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

61–70 of 130 posts

Re: Proof-Of-Work is a Decentralized Clock

#61

Post by snissn »

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…

I think you'd want a Mars chain and an earth chain and have cross chain swaps for payments between planets

Re: Proof-Of-Work is a Decentralized Clock

#62

Post by danbruc »

gtrubetskoy wrote: post #57
danbruc wrote: post #52

Earlier quoted context omitted.

I just looked into the paper [1] for the first time but it says exactly what I wrote. Hashes in the blocks linking to previous blocks establish the ordering of transactions, proof of work limits the voting power of participants. The terminology could be somewhat more precise in distinguishing between the different components and their roles but it is still rather unambiguous about what does what. Chapter 3 - Timestam…

You are right that PoW does not establish order. The PoW "ticks" have a temporal order, but the way it is represented in the blockchain is cryptographically using a Merkle tree, and there is no "rule" that the real life appearance of "ticks" must match the blockchain order. Note that the paper says "_also_ solves", implying that the "representation in majority decision" part is secondary. If you think about it, the w…

I would argue the »also« is misplaced, that is really the only thing thing that the proof of work does. If you read the chapter, there is only an explanation how it works before the »also« but nothing else that is solved by the proof of work. And the miner does get to decide which transactions get included in the block, it creates the block, the block does not exist before.

Re: Proof-Of-Work is a Decentralized Clock

#63

Post by incompatible »

icebraining wrote: post #41
rocqua wrote: post #36

Earlier quoted context omitted.

Yeah, but it is quite interesting what the relevant target times are. Does a 10 minute delay require something like a 10 or 20 minute target time to keep consensus or is it more like 2 hours or even a day? How does is this effected by the ratio of hash-rates over the planets? What happens when you have clusters (say earth - moon and mars - phobos)? In any case, if the target times need to increase by too much, things…

Intuitively, for two planets, I'd say you need the delay to be inside (some percentile of) the variation between the time taken by each block, so that a planet has the chance to "leap ahead" of the other. So if a block takes X minutes with a 20% variation at, say, 95th percentile, and the inter-planet latency is 10 minutes, then I think the target time (X) must be more than 100 minutes, so that if Earth mined the las…

Earth would presumably still have the majority of the miners, so once they'd found a block they'd have a consensus. They'd ignore a block received from Mars that didn't build on that block. Mars wouldn't be able to do the same to Earth.

Re: Proof-Of-Work is a Decentralized Clock

#64

Post by gtrubetskoy »

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 is the input to the SHA).

PoW is a radically different approach - there is no leader, but there exist indisputable points in "blockchain time", and the order of blocks is determined by the longest chain, which is essentially a matter of chance.

Another related misconception is that PoW is good, but proof-of-stake is better. In fact, PoW is the evolution of PoS, not the other way around. A PoS based digital money was described 1998 by Wei Dai [1], but that approach had flaws that would only be overcome by a system described Nakomoto's Bitcoin paper.

1. http://www.weidai.com/bmoney.txt (B-Money, Wei Dai, 1998)

  "Each server is required to deposit a certain amount of
   money in a special account to be used as potential fines
   or rewards for proof of misconduct."

Re: Proof-Of-Work is a Decentralized Clock

#65

Post by hinkley »

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…

When Mars successfully mines a block in time the latency cancels out doesn’t it? Because now they know the next block ten minutes before everyone else.

Re: Proof-Of-Work is a Decentralized Clock

#66

Post by state_less »

danbruc wrote: post #58
state_less wrote: post #55

Earlier quoted context omitted.

Couldn't we save a lot of energy and have a distributed stores of identities (public keys) with ledgers, something like a git repo per identity? Whenever I want to spend money, I just commit a changelog to my repo, I want to transfer some credit to identity X, signed with my identity (private key). I sign the ledger with my private key and commit the entry to the distributed store. Push out the changes to anyone who…

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 a change that says, (pubkey:ae32...) paid (pubkey:af41...) 10 US dollars and reference my repo and commit.

I don't think there could be double spending because the receiver of the money acknowledges the credit offer on record (the git repo that paid).

If there are identities and entries in my ledger that are questionable, maybe you don't count them. For example, you might say credit only counts from those identities that are willing to answer a two-factor sms challenge. Or, if my git repo is credited by a google account, that's something worthwhile that could count toward my balance.

