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Ethereum attacked

Publish: 2021-05-16 13:34:01
1.

a brief history of etheric Classics (etc)

etheric classics began with an unfortunate event

in May 2016, the decentralized autonomous organization (DAO) held a token sale with the goal of establishing a blockchain based venture capital to fund future decentralized applications (dapps) in the Ethereum ecosystem

basically, Dao is a complex smart contract that operates in a decentralized way - computer code that automatically performs tasks between multiple parties when conditions are met

despite its ambitious goals and successful token sales, Dao's code has a major vulnerability that allows attackers to steal eth from decentralized organizations

the attacker took advantage of this vulnerability in June 2016, triggering the infamous Dao hacking event, and maliciously stole eth worth about US $50 million

there is no doubt that Dao hacking has shocked Ethereum community and made eth price drop from $20 to $13

after the Dao hacking, the Ethereum community has to choose from three options

< UL >
  • do nothing and try to bear the consequences of the attack

  • start soft bifurcation to recover funds

  • deploy a hard fork to recover the lost eth

  • both soft and hard bifurcations are significant network upgrades. However, soft fork allows users who are not upgraded to communicate with upgraded users, while hard fork is not backward compatible with previous versions

    as developers realize that deploying soft forks will expose the network to distributed denial of service (DDoS) attacks, Ethereum community decides to initiate hard forks to recover the funds lost in Dao hacking attacks

    although this scheme is supported by most people, a small number of people in Ethereum community oppose it. They think that "code is the law" and blockchain network should be unchangeable

    the failure of both sides to reach an agreement on the solution eventually led to the fragmentation of Ethereum blockchain

    those who tried to recover the lost eth chose the hard fork and opened the Ethereum (ETH) blockchain as we know it today, while another group stayed on the original Ethereum classic (etc) chain

    what problems does ethereal classic solve

    Ethernet classic (etc) is a blockchain platform that allows developers to deploy smart contracts and dapps

    although this function is the same as Ethereum (ETH), etc blockchain has two main differences

    first of all, Ethereum classic community opposes tampering with distributed ledger and supports the view that "blockchain network cannot and should not be modified"

    secondly, although there is no rigid upper limit on the total supply of eth, it is allowed to create 230 million etc at most by adopting the monetary policy of constant supply

    as a bonus item, ethereal classic launched Atlantis hard bifurcation last year to increase the interaction with Ethereum and improve the privacy protection of transactions through ZK snarks

    the trading platforms recommended by ethereal classic etc are: Fire coin, okex, AAX, etc

    2.

    a brief history of etheric Classics (etc)

    etheric classics began with an unfortunate event

    in May 2016, the decentralized autonomous organization (DAO) held a token sale with the goal of establishing a blockchain based venture capital to fund future decentralized applications (dapps) in the Ethereum ecosystem

    basically, Dao is a complex smart contract that operates in a decentralized way - computer code that automatically performs tasks between multiple parties when conditions are met

    despite its ambitious goals and successful token sales, Dao's code has a major vulnerability that allows attackers to steal eth from decentralized organizations

    the attacker took advantage of this vulnerability in June 2016, triggering the infamous Dao hacking event, and maliciously stole eth worth about US $50 million

    there is no doubt that Dao hacking has shocked Ethereum community and made eth price drop from $20 to $13

    after the Dao hacking, the Ethereum community has to choose from three options

    < UL >
  • do nothing and try to bear the consequences of the attack; Or

  • start soft bifurcation to recover funds; Or

  • deploy a hard fork to recover the lost eth

  • both soft and hard bifurcations are significant network upgrades. However, soft fork allows users who are not upgraded to communicate with upgraded users, while hard fork is not backward compatible with previous versions

    as developers realize that deploying soft forks will expose the network to distributed denial of service (DDoS) attacks, Ethereum community decides to initiate hard forks to recover the funds lost in Dao hacking attacks

    although this scheme is supported by most people, a small number of people in Ethereum community oppose it. They think that "code is the law" and blockchain network should be unchangeable

    the failure of both sides to reach an agreement on the solution eventually led to the fragmentation of Ethereum blockchain

