How does the NTP clock server (satellite clock system) coordinate the integrated system?

NTP Clock server （ Satellite clock system ） How to coordinate the integrated system ？
NTP Clock server （ Satellite clock system ） How to coordinate the integrated system ？
This article mainly explains the important functions of blockchain ： Proof of work (Proof-of-Work). It mainly explains that the proof of work is an important feature for blockchain , And it's necessary ; Other features often mentioned in blockchain （ Such as security ） It's secondary , It's useful, but it's not necessary .

The explanation of this paper is mainly based on some interesting features of blockchain work proof , These characteristics can't be obvious , Sometimes it's even counter intuitive , For example, participants in the blockchain can solve problems together without communication .

After understanding these features , It should be easy for people to conclude ： Work proof is mainly to complete distributed or decentralized time mechanism （ Like a clock ）.

Please note that , This article is not about the proof of work itself , It just shows how blockchain uses it . If you don't know about proof of work , So this link might be a good start .

The time sequencing problem of decentralized ledger

Before further description and explanation , Let's focus on this first , That's the scheduling problem . A lot of the literature on proof of work is confusing , Because they always try to explain the result of the problem rather than first determine the problem itself .

Any ledger absolutely needs order . One cannot spend money that one has not received , You can't spend what you've already spent . Blockchain transactions （ Or blockchain transactions ） The order has to be clear , And there's no need for a trusted third party to coordinate the order .

Even if blockchain is not a ledger , It's just some sort of data like sequential logs , But for each node there is the same blockchain replica , Sequence is also necessary . Different order of blockchains means different blockchains .

however , If the transaction is generated by anonymous participants from all over the world , And there is no central organization responsible for the order of transactions , But the facts need to be sorted , So what to do ？ Although a deal （ Or block ） It might include a timestamp , But how credible are these timestamps ？

Time is just a human concept , A time scale, such as an atomic clock, is a “ A trusted third party ”. however , Due to the influence of network delay and time relativity , It is impossible to determine the sequence of events by time stamp in distributed system .

We are interested in “ Time ” It's not like we're used to years 、 month 、 The concept of day and other time . What we need is a mechanism , Through this mechanism, we can verify that one event occurs before another or may occur at the same time .（banq notes ： The sequence of events ）

First , For the concepts of what is before and what is after , Need to establish a point in time . Establishing a point in time at first seemed theoretically impossible , Because there's no technology accurate enough to measure Planck time . But as you can see , Bitcoin solves this problem by creating its own concept of time , At this point in time , It's actually possible to determine the exact point in time .

Leslie Lamport stay 1978 Year paper “ Time in Distributed Systems , Clock and sequence of events ” This problem is well described in , except “ A physical clock that is properly synchronized ” outside , This article does not actually provide a comprehensive solution . stay 1982 year ,Lamport It also describes “ General Byzantine question ”, and Satoshi In his first email, he explained how proof of work solved the problem , Because the bitcoin file says “ To implement a distributed timestamp server on a peer-to-peer network , We will need to use the proof of work system “, This shows that working proof is mainly to solve the problem of time stamp .

Time is fundamental

It must be emphasized that , In a distributed system, it is impossible to associate events with points in time , This is an unsolved problem , Until Nakamoto Tsung invented the blockchain work to prove this solution , A decentralized ledger is possible . There are many other technical details of blockchain , But timing is fundamental and important . No time, no blockchain .

Blockchain
Proof of work

In short , The work of blockchain has proved to be a system that meets certain requirements SHA-2 Hash value , This value is very difficult to find . The difficulty is that the hash is less than a specific number , The smaller the number is. , The rarer the input value is and the more difficult it is to find it .

It is called “ Proof of work ”, Because it's very rare to know a value with this hash , This means that finding such a value requires a lot of trial and error , namely “ Work ”. In turn, , It means “ Time ”.

By changing demand , We can change the difficulty , Thus changing the possibility of finding such hashes . The difficulty of bitcoin is adjusted dynamically , In order to find a correct hash every ten minutes on average .

