Bitcoin - Proof of work
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- čas přidán 30. 04. 2013
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An explanation of cryptographic proof-of-work protocols, which are used in various cryptographic applications and in bitcoin mining.
More free lessons at: www.khanacademy.org/video?v=9V...
Video by Zulfikar Ramzan. Zulfikar Ramzan is a world-leading expert in computer security and cryptography and is currently the Chief Scientist at Sourcefire. He received his Ph.D. in computer science from MIT.
It's still possible to hear bits of what is being said. You should speak more softly, or better, mute the microphone to ensure nothing gets through to the audience.
This is a very easy to understand video that I will be recommending to people.
This answer is spot on. Traditional digital cash schemes solved the double spending problem by having a centralized (online) entity that could check for coins being spent repeatedly. Bitcoin provides a nifty solution that works without a centralized entity by leveraging the proof of work. As long as honest nodes control the majority of the collective computing power, it's an uphill battle for a dishonest node to successfully double spend. Instead, they are better off mining themselves.
10 years later dawg. Tell me you hodl and are a absolute whale now
.
Volume is crazy low. Maybe increase it a bit?
Best video on the topic so far
Ótimo! Obrigado ao tradutor que traduziu este vídeo para português!
The intent was more to provide a detailed explanation of the mechanics of bitcoin since it's a question on many peoples' minds. Whether it's safe to put your money in bitcoins is an entirely different question. There are definitely many risks in doing so!
5:20 No need to reiterate portions of what you were building up to say. That confuses a typical person trying to understand every detail. In fact, the video editor should have cut that out, or replaced it -- with you restating a more clear message.
I love this bitcoin series. Very helpful.
did you buy bitcoin 7 years ago?
Yep. But there was a good article on read on this. Lets say an avalon miner runs at 60ghs and costs $1,500. BTC guild which do half of all mining is currently pooled at 35,757 ghs. So assume total is 2x this. So cost of creating a competing node would be $1,500x1000 or lets round up to $2m. Current value of BTC is ~$100m. $2m gamble, but do able.
God you for this priceless education - without these videos this member of the general public would be completely lost - you should seriously consider putting all of this information into a book format -
Easiest video to understand in CZcams for proof of work!
Finally, I could understand it. Thanks a lot! Your video was so useful!
Nice...but there are some other explanations needed e.g. who would be creating a challenge for miners to solve the puzzle and then who would be validating the outcome.
i don't know who creates the challenge but i would assume it would just be the blockchain itself considering that it is completely decentralized. the outcome of it is validated by many other nodes (miners) in the network mining at the time. so to put it simply a miner says they solved it and tells the other miners what they did to solve it, the many other miners all do it themselves to make sure it's correct (proof of work). once it is found and verified successfully by other miners in the network it is added to the blockchain
how does the "sever" know for certain that there even is a solution for its challenge?
Layman's guess here. There are, effectively, an infinite number of combinations of c and p' (you can literally make p' anything you want). There is a finite number of results to a cryptographic hash function (in the case of SHA256, that number is 2^256). If the proof of work is required to find p' such that the hash results in a number that has 30 leading zeros, then there are always 2^226 possible hashes that would satisfy the problem. I think.
In bitcoin, what is the challenge part and who validates it? What prevents a miner from just randomly generating a string with the correct number of zeros?
That cannot happen because the miner doesn't input the string with the number of zeros. Instead, he inputs a string that when hashed with the challenge string produces the number of zeros. The hashing that produces the string with zeros is done in the verification process, to which the miner has no access to.
Does the miner only need to include the nonce in the hash or is there any block information in the final proof of work hash?
This video would be a lot more valuable if you walked through an actual example, start to finish. You say 'for example', but then still work on a theoretical level (e.g. first 40 bits are 0). Show an example with actual data as to what it would look like on a website to how the calculations would be done, and how you would pick/create a challenge.
one suggestion, get your content on some page before starting the video, because when you take uncertain breaks in speaking, that disturbs the viewers link of understanding
Doesn't such a proof of work protocol open up the responder to application level DoS? For example I constantly send an intentionally wrong proof string to the responder, without trying to generate a valid one, to dismiss the proof as invalid the responder has to check the proof first by running it through the proof of work algorithm (such as sha256(sha256()) ), which should be significantly more computational power than to send the same packet over network @ 100mbit/s, am I on the right track?
I have a question. It'd be great if someone can explain.
It seems like this whole process depends on the hash function (both the proof of work, and validation). If an hash function is just an algorithm, or a mathematical formula, then one can work backwards as well as forwards.