    those who tried to recover the lost eth chose the hard fork and opened the Ethereum (ETH) blockchain as we know it today, while another group stayed on the original Ethereum classic (etc) chain

    what problems does ethereal classic solve

    Ethernet classic (etc) is a blockchain platform that allows developers to deploy smart contracts and dapps

    although this function is the same as Ethereum (ETH), etc blockchain has two main differences

    first of all, Ethereum classic community opposes tampering with distributed ledger and supports the view that "blockchain network cannot and should not be modified"

    secondly, although there is no rigid upper limit on the total supply of eth, it is allowed to create 230 million etc at most by adopting the monetary policy of constant supply

    as a bonus item, ethereal classic launched Atlantis hard bifurcation last year to increase the interaction with Ethereum and improve the privacy protection of transactions through ZK snarks

    the trading platforms recommended by etc

    hot money, okex, AAX, etc

    3.

    There is an essential difference between Ethereum and bitcoin. What is the difference? Bitcoin defines a set of currency system, while Ethereum focuses on building a main chain (which can be understood as a road) to allow a large number of blockchain applications to run on this road

    from this point of view, Ethereum's application scenarios are more extensive, which is why we say that Ethereum marks a simple monetary system in the era of blockchain

    1.0, and a transformation to other instries and application scenarios in the era of blockchain 2.0

    however, there is no perfect thing in the world. Although Ethereum has expanded the application scope of blockchain in all walks of life and improved the speed of transaction processing, it also has some disputes and doubts

    first, the solution to the lack of scalability of Ethereum: slicing technology and lightning network

    the bottom design of Ethereum, the biggest problem is that Ethereum has only one chain and no side chain, which means that all programs have to run on this chain equally, consuming resources and causing system congestion. Just like last year's very popular Ethereum game "encryption cat", when this game was very popular, it once caused Ethereum network paralysis

    to improve the processing capacity, Ethereum proposes two ways: shard and lightning network. Let's introce these two technologies respectively

    (1) fragmentation technology

    vitalik buterin, founder of Ethereum, believes that the reason why mainstream blockchain networks such as bitcoin process transactions very slowly is that every miner has to process every transaction in the whole network, which is actually very inefficient. The idea of fragmentation technology is: a transaction does not need to be processed by all nodes in the whole network, as long as some nodes (miners) in the network are allowed to process it. Therefore, Ethereum network is divided into many pieces. At the same time, each piece can handle different transactions. In this way, the network performance will be greatly improved

    however, the slicing technology is also controversial. As we all know, the important idea of blockchain technology is decentralization. Only when the whole network witnesses (processes) the same transaction can it have the highest authority. The Ethereum slicing technology is similar to the group witness, not all nodes witness together. In this way, it will lose the absolute "decentralization" attribute, and can only achieve the purpose of high performance by sacrificing certain characteristics of decentralization

    (2) lightning network

    lightning network uses the way of transaction under the chain. What does that mean? It means: when the participants of lightning network transfer money to each other, they do not need to confirm the transaction through the main chain of Ethereum, but create a payment channel between the participants and complete it under the chain

    however, lightning network is not separated from the main chain. Before establishing a payment channel, you need to use the assets on the main chain as collateral to generate a balance proof, which indicates that you can transfer the corresponding balance. In the case that both parties of the transaction hold the balance certificate, both parties can make unlimited number of transfers under the chain through the payment channel

    only when the off chain transaction is completed and the assets need to be transferred back to the chain, the balance change information of the main chain account will be registered on the Ethereum main chain, and no matter how many transactions occur ring this period, there will be no record on the main chain

    another real benefit of lightning network is that it can save the cost of miners for you. At present, when we trade on the main chain of Ethereum, we need to consume gas and pay for miners. Once we move the transaction to the lower chain, we can save this part of the cost

    Of course, lightning network is not perfect. When using the lightning network, the assets on the main chain should be used as collateral; And this part of assets as collateral can not be used before the user completes the transaction under the chain. This also determines that lightning trading is only suitable for small transactions

    the above is the problem of insufficient scalability of Ethereum, as well as the two main solutions: fragmentation technology and lightning network

    Second, there are loopholes in Ethereum's smart contract and the infamous Dao event

