Double effect of digital currency
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
China's digital currency is as long as there is a mobile phone, no network, as long as the touch can be paid, and with detailed transaction records, it is very helpful to combat money laundering crime; This currency is mainly aimed at grabbing shares for Alipay, WeChat and POS terminals. It can also pave the way for RMB internationalization. Digital currency is not only safe and endorsed by the state, but the global central bank is pushing digital money. Now the digital currency is still in the testing stage. What time will it be popularized? It will have to wait until the Beijing Winter Olympic Games in February 2022 to fully promote the use
China's central bank's digital currency can be used for daily micro payments. Because it will be more stable with the endorsement of the state, the central bank's digital currency is different from bitcoin and Libra launched by Facebook. I give digital currency legal effect, and indivials can't refuse to accept it. At the same time, it is very convenient to use. It can be paid without binding any bank account. Digital currency will not cause inflation. Now it can be implemented and used in Shenzhen, xiong'an, Cheng, Suzhou and other cities. It also shows that the era of paperless is coming. Digital currency is a new concept with high technology content. In the future, RMB will enter the 3.0 era. Although the current digital currency is more powerful, it is still unable to put an end to money laundering and corruption
it is obvious that Byzantine error is the model of excessively pessimistic, because this kind of error is relatively rare in the actual environment. So why study this model? One of the simplest reasons is that if a consistency algorithm can ensure that the system is consistent when f Byzantine errors occur in the system, then this algorithm can also ensure that the system is consistent when f other errors occur
If an error model has an upper limit, it must have a lower limit (there is no model weaker than it). This lower bound is the "fail stop" model. The assumption of this model is: when a node fails, the node will stop running, and all other nodes know that the node has an error. Using the same logic, if a consistency algorithm can't guarantee consistency when f errors occur in the system, then the algorithm can't deal with other F problems
using these error models, we can compare different algorithms and discuss the cost of specific algorithms.