What's stopping someone from finding out the hash algorithm and working backwards to find a valid hash code without working through the 1 trillion inputs?
You cannot, it works with the modulo which cannot be calculated backward. Thats what RSA is all about and why it is possible to authenticate yourself without someone creating Data in you name.
Hash functions are one way functions. Examples are MD5, SHA.
Fantastic videos. I send a link of your videos to people who want me to explain to them how cryptocurrency Et. al work.
I would like to mention however that the volume in these videos are extremely low which forces me to turn my speakers to 100% and I still have a hard time to hear what your saying.
Why to use n-number of leading zeros? Why exactly zeros?
might be good but can't hear correctly Sound too low by far
I didn't understand what problem it solves? apart from having a structured hash output? is it worth spending so much energy just to get the hash of desired pattern? Am I missing something here?
Just so that I understand, when you are trying to login to a site, to avoid multiple attempts, it is asking you to prove that you are human by selecting few images - do you call this "proof of work" - as it is work done by you to claim that you are actually human?
who decides what is the challenge ?
does it change from block to block? how?
thanks
ok
Why is this video so low? I can barely hear you.
Bitcoin provides a nifty solution that works without a centralized entity by leveraging the proof of work.
understood. thanks for the neat explanation
its really clear now. thanks!
You mean to tell me that's all we were talking about all day?
Thank you so much!
No. Its not like a physical coin. its just a number, or a value, of the amount of wealth you own, that is verified by the network.
Please tell me you bought Lucas
new coins come into existence when new blocks are created as a reward to the miner. Coins have to "mature" after a miner mints them and this takes a while. So its highly unlikely by that point that he will be in the possession of the longest blockchain which he could then use to attempt to double-spend. And so he could not double spend any more easily than anyone else for the same reasons why everyone else cant double spend.
Wow. That was amazing.
How did you manage to talk for so long about such a simple thing?
You spoke until your mouth got dry and all.
Very well done sir, very well done indeed.
While you could have just said "Some people want to verify that there is a person at the other end of the transaction. To do so they lay out a test. A test that an individual can solve with hard work much faster then a computer can. That test must then have a solution that is easy to check. Such as captcha." you didn't.
WAIT WHERE IS SAL?
Yo
I'm trying to understand how ButCoins work!! A "Miner" or a "Proof-of-Work" "node" appears to be nothing more than an accountant, A "node" being the person or volunteer mining (looking) for BitCoins. The BitCoin system relies of these "Nodes" - volunteer - to "Mine" for BitCoins by matheatically proving a "Transaction Block."
Cas someone tell me if I'm beginning to understand?
Are you millionaire now lol
The current value may be $100m but the market is not $100m deep at all. I can only guesstimate but would be surprised if you could sell over $500k in coins (fake or not) within a reasonable time.
lnternet RB lol
Cant hardly hear..
Couldn't you get lucky? I was expecting the proof of work to show that you didn't in fact just get lucky.
Obviously the odds of getting lucky are very small .. hence the 'luck'. Also I realize you mentioned luck at the 7 minute mark, but didn't say much about it.
Mining is the same as playing Numberwang.
ok?
hope that u invest in btc 8 years ago
*$1billion, not $100million
you are veryyyy quiet.....
Good point. $500k is a bit low imo.
sounds like commercial
AWESOME!!!!
Did you buy 8 years ago
from 2020
... and you didn't understand the concept :)
It seems like a massive waste of CPU and electric power.
You have to realize what it aims to achieve: to be a global alternative to the current banking system that has no trusted third parties (no middlemen). This is achieved through the proof of work. Think of all the global problems caused by corrupt elitists exerting control over others through banking and monetary policy. Even if bitcoin used 10 times more CPU/electrical power, it is absolutely worth it.
Some would say that energy companies are global elitists.
@@lincolnsghost7328 sure, but their ability to exert control over others seems rather limited when compared to the banking system. If I pay for electricity, they don't know what it's going towards (no way for them to know it is powering my small mining rig or whatever else). And the cost of running a small solar energy farm is becoming cheaper each year.
does it realy work inbox me ?
Yes
!
I don't get it! lol
lol true man jesus this guy
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the poo string!?!?! 💩
can you improve the audio, you're lowering Khan Academy standards. You should practice more. This is not up with Khan Academy quality.
OK. That was great! Now can you do: Bitcoin. Proof that is a scam?
How?
Your iq is too low for that video sorry pal