    Ethereum's smart contract is very powerful, but there are loopholes in any code. The biggest controversy of Ethereum's smart contract lies in the so-called loopholes, that is, security issues. According to relevant research, 34200 (about 3%) of the nearly 1 million smart contracts based on Ethereum contain security vulnerabilities, which will allow hackers to steal eth, freeze assets or delete contracts, such as the infamous Dao incident

    (1) what does Dao mean

    before introcing the Dao event, let's first introce what Dao is. Dao is the abbreviation of decentralized

    autonomous organization, which can be understood as decentralized autonomous organization. From the perspective of Ethereum, Dao is a kind of contract or a combination of contracts on the blockchain, which is used to replace the government's review and complex intermediate proceres, so as to achieve an efficient and decentralized trust system. Therefore, Dao is not a specific organization, that is to say, there can be many Dao, all kinds of Dao

    (2) the infamous Dao event

    however, when we talk about Dao now, we basically refer to the Dao event, that is, the infamous hacker attack event we just mentioned. As we know, the English word "the" refers to "the Dao event". The Dao event

    refers to "the Dao event", because we just said that Dao is not a specific organization, there can be many Dao, all kinds of Dao

    in 2016, slock.it, a German company focusing on "smart locks", launched the Dao project on Ethereum in order to realize decentralized physical exchange (such as apartments and ships). Since April 30, 2016, the financing window has been open for 28 days

    unexpectedly, this Dao project is very popular. It raised more than US $100 million in just half a month. By the end of the whole financing period, it raised a total of US $150 million. Therefore, it has become the largest crowdfunding project in history. However, it didn't last long. In June, hackers took advantage of the loopholes in the smart contract to successfully transfer more than 3.6 million Ethernet coins and put them into a Dao sub organization, which has the same structure as the Dao. At that time, the price of Ethernet currency fell directly from more than $20 to less than $13

    this event shows that there are loopholes in smart contracts, and once the loopholes are exploited by hackers, the consequences will be very serious. This is why many people criticize Ethereum and say that its smart contract is not smart

    to solve this problem, many foreign companies begin to provide code audit services in order to solve the vulnerability problem of smart contract. From a technical point of view, some teams are currently testing smart contracts. Most of these teams are led by professors from Harvard, Stanford and Yale, and some of them have obtained investment from leading institutions

    in addition to the problems of insufficient expansibility and loopholes in smart contracts, the controversy over Ethereum lies in the POS consensus mechanism it pursues, that is, the proof of equity mechanism. Under the proof of equity mechanism, if anyone holds more money and holds it for a longer time, he will get more "rights" (interests) and have the opportunity to get bookkeeping power, Bookkeeping can also be rewarded. In this way, it is easy to create the oligarchic advantage of "the stronger the stronger"

    Another problem is the chaos of ICO. ICO is a common way to raise funds for blockchain projects, which we can understand as pre-sale. The outbreak of ICO projects on Ethereum has caused illegal activities such as fund allocation and money fraud under the banner of ICO, which has caused security risks to social and financial stability

    4. Ethereum blockchain has exposed three major problems, and its founder vitalik buterin has been unable to interpret them for a long time. The first is the low performance and TPS of Ethereum blockchain as a whole; The second is that resources are not isolated. The event of cryptokitties virtual cat once occupied 20% of the traffic of the whole Ethereum, which directly caused Ethereum network users unable to carry out timely transactions, which is the biggest pain point of resources not isolated; The third problem lies in the embodiment of Ethereum's governance structure. As a decentralized distributed ledger, the founder team of Ethereum has dominated its network development in the past. The over centralized governance mode has led to the bifurcation of eth, etc and ETF in Ethereum, and the Ethereum community is now in a state of fragmented governance. In the view of Ma Haobo, founder and CEO of "aelf", all kinds of disadvantages of Ethereum are unacceptable. Therefore, the positioning of "aelf" is born for the next generation of decentralized underlying computing platform of Ethereum, which focuses on solving the problems of insufficient performance, non isolation of resources and governance structure of Ethereum.
    5.

