Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Proof-Of-Work is a Decentralized Clock

grisha.org

Post reply on HN
Print view View original

71–80 of 130 posts

Re: Proof-Of-Work is a Decentralized Clock

#71

Post by gtrubetskoy »

rocqua wrote: post #44
gtrubetskoy wrote: post #39

Earlier quoted context omitted.

>> Mostly the claim that "The Difficulty is Intergalactic" is just flat wrong. (I wrote the article) - I see your point, but I think the article is still correct. Now communicating the winning block is a problem, as you pointed out, so as a miner on Mars you're at a disadvantage, but that statistically the probability of solving the puzzle remains same regardless of your location in the universe is still true. As som…

Hi, I hope my tone wasn't too grating. I stand by my point though, for the purpose of totally ordering blocks, the difficulty is not intergalactic because a solution on mars is much less useful than a solution on earth. The problem here is time-delay preventing simultaneity. This is the same problem that block chain time-stamping hopes to solve. Thus it seems unfair to me to ignore this problem. I wonder how tight th…

> the difficulty is not intergalactic because a solution on mars is much less useful than a solution on earth

We're talking apples and oranges, I don't think there is a disagreement - I was only saying that the statistical problem is "intergalactic", not that how it's used in Bitcoin is useful across galaxies. The fact that the probability of the outcome is same across the whole universe is what I found particularly remarkable.

Re: Proof-Of-Work is a Decentralized Clock

#72

Post by gtrubetskoy »

rocqua wrote: post #30

I think some of this is kind of wrong. Mostly the claim that "The Difficulty is Intergalactic" is just flat wrong. Consider a miner on mars with 10% of the hash-rate on earth. Lets say the light delay from earth to mars is 10 minutes (it is 14 on average). Now, suppose mars has last seen block B_0 and it was mined on earth (as would happen most often due to 90% of the hash rate being there). We will call E_1 the next…

>> SHA is Memoryless and Progress-Free

> Technically false, because memory-less processes have positive probabilty of yielding no block after 2^256 tries, whereas for sha-256 using brute force, this probability is totally 0. I don't think this matters at the current hash-rate though.

You may be right about my use of "memoryless", though it won't matter at any hashrate :) "...brute-force attacks against 256-bit keys will be infeasible until computers are built from something other than matter and occupy something other than space" (B. Schneier "Applied Cryptography").

Re: Proof-Of-Work is a Decentralized Clock

#73

Post by mad44 »

gtrubetskoy wrote: post #64
mad44 wrote: post #42

https://muratbuffalo.blogspot.com/2018/03/anatomical-similar... Proof of work is the leader election phase of consensus. It is followed by the accept phase, where the leader broadcasts the decision to be accepted. The commit comes eventually and as probabilistic.

> Proof of work is the leader election phase of consensus. This is a common misconception stemming from looking at PoW through the Paxos/RAFT prism. In Paxos a leader is elected, then the leader decides the order of events. But that's not a valid comparison, because in PoW the supposed "leader" does not get to decide anything at all - the block has to be put together prior to "winning the election" (because the block…

Leaders don't decide. They propose values (such as a block of transactions). There may be multiple leaders with different proposals and participants get to a consensus about which proposal gets accepted for a given slot.

You speak authoritatively, saying "this is a common misconception", but blockchain is a distributed consensus protocol and I don't think you are familiar with multileader and leaderless flavors of distributed consensus.

Re: Proof-Of-Work is a Decentralized Clock

#74

Post by danbruc »

IncRnd wrote: post #67
danbruc wrote: post #46

This analysis is obviously wrong, if the important thing was establishing a global clock, you could just use GPS receivers. Ordering transactions works also without proof of work, just including a hash of an existing transaction or block in a new transaction or block and this proofs the order of those transactions or blocks relative to each other. No clock required at all. And also exactly what Bitcoin does but which…

Your post is very dangerous from a security perspective and may misinform many people who are still learning about digital identification. > the role of proof of work is to establish a somewhat strange kind of identity among anonymous participants. The role of proof of work is to make the creation of information one-way based upon a pre-specified amount of work. Therefore, in a properly constructed system, a particip…

The role of proof of work is to make the creation of information one-way based upon a pre-specified amount of work. Therefore, in a properly constructed system, a participant cannot steal the results created by another party.

