Knowledge points of blockchain exercises
hash
About Hash Hash is a term in computer science that means to input a string of arbitrary length and produce a fixed-length output. The hash value refers to the fixed-length output value obtained by calculating the input data of any length through the hash algorithm. The hash algorithm can not only be used for data encryption and verification, but also has a wide range of applications in blockchain technology.
Change any letter in the plaintext to get different hash values; hash algorithms include MD5, SHA and other algorithms; the length of the output value of the same hash algorithm is fixed; hash is a mathematical computer program
, It can accept input information of any length, and convert it into a fixed-length data fingerprint output form through a hash algorithm.
smart contract
A smart contract means that when a pre-programmed condition is triggered, the smart contract will immediately execute the corresponding contract terms.
The concept of smart contracts was first proposed by Nick Szabo in 1995; the blockchain using smart contracts can be applied in many aspects such as finance; the working principle of smart contracts is similar to the IF statement of computer programs.
blockchain system
The blockchain system is a decentralized distributed ledger technology, which is based on cryptography and peer-to-peer network technology, and has the characteristics of non-tampering, anti-counterfeiting, and transparency. The blockchain system consists of multiple nodes, each node can save and verify all transaction records, and maintain the security and consistency of the entire network through a consensus mechanism.
In the blockchain system, all transactions are packaged into a block, and the blocks are linked by cryptographic hashes to form an immutable and continuous blockchain. Each block contains the hash value of the previous block, thus forming an immutable chain of concatenated blocks. In this way, anyone can verify the transaction records in the blockchain, ensuring its authenticity and integrity.
The consensus mechanism in the blockchain system is the core mechanism to ensure the security and consistency of the blockchain. For example, the consensus mechanism used by Bitcoin is Proof of Work (PoW), the consensus mechanism used by Ethereum is Proof of Stake (PoS), and the consensus mechanism used by EOS is Delegated Proof of Stake (DPoS). The difference in the consensus mechanism will have an impact on the performance and security of the blockchain system.
The blockchain system can be applied in many fields, such as digital currency, supply chain finance, Internet of Things, etc. It can achieve decentralization, trust mechanism, transparency and other features, and provide safe and reliable solutions for various industries.
We can divide the blockchain system into four levels.
The first layer is the underlying protocol layer, also called "chain layer", which defines the basic data structure and encryption algorithm of the blockchain system, including block creation, transaction verification, consensus mechanism, etc.
The second layer is the "network layer", which handles communication between nodes, including message passing, network topology, data synchronization, and more.
The third layer is the "contract layer", which is responsible for the execution of smart contracts and realizes applications in different scenarios, such as digital currency, supply chain finance, identity authentication, etc.
The fourth layer is the "application layer", also called "DApp layer", which is built on smart contracts and provides specific application services, such as decentralized exchanges, crowdfunding platforms, game platforms, etc.
These four levels gradually provide the full functionality of the blockchain system from the bottom to the top. Different layers are supported by different technologies and standards. Among them, the chain layer is the most basic and the basis of other layers, while the application layer is the most intuitive and truly interacts with users.
knowledge points
1. Hyperledger is an alliance chain initiated by the Linux Foundation.
2. The key hash function of the blockchain seal plays a vital role in the blockchain. Its method is to encrypt and compress complicated transaction information into fixed words The simple hash value of the section becomes the identity of the block, ensuring that the transaction information in the blockchain is not tampered with.
3. The monopoly of data by individual companies means that data is not shared, forming a data island.
4. The main types of tokens should be payment tokens, usage tokens and proof of work tokens (Proof of Work Token).
5. The particularity of the blockchain itself enables it to realize the distributed accounting process in the application of related industries. It does not require any intermediary agencies to intervene and mainly complete transactions automatically through smart contract technology. 6. The distributed ledger can be said to be a
block The framework of the chain, everyone can freely participate in and jointly process the data in the blockchain. Based on this, the blockchain is actually a large distributed computing network. It does not have a central command to issue orders. The entire network is completely decentralized and requires different nodes to exchange information with each other to reach a consensus. Acting in unison, the whole process is like a group discussion without a leader. In this regard, some people have raised questions, what if some nodes send wrong information, interfere with the normal operation of the network, or everyone has a disagreement? Therefore, scholars have established a model to collectively refer to this type of problem as the Byzantine general problem.
7. The R3 blockchain alliance was established in September 2015, with members all over the world.
A. Zhongguancun Blockchain Industry Alliance: Managed by the People's Government of Haidian District, Beijing, the Blockchain Industry Alliance jointly established by many enterprises and institutions is committed to promoting the application of blockchain technology in various industries; B. Golden Chain
Alliance (Financial Blockchain Alliance): A blockchain industry alliance jointly initiated by China Financial Certification Center and a number of financial institutions, aiming to promote the application and innovation of blockchain technology in the financial field; C, R3 Blockchain Alliance
: Headquartered in New York, USA, it is a blockchain industry alliance co-sponsored by many banks and financial institutions around the world, focusing on the research and development of blockchain technology in the financial field;
D. Micro-Chain Alliance (Blockchain Microfinance Industry Alliance): A blockchain industry alliance jointly established by some Internet finance companies and blockchain companies, which is committed to applying blockchain technology to promote the development of the field of micro-credit.