    The idea of Ethereum was born in 2013. Vitalik buterin ˙ When he was a programmer in the bitcoin community, he suggested to the core developers of bitcoin to develop a language for application developers to facilitate the development of various applications. Bitcoin core developers disagree. So God V decided to develop a new platform for this purpose

    V God wrote the white paper of etheric currency in 2013, in which he explained the goal of building a decentralized program. In 2014, we got development funds through crowdfunding, so we developed the Ethernet system< (better digital currency trading platform "currency exchange")

    since its birth, it has carried out four hard bifurcations so far

    for the first time, in order to adjust the difficulty

    released a stable version of "homeland" for the second time

    for the fourth time, in order to prevent DDoS and rece weight

    there is only the third hard fork, because of the hacker attack, and forced to fork. This is the Dao event

    On July 30, 2015, v-god and Ethereum Foundation created the first smart contract platform and designed the Dao Ethereum contract

    on April 30, 2016, the Dao smart contract was officially deployed, and the world's largest crowdfunding was completed, reaching an amazing $150 million As an aside, the biggest crowdfunding event in time is EOS crowdfunding, which has reached an even more amazing $5 billion!)

    on June 17, 2016, the Dao was attacked by hackers, who stole about 50 million US dollars of Ethernet currency, and the price also plummeted from US $20 to US $15, causing great harm to Ethereum. In order to recover the loss of investors, the community finally decided to hard fork

    therefore, on July 20, 2016, at the block height of 1920000, the hard branching was successful, and the new chain is called Ethereum eth, while the original chain is now Ethereum classic etc

    6.

    at present, the vast majority of digital currency transactions are concted in exchanges. Among the numerous exchanges, bitfinex, binance, okex and so on are well-known

    However, bitcoin and other digital currencies, as decentralized assets, have to be traded in a centralized exchange, which seems to have hidden contradictions and dangers

    1. Problems and challenges of stock exchanges=“ https://iknow-pic.cdn.bcebos.com/fd039245d688d43fdf16c83b761ed21b0ff43bbf ">

    in February 2014, Mt. GOx, the world's largest bitcoin exchange at that time, was stolen 850000 bitcoins, and the price of bitcoin suffered a" cliff "crash on that day. Later, it was revealed that Mt. GOx was in fact a thief, and only 7000 bitcoins were actually stolen

    in August 2016, bitfinex, the largest U.S. dollar bitcoin trading platform, suffered a security vulnerability, resulting in the theft of 120000 bitcoins, which was worth $65 million at that time. If converted into the price in December 2017, it would be worth nearly $2 billion

    on December 19, 2017, South Korea's youbit exchange was attacked by hackers and lost 4000 bitcoins, and the exchange declared bankruptcy

    on December 21, 2017, the Ukrainian liqui exchange was stolen 60000 bitcoins, and the unit price of bitcoin plummeted by US $2000

    in 2018, such a drama will only continue

    in addition to the threat of hackers, traditional exchanges also have some inherent shortcomings, such as lack of supervision and inefficiency. The security of the exchange for investors can only rely on its own credit, and the cost of running is very low. The stock exchange is regulated at the national level, but there is no such sword of Damocles on the top of the digital currency exchange. Moreover, in an exchange, the same order can only be submitted to one exchange. After the user places an order, the funds used for the transaction will be frozen and can only wait for the completion or cancellation of the transaction. These are undoubtedly inefficient

    All in all, the problems of exchanges are the problems of centralization

    2. Decentralization of exchanges=“ https://iknow-pic.cdn.bcebos.com/86d6277f9e2f070889a173c9e224b899a801f257 ">

    (1) the progress of the exchange itself

    the upgrade of security means is various. At present, the best use is cold wallet, that is, to keep the digital currency in the offline U disk. At the end of 2017, when the YouTube exchange was attacked, 75% of its assets were withdrawn into the cold purse in time to avoid greater losses. However, it seems to be a helpless way to protect the online assets by offline means. Of course, there should be many other methods, which will not be repeated here

