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Bitcoin attacked by double flower

Publish: 2021-05-16 12:24:30
1. 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
2.

I think the risk of buying bitcoin is very high, because the project test may fail in the future. Because the crash is used for capital. However, bitcoin itself is not a capital disk

first, bitcoin has been recognized by mainstream institutions

whether you believe it or not, this is an objective fact. Bitcoin has existed for 10 years and is getting better and better! The development of bitcoin in the past decade should be described as a sudden surge. Of course, there have been no less than 1000 reports of bitcoin's death in the past decade. However, the more bitcoin lives, the better, and those who believe in bitcoin will eventually get rich returns. At present, bitcoin has been launched on some mainstream exchanges, especially the Intercontinental Exchange and CME exchange in the United States. These two exchanges are the same as the Shanghai and Shenzhen exchanges in China. Of course, they are larger in scale. After all, they are global exchanges

of course, in addition to Ethereum, there are many projects that have done very well. I won't elaborate here. However, more projects are likely to return to zero in the future, because even Ethereum and bitcoin can not guarantee their success, let alone other projects. Therefore, if you want to invest in digital currency, it is recommended to be cautious, and then be cautious, and do not invest with funds that you cannot afford

3.

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=“ //www.yuanxue365.com/en/img_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=“ //www.yuanxue365.com/en/img_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

4. At present, there is an unpopular way to use bug to get your character into the wall, so that you won't be attacked by monsters, but you can't get out. If you insist on going to three-layer mining, the best way is to form a team to go down mining together
5.

Bitcoin is a kind of network virtual electronic currency, and its price has experienced roller coaster like ups and downs. It has no physical support, to put it bluntly, a string of computer code. Personally, I think this is a very unreliable thing. The Internet bubble is very big. In November 2013, the price of bitcoin once reached a high level of 8000 yuan / piece. Subsequently, the central bank, together with five ministries and commissions, issued the notice on preventing bitcoin risks, and the price of bitcoin plummeted. Now the price of bitcoin is more than 2300 yuan / piece

Jingxuan finance didn't you send a lot of articles a few days ago. China is now investigating bitcoin. Crash

6. 100m bandwidth has little to do with the connected computer
because the connected computers are controlled by the policy settings of the router
the most important thing is to allocate your bandwidth reasonably. In theory, if you download resources from a computer in your network segment, if your router does not allocate bandwidth, it may cause the computers in the whole network segment to get stuck on the Internet
if the distribution is reasonable and the router is powerful, then 200 computers can be easily handled.
7. The so-called 51% attack is to take advantage of bitcoin's ability to use computing power as a competitive condition to cancel the payment transactions that have already taken place

if someone has mastered more than 50% of the computing power, he can find the random number needed for mining blocks faster than others, so he actually has the absolute effective right of which block
he can:
1. Modify his own transaction records, which enables him to make double payments
2. Prevent the block from confirming some or all of the transactions
3. Prevent some or all of the miners from mining into any effective block
8. Let's say that the value of bitcoin is basically equal to the cost of mining, and the server cost is the rent of renting the server for one year. The bitcoin exchange rate is about $1000 a bitcoin. At present, 25 bitcoins are generated in 10 minutes, that is, about $25000 per 10 minutes, 150000 per hour, 3.6 million per day, and about $1.28 billion per year. If you want to maintain 51% of the computing power for one year, that is, you need to increase the computing power equivalent to $1.3 billion of server rent. If we want to maintain the short-term computing power, the price will not necessarily decrease a lot, because the price of short-term renting servers will be much higher. And the current mining machinery is basically ordered directly like the manufacturer, the actual cost is much lower than renting the server. Therefore, the cost of launching a 51% attack on bitcoin is not low
please accept if you are satisfied
9. Bitcoin, as a kind of P2P currency, is based on specific algorithms and a large number of calculations. Hacker attacks on bitcoin have not stopped since 2009. Hackers usually attack bitcoin trading platform, and then steal a lot of bitcoin, causing huge losses. So the general platform in the website protection have to work hard, just like before the domestic fire coin network used anti-D protection to ensure the safety of the website. Once attacked, the loss is unimaginable.
10.

According to a foreign media report on December 13, Beijing time, the world's largest bitcoin trading market, headquartered in Hong Kong,

"these bitcoin trading markets cross national boundaries, and there may be major transactions on systems and platforms outside the United States." "Without your knowledge, your investment funds may soon flow overseas," sec chairman Clayton said on Monday. As a result, this risk may be magnified, including that market regulators, such as the SEC, may not be able to effectively track down these bad actors or recover funds. "

this warning has at least been reflected to a certain extent in the bitcoin futures market. On Tuesday, the trading volume of bitcoin futures contract on CBOE futures exchange fell sharply, which is the second day of listing of the futures

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