That makes no sense, or the meaning is at least not obvious. What does it mean to make creation of information one-way? Proof of work is just a vote allocation scheme. We want to reach consensus about what the transaction history is and do so by a majority vote and therefore we have to decide who gets how many votes.

This alone has no single obviously correct solution, for example, if I have a company with a company account, do I get one vote for the company or do I get a thousand votes because the company has a thousand employees? Or maybe votes proportional to the amount of money in the account? And if the system is anonymous it gets even harder because there is no easy way to know who cast a vote or if someone cast a million votes.

And that is the way in which I used identity, the identity of an entity allowed to cast a specific amount of votes. And that is what proof of work does, a collection of mining hardware establishes an entity with a voting power proportional to its hashing power.

Identification is generally accepted in the security community to come from something you are (biometrics), something you have (bank card), and [...] An identity is something entirely different from work. Proof of work, since it is one-way, proves that work was performed. This has nothing to do with identity, which cannot be proved by work.

As explained above, I was not using identity in the computer security sense but in the sense of the identity of entities with a certain amount of voting power. And all your other remarks essentially also hinge on a misunderstanding of my use of identity, if you read it as entities with voting power it will certainly make more sense.

Re: Proof-Of-Work is a Decentralized Clock

#75

Post by gtrubetskoy »

danbruc wrote: post #70
gtrubetskoy wrote: post #68

Earlier quoted context omitted.

Think of it this way: the block is the input to SHA. When the puzzle is solved, that block happens exactly at the time the puzzle is solved, and no one cannot dispute it. There is no other way (or at least none that I can think of) to link a pile of data to a point in time. The only way you'd get this level of accuracy with a traditional clock is if you could measure/record Planck Time, which isn't possible and might…

Nope. You find a good hash at a specific point in time, but that is nothing special, every event happens by its very definition at a specific point in time. Committing a database transaction, potentially including finical transaction records, occurs at a specific point in time. But that is all without consequences, nobody will know about this event until you broadcast and they receive your block. And the message abou…

The valid sha ties this block to the exact point in time at which the solution was found. We can't know exactly what time in hh:mm:ss that was, but we do know the chain height, and the height is how "blockchain time" is told.

The fact that the block time (i.e. height) is when the conforming SHA was found is indisputable. Also that no other block happened at this same point in time.

Re: Proof-Of-Work is a Decentralized Clock

#76

Post by PKop »

state_less wrote: post #66
danbruc wrote: post #58

Earlier quoted context omitted.

The problem is, where do your coins come from? Who or what is allowed to bring coins into existence and what prevents them from just creating as many as they like? The second problem is, how do you resolve conflicting transactions spending the same coins?

There wouldn't be any coins, instead double entry accounting I (pubkey:ae32...) owe (pubkey:af41...) 10 US dollars. Medium of exchange is agreed upon by the two parties, USD is one option. If you're my friend or a business, and you see my balance is deeply negative, maybe you don't give some service. If your my friend or a business, and my credit is not too bad, you follow my repo and give me some service. You commit…

"There wouldn't be any coins"

"USD is one option"

And now you have no restriction on the money supply.. USD is coins.

Re: Proof-Of-Work is a Decentralized Clock

#77

Post by dlubarov »

IncRnd wrote: post #67
danbruc wrote: post #46

This analysis is obviously wrong, if the important thing was establishing a global clock, you could just use GPS receivers. Ordering transactions works also without proof of work, just including a hash of an existing transaction or block in a new transaction or block and this proofs the order of those transactions or blocks relative to each other. No clock required at all. And also exactly what Bitcoin does but which…

Your post is very dangerous from a security perspective and may misinform many people who are still learning about digital identification. > the role of proof of work is to establish a somewhat strange kind of identity among anonymous participants. The role of proof of work is to make the creation of information one-way based upon a pre-specified amount of work. Therefore, in a properly constructed system, a particip…

It seems like your criticizing his analogous use of "identity", but not the underlying idea.