    (2) the representative of cross ledger transaction is ripple network, and the operating company is ripple labs, which is a semi centralized system. Ripple is a decentralized clearing agreement. In order to solve the high cost and delay of inter-bank clearing, its base currency is XRP. Ripple network can connect all kinds of assets, such as US dollar, RMB, Japanese yen, bitcoin, etc. to its own network. In this system, U.S. dollars or bitcoin can be converted into reborn currency, and then reborn currency can circulate freely in the network, just as a highway is built between various assets. Due to the support of major banking institutions, the reborn currency achieved nearly 300 times growth in 2017

    (3) decentralized exchange

    some teams try to use blockchain technology to build a decentralized exchange. This kind of decentralized exchange, to some extent, is an extension of cross ledger trading

    bitshares is the most representative of early rising projects. It builds a blockchain development platform with servers scattered all over the world. Even if some of them are attacked, the system will not collapse. Anyone can transfer money and borrow money freely on this platform, and can also quickly build a centralized exchange based on this platform. In order to ensure stable value, bitstocks also require three times of digital assets as collateral. At present, bitstocks are running fairly well

    later, with the development of Ethereum and smart contract, the x x protocol came into being. This is an open protocol running in the Ethereum blockchain and a decentralized exchange in the Ethereum ecosystem. The agreement has attracted many investors. At present, it has completed financing and started to build open source software tools and infrastructure. Of course, there are many competitors. Ether Delta, IDEX and oasis DEX are trying to provide similar functions. Moreover, it is a smart contract system based on Ethereum, which only supports erc20 token. If other smart contract public chains start to rise, the demand will be reced

    in addition, there are some teams that are entering, such as the domestic road seal agreement, looping (LRC) in English. They adopted a design similar to the X protocol, and also introced a fast payment function similar to the lightning network. It is characterized by trying to match multiple exchanges, the user's order can be broadcast to multiple exchanges, and completed by different exchanges. Moreover, the user can still use the account funds after placing an order, and the user's behavior of transferring part or all of the funds is equivalent to partial or total cancellation. To some extent, it improves the breadth and timeliness of the transaction. However, this system seems to have damaged the "power" of the existing exchanges. Whether we can persuade everyone to play together will be a difficult problem

    At present, there is still a long way to go for the construction of decentralized exchange. In 3-5 years, traditional exchange will still be the main battlefield of digital currency

    However, in the future, it is worth looking forward to let the decentralized digital currency get rid of the shackles of centralization

    7. At present, there are many digital currency wallets, some of which have good personal experience

    light wallets are good for imtoken, geekwallet, kcash, Cobo, etc.

    Hardware wallets are good for ledger, trezor, etc., which involve large amount of digital currency or hold for a long time. Generally, hardware wallets are recommended

    big body introces these personal good light wallets

    1. Imtoken:

    is a mobile light wallet app, which supports Eth and Ethereum erc2.0 standard tokens (such as EOS, DGD, SNT, qtum)

    advantages: as Ethereum series light wallet, mtoken supports all the tokens of Ethereum erc2.0 standard, can control the miner's fee of each coin, can set the collection amount, and has convenient transaction record query, refreshing interface and easy operation, so it is suitable for ICO investors who need to receive a variety of erc2.0 standard tokens and trade infrequently

    disadvantages: 1. The "discovery" mole of the wallet is not intuitive enough. 2. The tokens that can only be stored on the Ethereum platform, such as BTC and Neo, can't be stored. At the same time, the bifurcations of bitcoin can't be stored

    2. Geek wallet

    geek wallet is a simple and convenient light wallet, which supports the storage and management of mainstream digital currency assets such as bitcoin (BTC), lightcoin (LTC), Ethereum (ETH), EOS, usdt, etc. Using bip44 mnemonics, local private key, off-line signature and other security mechanisms, as well as mobile phone and computer al backup strategy, completely solve the loss of digital currency assets caused by hacker attacks, virus infection, mobile phone loss, forgetting mnemonics and other ways, and provide users with online Multi Chain digital assets one-stop management service. The platform also has tiaoshao market, which can carry out token trading of physical assets on the chain

    advantages: it has high security factor, adopts local private key security mechanism, as well as mobile phone and computer al backup strategy, supports the current mainstream currency, and has a jump market on the platform, which can carry out token trading of physical assets on the chain

    disadvantages: usdt transaction must use 0.0001 BTC as transaction handling fee, does not support some small currencies, page optimization is good, but the function is relatively few

