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Blockchain 100 question 23
Publish: 2021-04-29 06:46:06
1. Do you want to learn blockchain development technology or just want to know what blockchain is? If it is the former, you can look at the code of other blockchain projects and learn about it first. If it is the latter, we can pay attention to some good blockchain we media. Blockchain is an emerging instry. There is no ready-made training course. It depends on self exploration and understanding.
3. One of the characteristics of blockchain projects (especially public chains) is open source. Through open source code, to improve the credibility of the project, so that more people can participate. But the open source code also makes it easier for attackers to attack blockchain system. In the past two years, there have been a number of hacker attacks. Recently, the anonymous currency verge (xvg) was attacked again. The attacker locked a vulnerability in the xvg code, which allowed malicious miners to add false timestamps on the block, and then quickly dig out new blocks. In a few hours, the attacker obtained nearly $1.75 million worth of digital currency. Although the subsequent attack was successfully stopped, no one can guarantee whether the attacker will attack again in the future
of course, blockchain developers can also take some measures
one is to use professional code audit services,
the other is to understand the security coding specifications and take preventive measures
the security of cryptographic algorithm
with the development of quantum computer, it will bring great security threat to the current cryptosystem. Blockchain mainly relies on elliptic curve public key encryption algorithm to generate digital signature for secure transactions. Currently, the most commonly used ECDSA, RSA, DSA, etc. can not withstand quantum attacks in theory, and there will be greater risks. More and more researchers begin to pay attention to cryptographic algorithms that can resist quantum attacks
of course, in addition to changing the algorithm, there is another way to improve the security:
refer to bitcoin's treatment of public key address to rece the potential risk of public key disclosure. As users, especially bitcoin users, the balance after each transaction is stored in a new address to ensure that the public key of the address where bitcoin funds are stored is not leaked
security of consensus mechanism
the current consensus mechanisms include proof of work (POW), proof of stake (POS), delegated proof of stake (dpos), practical Byzantine fault tolerance (pbft), etc
POW faces 51% attack. Because POW depends on computing power, when the attacker has the advantage of computing power, the probability of finding a new block will be greater than that of other nodes. At this time, the attacker has the ability to cancel the existing transaction. It should be noted that even in this case, the attacker can only modify his own transaction, but not the transaction of other users (the attacker does not have the private key of other users)
in POS, attackers can only attack successfully when they hold more than 51% of the token, which is more difficult than 51% of the computing power in pow
in pbft, when the malicious nodes are less than 1 / 3 of the total nodes, the system is secure. Generally speaking, any consensus mechanism has its own conditions. As an attacker, we also need to consider that once the attack is successful, the value of the system will return to zero. At this time, the attacker does not get any other valuable return except destruction
for the designers of blockchain projects, they should understand the advantages and disadvantages of each consensus mechanism, so as to select an appropriate consensus mechanism or design a new consensus mechanism according to the needs of the scene
security of smart contract
smart contract has the advantages of low operation cost and low risk of human intervention, but if there are problems in the design of smart contract, it may bring great losses. In June 2016, the Dao, the most popular funding project of Ethereum, was attacked. The hacker obtained more than 3.5 million Ethereum coins, which later led to the bifurcation of Ethereum into Eth and etc
there are two aspects of the proposed measures:
one is to audit the security of smart contracts, and the other is to follow the principles of smart contract security development
the security development principles of smart contract are: be prepared for possible errors to ensure that the code can correctly handle the bugs and vulnerabilities; Release smart contracts carefully, do well in function test and security test, and fully consider the boundary; Keep smart contracts simple; Pay attention to the threat intelligence of blockchain and check and update in time; Be clear about the characteristics of blockchain, such as calling external contracts carefully
security of digital wallet
there are three main security risks in digital wallet: first, design defects. At the end of 2014, a user lost hundreds of digital assets e to a serious random number problem (repeated r value). Second, the digital wallet contains malicious code. Third, the loss of assets caused by the loss or damage of computers and mobile phones
there are four main countermeasures:
one is to ensure the randomness of the private key
the second is to verify the hash value before software installation to ensure that the digital wallet software has not been tampered with
the third is to use cold wallets
the fourth is to back up the private key.