Perhaps the idea is more clear if it's framed in terms of votes rather than identities. Mining on top of a particular fork can be viewed as voting for that fork. Each participant's number of votes is proportional to their hash power. Double voting is impossible since the same hardware can't mine on more than one fork without splitting its hash power.

Re: Proof-Of-Work is a Decentralized Clock

#78

Post by danbruc »

state_less wrote: post #66
danbruc wrote: post #58

Earlier quoted context omitted.

The problem is, where do your coins come from? Who or what is allowed to bring coins into existence and what prevents them from just creating as many as they like? The second problem is, how do you resolve conflicting transactions spending the same coins?

There wouldn't be any coins, instead double entry accounting I (pubkey:ae32...) owe (pubkey:af41...) 10 US dollars. Medium of exchange is agreed upon by the two parties, USD is one option. If you're my friend or a business, and you see my balance is deeply negative, maybe you don't give some service. If your my friend or a business, and my credit is not too bad, you follow my repo and give me some service. You commit…

So the entire thing starts with everyone having a balance of zero. Then A signs a transaction that he gives $1000 to B and we broadcast that transaction, new balances A $-1000, B $+1000. Now B wants to buy something for $500 from C and signs a matching transaction. What does C do? Is A a bank that provided a $1000 loan and therefore C will be able to actually get $500 from A? Or are A and B one and the same poor guy who just created two keys and invented $1000 out of thin air?

Maybe I am missing something but I have no idea how that could ever work unless this is essentially just the current banking system were I know that A is a trustworthy bank and I will be able to redeem your $500 check. Augmented with the anti-feature that we are now all broadcasting our balances and all our transactions to everyone.

Re: Proof-Of-Work is a Decentralized Clock

#79

Post by skybrian »

gtrubetskoy wrote: post #39
rocqua wrote: post #30

I think some of this is kind of wrong. Mostly the claim that "The Difficulty is Intergalactic" is just flat wrong. Consider a miner on mars with 10% of the hash-rate on earth. Lets say the light delay from earth to mars is 10 minutes (it is 14 on average). Now, suppose mars has last seen block B_0 and it was mined on earth (as would happen most often due to 90% of the hash rate being there). We will call E_1 the next…

>> Mostly the claim that "The Difficulty is Intergalactic" is just flat wrong. (I wrote the article) - I see your point, but I think the article is still correct. Now communicating the winning block is a problem, as you pointed out, so as a miner on Mars you're at a disadvantage, but that statistically the probability of solving the puzzle remains same regardless of your location in the universe is still true. As som…

While you don't have to report that you failed to calculate a hash, it matters that, had you succeeded, you would have reported it. Someone who calculates hashes with no ability to report them shouldn't count as a participant.

To put it another way: if there is a group of participants with spotty Internet that, after succeeding in calculating a hash, have only 10% chance of actually reporting it, then working backwards, we need to divide by .1 (multiply by 10) to calculate the number of participants. But if they have a 0% chance of reporting success, then we'd have to divide by zero. This is because they aren't actually participants. It's attempting to count non-participants.

Re: Proof-Of-Work is a Decentralized Clock

#80

Post by danbruc »

gtrubetskoy wrote: post #75
danbruc wrote: post #70

Earlier quoted context omitted.

Nope. You find a good hash at a specific point in time, but that is nothing special, every event happens by its very definition at a specific point in time. Committing a database transaction, potentially including finical transaction records, occurs at a specific point in time. But that is all without consequences, nobody will know about this event until you broadcast and they receive your block. And the message abou…

The valid sha ties this block to the exact point in time at which the solution was found. We can't know exactly what time in hh:mm:ss that was, but we do know the chain height, and the height is how "blockchain time" is told. The fact that the block time (i.e. height) is when the conforming SHA was found is indisputable. Also that no other block happened at this same point in time.

The valid sha ties this block to the exact point in time at which the solution was found.

It does not, it just sets a lower bound on the time. I can totally mine a block linking directly to the genesis block today. All it proofs is that it happened after the previous block was created. And so does SHA() without any mining.

Also that no other block happened at this same point in time.

Also not true, I can totally mine several blocks all linking back to the same block. And with some luck that might also happen at the exact same point in time.

Post reply on HN