8. On January 26, 2019, there are currently 10,246 Bitcoin full nodes in the world, and the number of full nodes located in the United States is the largest, accounting for 24.55%, while the number of full nodes in China ranks fifth, accounting for 4%
9 , The mining of the POW consensus mechanism requires a large number of hash operations, electricity and various computing power resources, and finding a suitable hash value actually has no other effect
. Service layer, core layer, base layer and management layer
11. The full name of DES is Data Encryption Standard, that is, data encryption standard, which is a block algorithm using key encryption. With the decryption key, "it is computationally infeasible to derive the decryption key from the known encryption key" cryptosystem MD5 Message-Digest Algorithm (English: MD5 Message-Digest Algorithm), a widely used cryptographic hash The function can generate a 128-bit (16-byte) hash value (hash value), which is used to ensure the integrity and consistency of information transmission. IPO: Initial Public Offering (Initial Public Offering) means that a company sells its shares to the public for the first time.
14. When building a risk control model, the indicators used for scorecard variable screening generally do not include any of the above 4 options A single as a filter indicator. These four indicators are mainly used to evaluate the predictive ability of the model and the importance of variables, and their meanings are as follows: AUC value and KS value are indicators for evaluating the quality of the model; IV (Information Value) value in Chinese means information value, which is an evaluation variable The index of predictive ability is used for variable screening; WOE is an index for discretizing the original variables.
A. KS value: It is one of the indicators used to evaluate the quality of the model. It is the absolute value of the difference between the horizontal and vertical coordinates of the point closest to the upper left corner on the ROC curve. The larger the KS value, the better the model effect.
B. IV value (information value): It is an index to measure the information expression ability of a variable. The higher the IV value, the more obvious the impact of the variable on the target variable, and the greater the importance.
C. AUC value: It is the ability of the model to identify positive and negative samples, and it is also one of the indicators for evaluating the quality of the model. The larger the AUC value, the better the model effect.
D. WOE value (weight coding): It is an index used to measure the importance of variables. The larger the WOE value, the greater the importance of the variable and the greater the impact on the target variable. There is a close relationship between it and the IV value.
15. DBFT (Delegated Byzantine Fault Tolerant) authorizes the Byzantine Fault Tolerant Algorithm
16. Ethereum's GHOST protocol does not consider orphaned blocks to be worthless, but rewards miners who find orphaned blocks. In Ethereum, orphan blocks are called "uncle blocks" and they can contribute to the security of the main chain.
17. The blockchain is based on the ledger with the highest block height, and the longest chain is based on the longest chain.
Nodes always think that the longest chain is the correct blockchain, and will continue to extend it. Miners are all mining on the longest chain, which is conducive to the uniqueness of the blockchain ledger.
If the Bitcoin transaction that transfers you money is not recorded on the longest chain, you may face financial loss.
Nodes always think that the longest chain is the correct blockchain and will continue to extend it, which is one of the foundations of the blockchain consensus mechanism. In the blockchain network maintained by nodes, there will be multiple branch chains, but in the end only the longest chain is considered correct because it has the most computational workload and the transactions on it are also considered to be the most reliable . Other branch chains will be abandoned and transactions in them will be invalid.
Miners are all mining on the longest chain, because miners will choose the longest chain for mining, because they can get higher rewards. If miners mine on non-longest chains, then they waste time and computing resources, because these mined blocks will eventually be discarded by other miners, and they will not receive any rewards.
If the bitcoin transaction that transfers you is not recorded on the longest chain, you may face financial loss. This is because Bitcoin transaction records are stored on the blockchain. If a transaction is not confirmed and added to the blockchain, there may be fraud such as double payment. If you have received this transaction, then you may suffer financial loss due to invalid bitcoins received. Therefore, when making a Bitcoin transaction, make sure that the transaction is confirmed and recorded on the longest blockchain.
18. Bitcoin blocks are generated every 10 minutes on average. This is the heartbeat of Bitcoin, the basis for the rate of currency issuance and the speed at which transactions are concluded. It must remain constant, not just in the short run, but over decades. During this time, computer performance will skyrocket. In addition, the people and computers involved in mining are constantly changing. In order for new blocks to be produced at a rate of one every 10 minutes, the difficulty of mining must be adjusted according to these changes. In fact, the difficulty is a dynamic parameter that is adjusted periodically to achieve the goal of a new block every 10 minutes. Simply put, the difficulty is set such that the rate at which new blocks are produced is maintained at 10 minutes regardless of mining capacity.
19. The core layer is the most important part of the blockchain system, which will affect the security and reliability of the entire system. Such as consensus mechanism, P2P network transmission, privacy protection;
20. The parties to the letter of credit mainly include the applicant, the issuing bank, and the beneficiary. 1. The issuing bank refers to the bank that opens the letter of credit at the request of the applicant, usually the bank where the importer is located. The issuing bank shall issue the letter of credit in a timely and correct manner according to the requirements of the applicant. The person who designates and accepts the letter of credit and collects the payment by invoice, bill of lading, etc., that is, the exporter.
21. The United States issued the Bank Secrecy Act in 2013. In August 2018, the Director of the Financial Crimes Enforcement Agency of the U.S. Department of the Treasury pointed out that regardless of whether the money transfer agency that can convert digital currency is in the United States or abroad, even if the foreign entity does not The establishment of entities in the United States must comply with the requirements of the Bank Secrecy Act (BSA) as long as their business is partially or completely related to the United States.