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Proof-Of-Work is a Decentralized Clock

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Re: Proof-Of-Work is a Decentralized Clock

#41

Post by icebraining »

rocqua wrote: post #36
icebraining wrote: post #34

Earlier quoted context omitted.

Now, I suppose if the hash-rate is more spread-out over multiple planets, and one planet isn't dominating things might work out. But we might also see consensus break down. I'm no expert, but wouldn't it just be a matter of increasing the target time to solve each block? An solar-system-wide blockchain might need to take a few hours rather than ten minutes between each block, but it should still work.

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 last block, Mars can receive it 10 minutes late and still have a chance of mining it first and reporting it back before Earth finds it.

But I'm probably totally wrong :)

Re: Proof-Of-Work is a Decentralized Clock

#43

Post by [deleted] »

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…

[deleted]

Re: Proof-Of-Work is a Decentralized Clock

#44

Post by rocqua »

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…

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 the 10 minute mark is at the moment. I imagine there might be nodes that are 5 seconds apart on the network. Maybe even more when we have backhoe outages. How much lower could the 10 minutes be before we start seeing to many orphans even on earth?

Re: Proof-Of-Work is a Decentralized Clock

#45

Post by rpearl »

drdrey wrote: post #21
xamuel wrote: post #2

Can someone who knows the technical details of bitcoin answer the following questions? Suppose initially A owns 1BTC and B owns 0BTC. Suppose A publishes a signed transaction that would give 1BTC to B, and simultaneously B publishes a signed transaction that would give 1BTC to C. If a miner includes both transactions in a block, is the block valid? Does it depend on the order of the transactions within the block (A's…

B would need to refer to a transaction output that has at least 1 BTC to be able to sign a transaction sending 1 BTC to B. Until A's transaction is included in a block, B can not do that.

> Until A's transaction is included in a block, B can not do that.

This is just not true at all?

for B to refer to A, it needs to know the transaction id.

Transaction ids are sha256(sha256(raw_transaction)) and a raw transaction consists of inputs and outputs. All this is known before the transaction gets put in a block--and has nothing to do with blocks.

Blocks and mining mitigate against double spending (...by burning an insanely huge amount of energy to do so, inefficiently. But that's a separate issue, at least right here)

Re: Proof-Of-Work is a Decentralized Clock

#46

Post by danbruc »

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 is totally unrelated to the proof of work.

I guess this has been said countless times before, but the role of proof of work is to establish a somewhat strange kind of identity among anonymous participants. If you had a trusted list of all participants, you could simply grant everyone one vote per block and decide by majority whether to accept or reject a block and get rid of the proof of work altogether. Of course using some cryptography to establish authenticity of votes and such.

But because Bitcoin is anonymous - or pseudonymous if you insist - there is no such list of participants and you need a mechanism to prevent participants from casting an arbitrary number of votes by essentially inventing identities. 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. The capital costs and the energy consumption of your warehouse full of ASIC miners become a proxy for your identity via their hashing power.

And that's it, nothing more, nothing less. The rest follows from here, for example 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.

Re: Proof-Of-Work is a Decentralized Clock

#47

Post by IncRnd »

> The Bitcoin blockchain Proof-of-Work is simply a distributed, decentralized clock.

While this is a cute way of looking at the issue it also isn't true. The bitcoin blockchain gets updated on average every 10 minutes with the data produced by proof of work.

The author is saying that the cart pulls the horse, because they are both moving.

Re: Proof-Of-Work is a Decentralized Clock

#48

Post by discussedbefore »

rocqua wrote: post #22
xamuel wrote: post #2

Can someone who knows the technical details of bitcoin answer the following questions? Suppose initially A owns 1BTC and B owns 0BTC. Suppose A publishes a signed transaction that would give 1BTC to B, and simultaneously B publishes a signed transaction that would give 1BTC to C. If a miner includes both transactions in a block, is the block valid? Does it depend on the order of the transactions within the block (A's…

Yes, and this actually has a use. You can use this to increase the fee of a transaction after the fact. So, suppose A has a fee of 0.001 in the first transaction, and the current fee needs to be 0.01 . Then, B has this transaction, but no-one will put it into a block, so B hasn't really received his money yet. A could sign another transaction with a higher fee that would send the money back to A. This could happen un…

> increase the fee of a transaction after the fact

Someone should have volunteered to help the Pineapple Fund do this instead of switching to Bitcoin Cash (or maybe this is what "Child-Pays-For-Parent" is, and it cost too much). https://news.ycombinator.com/item?id=15995391

>> Since this created a series of unconfirmed transactions, we had to do something drastic: use Child-Pays-For-Parent with a very significant fee.

Re: Proof-Of-Work is a Decentralized Clock

#49

Post by leereeves »

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…

A long enough interval could work within the solar system, but without FTL communication, an actual intergalactic version would require intervals longer than human lifespans.

It seems to me that different solar systems wouldn't be able to maintain a single blockchain, they'd each need their own.

Re: Proof-Of-Work is a Decentralized Clock

#50

Post by pdpi »

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…

> This analysis is obviously wrong, if the important thing was establishing a global clock, you could just use GPS receivers

Is it so obviously wrong? From the first paragraph of the introduction to Satoshi's Bitcoin Paper: "In this paper, we propose a solution to the double-spending problem using a peer-to-peer distributed timestamp server to generate computational proof of the chronological order of transactions".

GPS is a trusted system, whereas bitcoin is designed to be completely trust-less. The reason why timestamping is a difficult problem is that if I publish two transactions spending the same money, the network must agree on the order of events (which is to say: must assign different timestamps to the two transactions) so that one is considered valid, and the other invalid. Doing this without proof-of-work leaves you vulnerable to Sybil attacks, where I can pretend to have an overwhelming amount of nodes in the consensus, and vote for the more favourable (to me) transaction to be considered the canonical one.

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