of course, blockchain developers can also take some measures
one is to use professional code audit services,
the other is to understand the security coding specifications and take preventive measures
the security of cryptographic algorithm
with the development of quantum computer, it will bring great security threat to the current cryptosystem. Blockchain mainly relies on elliptic curve public key encryption algorithm to generate digital signature for secure transactions. Currently, the most commonly used ECDSA, RSA, DSA, etc. can not withstand quantum attacks in theory, and there will be greater risks. More and more researchers begin to pay attention to cryptographic algorithms that can resist quantum attacks
of course, in addition to changing the algorithm, there is another way to improve the security:
refer to bitcoin's treatment of public key address to rece the potential risk of public key disclosure. As users, especially bitcoin users, the balance after each transaction is stored in a new address to ensure that the public key of the address where bitcoin funds are stored is not leaked
security of consensus mechanism
the current consensus mechanisms include proof of work (POW), proof of stake (POS), delegated proof of stake (dpos), practical Byzantine fault tolerance (pbft), etc
POW faces 51% attack. Because POW depends on computing power, when the attacker has the advantage of computing power, the probability of finding a new block will be greater than that of other nodes. At this time, the attacker has the ability to cancel the existing transaction. It should be noted that even in this case, the attacker can only modify his own transaction, but not the transaction of other users (the attacker does not have the private key of other users)
in POS, attackers can only attack successfully when they hold more than 51% of the token, which is more difficult than 51% of the computing power in pow
in pbft, when the malicious nodes are less than 1 / 3 of the total nodes, the system is secure. Generally speaking, any consensus mechanism has its own conditions. As an attacker, we also need to consider that once the attack is successful, the value of the system will return to zero. At this time, the attacker does not get any other valuable return except destruction
for the designers of blockchain projects, they should understand the advantages and disadvantages of each consensus mechanism, so as to select an appropriate consensus mechanism or design a new consensus mechanism according to the needs of the scene
security of smart contract
smart contract has the advantages of low operation cost and low risk of human intervention, but if there are problems in the design of smart contract, it may bring great losses. In June 2016, the Dao, the most popular funding project of Ethereum, was attacked. The hacker obtained more than 3.5 million Ethereum coins, which later led to the bifurcation of Ethereum into Eth and etc
there are two aspects of the proposed measures:
one is to audit the security of smart contracts, and the other is to follow the principles of smart contract security development
the security development principles of smart contract are: be prepared for possible errors to ensure that the code can correctly handle the bugs and vulnerabilities; Release smart contracts carefully, do well in function test and security test, and fully consider the boundary; Keep smart contracts simple; Pay attention to the threat intelligence of blockchain and check and update in time; Be clear about the characteristics of blockchain, such as calling external contracts carefully
security of digital wallet
there are three main security risks in digital wallet: first, design defects. At the end of 2014, a user lost hundreds of digital assets e to a serious random number problem (repeated r value). Second, the digital wallet contains malicious code. Third, the loss of assets caused by the loss or damage of computers and mobile phones
there are four main countermeasures:
one is to ensure the randomness of the private key
the second is to verify the hash value before software installation to ensure that the digital wallet software has not been tampered with
the third is to use cold wallets
the fourth is to back up the private key.
4. The bitcoin system can adjust the difficulty coefficient to ensure that bitcoin will not be g out too quickly
in order to ensure the stability of bitcoin and dig out a block in about 10 minutes, Nakamoto Tsung designed that the difficulty of getting bitcoin from miners mining should be dynamically adjusted every 2016 blocks (about 2 weeks). After the adjustment, the expected time for each block to be generated is 10 minutes. Now the difficulty factor is about 480ph / s. With the current computing power, the miners in the whole network need to go through about 300 trillion hash operations to find a qualified answer and generate new blocks.
in order to ensure the stability of bitcoin and dig out a block in about 10 minutes, Nakamoto Tsung designed that the difficulty of getting bitcoin from miners mining should be dynamically adjusted every 2016 blocks (about 2 weeks). After the adjustment, the expected time for each block to be generated is 10 minutes. Now the difficulty factor is about 480ph / s. With the current computing power, the miners in the whole network need to go through about 300 trillion hash operations to find a qualified answer and generate new blocks.
5. In Himalayas, Lao Wang talks about finance, which is easy to understand
6. At the beginning, I asked 100 questions about blockchain. The video explanation was very clear. After watching each episode, I would have a general understanding of blockchain. Now I will read some official account articles and block chain media websites, etc., to understand the daily information market. Some public official account has dry cargo, which teaches you all kinds of conceptual things, including the popular DAPP, and how to play and how to create wallet. You can go to see dappdiscover.