Re: Proof-Of-Work is a Decentralized Clock

#67

Post by IncRnd »

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 participant cannot steal the results created by another party.

Identification is generally accepted in the security community to come from something you are (biometrics), something you have (bank card), and something you know (pin for your bank card, password, etc). For safety, two separate classes are normally and simultaneously required for identification, hence the term two-factor id.

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.

Something You Can Do is not a new category of identification but a statement about processing power. This can be seen by simply sharing the private key of a wallet. In two factor identification, you could make a copy of someone's eye or face to try to get into a system, but two factor identification would stop you.

> And this is what proof of work does, it limits your ability to invent identities and cast as many votes as you would like by making casting a vote really hard respectively expensive.

Proof of work doesn't have anything to do with the ability to invent identities. It ties the result of processing power to keys. Digital keys are not identities any more than physical keys are houses. To construct a house, you need to perform the work. To get into a house, you need a key. To take possession of a key you need to identify yourself.

> a 51 % attack is just someone using a lot of money to buy more than half of all the available identities in the Bitcoin system granting him the majority of the available votes.

A 51% attack is when someone who may or may not use a lot of money forces an alternate version of a blockchain data structure by having 51% or more of the processing power. This has nothing to do with purchasing identities. You can test this for yourself. If you create two bitcoin wallets, you clearly didn't create two digital identities. You are the identity in possession of two keys for two separate wallets.

Besides, a 51% attack isn't 51% of the nodes but 51% of the processing power, which could be only 1 powerful node. Those are entirely different.

Re: Proof-Of-Work is a Decentralized Clock

#68

Post by gtrubetskoy »

danbruc wrote: post #62
gtrubetskoy wrote: post #57

Earlier quoted context omitted.

You are right that PoW does not establish order. The PoW "ticks" have a temporal order, but the way it is represented in the blockchain is cryptographically using a Merkle tree, and there is no "rule" that the real life appearance of "ticks" must match the blockchain order. Note that the paper says "_also_ solves", implying that the "representation in majority decision" part is secondary. If you think about it, the w…

I would argue the »also« is misplaced, that is really the only thing thing that the proof of work does. If you read the chapter, there is only an explanation how it works before the »also« but nothing else that is solved by the proof of work. And the miner does get to decide which transactions get included in the block, it creates the block, the block does not exist before.

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 never be. And if we could have Planck Time accuracy clocks, such a timestamp wouldn't come with a cryptographic proof like the PoW timestamp.

Everything else is secondary, an add on. The ordering is determined be the longest chain, recorded as a Merkle tree, transactions are tied by the strength of Elliptic Curve crytpography, miners motivated by rewards, etc.

But without that timestamp, none of it would work.

Re: Proof-Of-Work is a Decentralized Clock

#69

Post by Dylan16807 »

hinkley wrote: post #65
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…

When Mars successfully mines a block in time the latency cancels out doesn’t it? Because now they know the next block ten minutes before everyone else.

It's the total delay that matters. 10 minutes each way is functionally equivalent to 20 minutes earth-to-mars delay plus 0 minutes mars-to-earth delay. Or vice versa. There's no way to cancel out a single leg, because from the point of view of the computers it's impossible to know how long each leg is.

Re: Proof-Of-Work is a Decentralized Clock

#70

Post by danbruc »

gtrubetskoy wrote: post #68
danbruc wrote: post #62

Earlier quoted context omitted.

I would argue the »also« is misplaced, that is really the only thing thing that the proof of work does. If you read the chapter, there is only an explanation how it works before the »also« but nothing else that is solved by the proof of work. And the miner does get to decide which transactions get included in the block, it creates the block, the block does not exist before.

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 about the new block will arrive at different nodes at different times. End if you are really inclined to pull physics into this - which in my opinion hardly makes any sense - you have to face the fact that simultaneity is relative.

So you are really not tying the discovery of the new block to any specific point in time. Everything anybody can really say is that it happened before they received the block and after the block that is referenced by the previous block hash was mined which itself may have happened any time before they first received that block.

The previous block hash establishes a happened before relation between the events of creating the blocks in the chain and including a transaction in a block establishes a happened before relation between the creation of the transaction and the creation of the block. But nothing ties anything to any specific point in time. And proof of work plays no role here at all, you can simply calculate a single hash of a block and send it to me and that proofs that the block existed before I received that hash, no need to work hard to find a fancy hash with many leading zeros.

Post reply on HN