    3. Kcash

    kcash is also a light wallet. At present, it supports BTC, ETH, LTC, etc, act and digital currency based on Ethereum and achain smart contract platform. Kcash has cross chain and cross contract technology, and the supported currencies are still increasing

    advantages: as a Multi Chain Wallet, kcash supports multiple types of digital currencies and is very friendly to users who invest in multiple series of digital currencies. In addition, kcash also has the function of sending red packets, and in the future, it will launch currency transaction, bank card connection and other functions

    deficiency: too many features lead to poor usability. In addition, there are some compatibility problems with Android versions. Some Android models will flash back when opening apps< Cobo

    4. Cobo

    Cobo is a professional digital asset management wallet, which can help you store your assets safely. The unique POS gain can help you increase the value of your assets. It supports more than 20 kinds of digital assets including eth, EOS and TRX, as well as more than 500 kinds of tokens

    advantages: Cobo security is in the lead in the same level, using multiple security verification, hot and cold separation storage, HSM multi signature, Cobo provides you with stable income through intelligent voting, dpos vote pool, POS mining digital asset gain matrix

    disadvantages: poor page optimization, complex functions, a little difficult to get started, and there is also a flash back problem of Android version

    5. Ledger

    Hardware wallet, which supports eth, BTC, zcash and other mainstream currencies, uses encryption chip technology to build security solutions for users, and is used to protect users' digital assets and block chain application security. This is a hardware bitcoin wallet specially designed for consumers. It provides enterprise level security hardware moles and hardware procts supporting the Internet of things

    6, ledger

    Hardware wallet, support eth, BTC, zcash and other mainstream currencies; Using encryption chip technology to build security solutions for users to protect users' digital assets and block chain application security. This is a hardware bitcoin wallet specially designed for consumers. It provides enterprise level security hardware moles and hardware procts supporting the Internet of things.
    8. 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.
    9. How to earn money by raising cats
    on cryptokitties, you can buy virtual cats. By 17:00 Beijing time on December 6, 2017, the cheapest kitten had reached 0.037eth. Equivalent to 110 yuan per piece
    then the kittens have some opinions about the generation. For example, Gen 12 indicates that it is the 12th generation, while Gen 20 indicates that it is the 20th generation. Generally speaking, the smaller the algebra, the more valuable it is. And you can make your kittens slap each other. For example, a Gen 1 kitten and a Gen 1 kitten will give birth to a Gen 2 kitten
    you can sell your kittens and their offspring for money
    but what if you don't have two kittens? If you only buy one kitten, you can use your kitten to have fun with other people's high-quality kittens. The fee also depends on the kittens of your spouse (to be honest, this mechanism is very evil, similar to borrowing chickens to have children?) The quality of the proct. If your kitten is of high quality, you can also use your kitten to mate other people's kittens, and then you get Ethereum income
    but kittens also have special fertility rates
    every time a kitten gives birth to one generation, it will have a certain cooling time, ring which it can not regenerate kittens,
    the cooling time is divided into several grades
    fast: 1 minute
    swift: 2 – 5 minutes
    snappy: 10 – 30 minutes
    brisk: 1 – 2 minutes
    plodding: 4 – 8 minutes
    slow: 16 – 24 minutes
    sluggi Sh (lazy kitten): 2 – 4 days
    catatonic (nervous kitten): 1 week
    so the price of your cat also depends on its birth time
    and generally speaking, the larger the algebra is, the higher the gen value is, and the slower their growth rate is
    but I want to make complaints about it because CryptoKitties is too hot! Ethereum network has a little bit of a crash, the official recommended that every time you buy a cat, the minimum handling charge is 21000. 400000 fuel = 0.01eth. However, it is irritating that I raised the procere to 1.6 million fuel, which is 0.04, and Ethereum still failed. 0.04 Ethereum. That's more than 120 yuan. It's too dark.
    10. I don't know where the landlord said that he was attacked by hackers, but it's not impossible. Although blockchain is very popular at present, there is no absolute security for anything, even bitcoin
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