7.
Bitcoin (abbreviated as BTC) is a point-to-point, decentralized digital asset proposed by Nakamoto (alias); In 2009, Nakamoto Cong packaged the first block and won 50 bitcoin mining awards, which are halved every four years. According to this calculation, bitcoin is expected to be issued in 2140, with a total of 21 million
do you understand what bitcoin is now? If you don't understand, just continue to look down ~ "blockchain 100 questions" makes you a blockchain brick~
8. To put it simply, in the past, transactions were accounted by third-party platforms (Taobao, Jingdong, etc.), and blockchain kept a of this account book for each party (consumers, businesses, third-party platforms), so there was no way to go back on it, and there were more layers of protection
let's give an example. For example, in our usual online shopping, after placing an order, our money will be transferred to the intermediary platform of the third-party payment agency. After the seller delivers the goods and the buyer confirms the receipt of the goods, the buyer will inform the payment agency to transfer the money to the seller's account
however, the transaction mode supported by blockchain technology is different. Buyers and sellers can trade directly without any intermediary platform. After the transaction between the buyer and the seller, the system publishes the transaction information in the form of broadcast, and all hosts receiving the information record the transaction after confirming that the information is correct, which means that all hosts have done data backup for the transaction. If there is a problem with the orders proced by this machine, its data information will not be affected, because there are countless machines backing up data at the same time.
let's give an example. For example, in our usual online shopping, after placing an order, our money will be transferred to the intermediary platform of the third-party payment agency. After the seller delivers the goods and the buyer confirms the receipt of the goods, the buyer will inform the payment agency to transfer the money to the seller's account
however, the transaction mode supported by blockchain technology is different. Buyers and sellers can trade directly without any intermediary platform. After the transaction between the buyer and the seller, the system publishes the transaction information in the form of broadcast, and all hosts receiving the information record the transaction after confirming that the information is correct, which means that all hosts have done data backup for the transaction. If there is a problem with the orders proced by this machine, its data information will not be affected, because there are countless machines backing up data at the same time.
9. Aapxsr still has 9 times
come on, come on, come on
come on, come on, come on
10. Quantitative trading is the use of mathematics, statistics, information technology quantitative investment methods to manage the portfolio. In short, it can be divided into five steps: strategy conception, model establishment, data back testing, tuning back testing, and transaction following
stock quantitative investment model is mainly divided into two parts: risk model and multi factor stock selection model, which are used to control risk and improve returns respectively. Instry, market value and style factors are included in the risk model. The instry is not biased, market value is not biased, and style takes into account both long-term and short-term. Based on the risk model, the multi factor model covers seven categories of screening factors, including emotion, momentum, quality, valuation and other factors, as well as big data investment factors
indeed, to make a quantitative strategy, you must have a clear understanding of some basic indicators (factors). Take the fundamentals you mentioned, such as the price earnings ratio (PE). The higher the PE, the higher the valuation of the stock, and the higher the risk after buying; The lower the PE is, the more undervalued the stock valuation is and the greater the chance of rising after buying. Therefore, we can simply get a quantitative strategy of low PE, of course, this single factor strategy has great limitations, when we really do the strategy, we need to combine other factors, so that the back test results of the strategy will be more ideal, and the actual winning rate will be greater
if you are just an ordinary retail investor and want to adopt the quantitative trading system in future trading, it is necessary to learn it systematically.
stock quantitative investment model is mainly divided into two parts: risk model and multi factor stock selection model, which are used to control risk and improve returns respectively. Instry, market value and style factors are included in the risk model. The instry is not biased, market value is not biased, and style takes into account both long-term and short-term. Based on the risk model, the multi factor model covers seven categories of screening factors, including emotion, momentum, quality, valuation and other factors, as well as big data investment factors
indeed, to make a quantitative strategy, you must have a clear understanding of some basic indicators (factors). Take the fundamentals you mentioned, such as the price earnings ratio (PE). The higher the PE, the higher the valuation of the stock, and the higher the risk after buying; The lower the PE is, the more undervalued the stock valuation is and the greater the chance of rising after buying. Therefore, we can simply get a quantitative strategy of low PE, of course, this single factor strategy has great limitations, when we really do the strategy, we need to combine other factors, so that the back test results of the strategy will be more ideal, and the actual winning rate will be greater
if you are just an ordinary retail investor and want to adopt the quantitative trading system in future trading, it is necessary to learn it systematically.
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