key is like enabling its owners to access their digital assets or otherwise interact with various functions. Blockchain now supports passwords. The data stored in the blockchain is generally considered to be indestructible.

Each node in a decentralized system has a copy of the blockchain. Data quality is maintained by large-scale database replication and computational trust. There is no centralized "official" copy, and no user is more "trusted" than other users.

Use software to broadcast transactions to the network. The news was delivered as best as possible. Mining nodes verify transactions, add them to the blocks under construction, and then broadcast the completed blocks to other nodes.

Blockchain uses various timestamp schemes, such as workload proof and serialized changes. Alternative methods of understanding include proof of equity. The growth of decentralized blockchain is accompanied by the concentration of risks, because computer resources need to process more data and become more expensive.

Step 3 make it public

An open blockchain is more convenient for users than some traditional ownership records. Although it is open to the public, it still needs physical access to view it. Since all early blockchains were unlicensed, the definition of blockchain is controversial. One of the questions in this ongoing debate is whether a private system that is under the responsibility of a central organization and authorizes (allows) inspectors should be regarded as a blockchain.

Proponents of license chain or private chain believe that the word "blockchain" can be applied to any data structure that processes data in batches into timestamp blocks. These blockchains are distributed versions (MVCC) of multi-version concurrency control in the database. Just as MVCC prevents two transactions from modifying a single object in the database at the same time, blockchain prevents two transactions from using the same single output in the blockchain.

Opponents say that the licensing system is similar to the traditional enterprise database, does not support decentralized data verification, and this system is not hardened against operator tampering and modification.

Nikolai Hampton of Computerworld said, "Many internal blockchain solutions are just cumbersome databases." "Without a clear security model, proprietary blockchain should be suspected."

Refer to the above? Baidu encyclopedia-blockchain