Nothing happens between blocks

The state of a blockchain is represented by its blocks , Each new block produces a new state . The blockchain state moves forward one block at a time , And a block costs an average of 10 minute , This time is the minimum measure of blockchain time .

SHA No memory Memoryless, No progress Progress-Free

Secure hashing algorithm is memoryless in statistics and probability Memoryless. It's a particularly counterintuitive concept for us humans .

The best example of no memory is the toss of a coin . If a coin appears in succession 10 The same side , Does that mean the next throw is more likely to be the opposite ？ Our intuition says yes , But actually every throw is 50/50 The opportunity of , No matter how many coincidences happened before .

No memory for no progress Progress-Free it is desirable that . No process means , As miners try to solve the problem of iterating over random numbers to find the hash value of the next block （ Solution ）, Every attempt is a separate event , No matter how much work has been done in the past , The probability of finding a solution every time you try is constant . let me put it another way , In every attempt , None of the participants came closer to the solution or made any progress . A miner who has been looking for a hash for a year is no more likely to find a hash on the next try than a miner who has just opened a mine .

therefore , Find a given solution in a given period of time （ Hash value ） The probability of the hash is only determined by the speed at which all participants iterate in the hash . It's not history , Not the data , It's just the hash rate .

The hash rate is in turn a function of the number of participants and the speed of the device used to compute the hash .

SHA The input is irrelevant

In the bitcoin blockchain , The input is the block head . But if we just give it random values , So the probability of finding a consistent hash is still the same . Whether the input is a valid block or from / dev / random Bytes of , The average need is 10 Minutes to find the hash value of the next block .

Of course , If you find a hash that meets the requirements , But your input is not a valid block , Such a solution cannot be added to the blockchain , But it's still workload verification （ Though useless ）.

The difficulty is the galaxy

Strangely enough , Difficulties are universal , It means it's across the universe . We can get miners on Mars to help us find , They don't need to communicate with the earth miners , The key is every 10 It's only a few minutes before we find the answer .（ ok , They need to tell earth people in some way whether they have solved this problem , Otherwise we'll never know ）.

It is worth noting that , There is no real communication between distant participants , Because they work together to solve the same statistical problems , But they don't even know about each other .

such “ universality ” Although it looks amazing at first , But it's actually easy to explain . I use the “ Universal universal” The word" , Because it uses a word to describe it , But it does mean “ Every participant knows ”.

SHA-256 The input of can be considered as 0 To 2 Of 256 An integer between squares （ Because the output is 32 byte , in other words 0 and 2 Of 256 Square , Any larger value can guarantee that , For example, it becomes redundant ）. Even if it's very big （ Much larger than the number of atoms in the perceptible universe ）, It's a set of numbers , Every participant knows , Participants can only be selected from this set of data .

If the input set is well known , function （SHA-256） It is well known that , And the difficulty requirements are well known , So the possibility of finding a solution is really “ general ”.

Try SHA Will make you a participant

If the determined problem is to find a matching hash value , So you only need to try it once , and Bingo, You've also affected the global hash rate , And for the person who tries to be a participant in helping others solve problems . You don't have to tell people you did it （ Unless you really find a solution ）, Others don't need to know it , But your attempt did affect the results . For the whole universe ,no less.

If that's still questionable , A good analogy might be the problem of finding large prime numbers . It's hard to find the largest prime number , Once found , It becomes “ Was found to be ” or “ It is known that ”. There are countless prime numbers , But there is only one instance of every number in the universe . therefore , People trying to find the largest prime are working on the same problem . You don't have to tell anyone that you decided to look for the largest prime , You just need to post it when you find one . If no one finds the largest prime , Then it will never be found . therefore , As long as it turns out （ If found ） Be announced , Participate in （ Trying to find a ） person , Even if it's completely confidential , It still affects the results .

Think about this incredible statistic , That is to say, any participant will affect the result even in the case of complete confidentiality , Even if it doesn't succeed, it will , This is what makes Nakamoto's invention so brilliant .

It is worth noting that , Because of the search for SHA It's the concept of no progress , Every attempt can be thought of as a participant trying to join and leave immediately . therefore , Miners join and leave 50 times a second .

Participation is a statistical display

The global hash rate listed on many websites is not because every miner is in some “ Miner registration office ” register , They report hash rates regularly . But there is no such thing .

The hash rate is known , Because it's very important for 10 Find solutions to specific difficulties in minutes , On average, , Many of these attempts （ At the time of writing 〜10 Of 21） It has to be done by someone somewhere .

We don't know who these participants are , They never announced that they were working , People who don't find solutions （ In fact, they are all ） Didn't tell anyone they were working , Their location could be anywhere in the universe , But we know for sure that they exist . Because the problem needs to continue to be solved （ The hash value needs to be found ）.

Work is a clock

The key to the problem is ： The difficulty of finding a consistent hash is like a clock . If you like , A universal clock , Because there is only one such clock in the universe , So there's nothing to synchronize , Anyone can “ see ” it .

It doesn't matter that the clock isn't accurate . It is important to , It's the same clock for everyone , And the state of the blockchain can be unambiguously linked to the tick of the clock .

This clock is operated by multiple efficiencies of an unknown number of collective participants all over the world , Completely independent of each other .

The last part of the puzzle

The solution has to be a hash of the block （ The head of the block, to be exact ）. As we mentioned , Input doesn't matter , But if it's the actual block , So whenever a solution is found , It all happens at the tick of our working time check clock . Not before that , It's not after that , It's right at the moment of tick . We know this unequivocally , Because the block is part of the mechanism .

let me put it another way , If the block is not input to SHA256 function , We will still have a distributed clock , But we can't connect this block to the tick of this clock . Using blocks as input solves this problem .

It is worth noting that , Our work proves that the clock only provides us with tick timing . There's no way to judge the order from tick to tick , This is it. Merkle The use of trees .

How about distributed consensus ？

Consensus means agreement . All participants can only agree on the tick of the clock, and have no choice but to reach a consensus . Besides , Everyone knows the tick and the additional data . in fact , As Nakamoto explained in the email quoted earlier , This really solved the Byzantine general problem .

In a rare but common case , There are two consecutive ticks associated with a block , conflict . This conflict is resolved by what block is associated with the next tick , Make one of the controversial pieces “ orphan ”. How blockchain continues is an accident , So it can also be indirectly attributed to the working time clock .

this is it

This is what work has been done for blockchain . This is not a “ The miners ”, Miners have the right to solve problems , It's not about turning real energy into a valuable concept , It's all the red herring .

for example , The reward of winning the prize is the reason to encourage miners to participate , But that's not what makes blockchain possible . Block is a Merkle Trees , But it has nothing to do with proof of work , It encrypts the block sorting record .Merkle The tree also makes the former tick “ More sure ”,“ There is no denying that ” Or simpler .

Workload proof is also a mechanism that blocks are actually immutable , It's a good side effect , Can make it possible to isolate witnesses , But it can also be done by retaining the signature （ Witness ） To complete , So it's secondary .

Conclusion

The work of bitcoin blockchain proves to be just a distributed 、 Distributed clocks .

If you understand the explanation , So you should better grasp the proof of work and the proof of rights and interests Proof-of-Stake Comparison , And obviously the two are not comparable ： Proof of interest is about （ Randomly distributed ） jurisdiction , And the work proved to be a clock .

In the context of blockchain , Proof of work can be a misuse . The term is Hashcash The legacy of the project , It's really used to prove work . In blockchain , But it's mainly about time spent verifiably . When people find a hash value that satisfies the difficulty , People find it takes time . The way to complete this time is “ Work ”, Hashing is interesting , Because it's a proof of time .

The fact that work proves to be all about time and not work also shows that , There may be other similar statistical challenges , These challenges take time and effort . This may also mean that the bitcoin hash rate is too high , And the bitcoin clock we described above can run reliably at a fraction of the hash rate , But hash rate is an incentive structure to stimulate energy consumption .