Topic: Funding of network security with infinite block sizes - page 2. (Read 24563 times)

Actually you just need OP_TRUE as the scriptPubKey, or leave it empty and have the miner provide OP_TRUE in the scriptSig. I mentioned the trade-offs of the approach on IRC a few weeks ago.


Ouch... not much of an assurance contract then is it? It's basically just a donation at random - that's very clever of you. There is of course the risk that your block gets orphaned and another miner takes the fees instead, but that happens something like 1% of the time now, and potentially a lot less in the future. Miners can deliberately orphan the block too, but we really want to implement mechanisms to discourage that behavior for a lot of reasons.

You could use nLockTime: basically you would all participate in authoring an nLockTime'd assurance contract transaction. Some time before the nLockTime deadline approaches, if the assurance contract is *not* fully funded, IE a miner might pull the "self-assure" trick, you double-spend the input that would have gone to the contract so your contribution to it is no longer valid. On the other hand, that means anyone can DoS attack the assurance contract process itself by doing exactly that, and if they time it right, they can still pull off the "self-assure" trick. Risky though - it's hard to reason about what is the correct strategy there, although it's obviously easier to pull off all those attacks if you control a large amount rather than a small amount of the overall hashing power.

With a hardfork we can fix the issue though, by making it possible to write a scriptPubKey that can only be spent by a transaction following a certain template. For instance it could say that prior to block n, the template can only be a mining fee donation of value > x, and after, the spending transaction can be anything at all. It'll be a long time before that feature is implemented though.

In any case all these tricks would benefit an attacker trying to depress the overall network hash rate, either to launch double-spend attacks, attack Bitcoin in general, or just keep funds from flowing to the competition if they are a miner.

When you propagate them, do you send them to all other miners or only a subset of miners?

So, the procedure is basically, create a transaction:

Inputs:
2: + SIGHASH_ANYONECANPAY

Outputs
10: OP_RETURN

This transaction cannot be spent.  However, when performing the authentication, all other inputs are ignored.  This means that if someone modified it to

Inputs:
2: + SIGHASH_ANYONECANPAY
8: + SIGHASH_ANYONECANPAY

Outputs
10: OP_RETURN

It becomes valid.  The tx is validated twice, once with each input and the keys have to all be valid.

It seems that you can get the same effect without OP_RETURN by having a transaction that pays to OP_TRUE OP_VERIFY.

Also, what is to stop a miner adding the extra 8 BTC to get it over the limit?  In that case, the block is funded anyway.

The disadvantage is that the miner must add a 2nd transaction to direct the OP_TRUE output to his actual address.  However, no hard fork is required.

No, a block takes the same time to solve, no matter how many transactions are in it.  You only have to solve the block header which is 80 bytes.  You run the header through the sha-256 hash function twice to see if you "win".  If not, you increment an integer in the header and try again.  Mining is repeating the hash function until you get an integer than "wins".

Basically, once you have generated all the transactions you want to add, you calculate the merkle root.  This is a hash for all the transactions.  You include that number in the header and it is always the same size (32 bytes).

Larger blocks will potentially cause bandwidth issues when you try to propagate them though, since you have to send all the transactions.

Can someone explain why limited blocksizes limit the number of transactions that can be placed? Wouldnt 10 100kb blocks get solved in as much time as 1mb block?

Coolness - keep up the good work Mike!

The wiki page is basically a copy of what I wrote with a few edits to make it sound more wiki-ish.

Posted the wiki article to reddit.

I haven't read the thread in a while. Can I assume the wiki is relatively up to date, or does it need updating?

Nah, I now think that's a dumb idea.

Responding to gmaxwell:

RE: burden of unpaid full nodes: for the immediately forseeable future, that burden is on the order of several hundred dollars a year to buy a moderately beefy VPS somewhere.

I understand the "lets engineer for the far future" ... but, frankly, I think too much of that is dumb. Successful projects and products engineer for the next year or two, and re-engineer when they run into issues.

Maybe the answer will be "validation pools" like we have mining pools today, where people cooperate to validate part of the chain (bloom filters, DHTs, mumble mumble....). Maybe hardware will just keep up.

RE: race to the bottom on fees and PoW:

sigh.  Mike explained how that is likely to be avoided. I'm 100% convinced that if users of the network want secure transactions they will find a way to pay for them, whether that is assurance contracts or becoming miners themselves.

it also guarantess that bitcoin always costs more than 8,7%-16,2% of its current market cap in fees. sounds like a solid plan. at 100 billion dollar market cap we need to start thinking about invading some small countries for mining rig storage space though.

What about directly targeting fees, similar to Gavin's suggestion that blocks must have fee > 50 * (size in MB).

If the average (or median) block fee (including minting) for the last 2016 blocks is more than 65, then increase the block size by 5%.  If it is less than 35, then drop it by 5%.  This gives a potential increase in block size of 3.5 per year approx.  It also guarantees that the miner fees stay between 35 and 65 per block, so keeps the network secure.

Ofc, if decreased block size causes decreased usage, which causes less tx fees, then you could get a downward spiral, but the limit is a factor of 3.5 per year in either direction.

Meh.

Any amount of algorithms will just be guesswork that could be wildly wrong— A small error in the exponent makes a big difference: If computer's ability to handle the blocks doubles in 18 months instead of 12 then ten years the size increase will be 1024 : 101— blocks 10x too big to handle.

And "median of blocks" basically amounts to "miner's choose"— if you're going to have miners choose, I'd rather have them insert a value in the coinbase and take the median of that... then at least they're not incentivized to bloat blocks just to up the cap, or forced to forgo fees to their competition just to speak their mind on making it lower.  But miners choose is ... not great because miners alignment with everyone else is imperfect— and right now the majority of the mining decision is basically controlled by just two people.

There are two major areas of concern from my perspective:  The burden on unpaid full nodes making Bitcoin not practically decentralized if it grows faster than technology, and a race to the bottom on fees and thus PoW difficulty making Bitcoin insecure (or dependent on centralized measures like bank-signed-blocks).  (and then there are then some secondary ones, like big pools using large blocks to force small miners out of business)

If all of the cost of being a miner is in the handling of terabyte blocks and none in the POW, an attacker who can just ignore the block validation can easily reorg the chain. We need robust fees— not just to cover the non-adaptive "true" costs of blocks, but to also cover the POW security which can adapt as low as miners allow it.

The criteria you have only speak to the first of these indirectly— we HOPE computing will follow some exponential curve— but we don't know the exponent.  It doesn't speak to the second at all unless you assume some pretty ugly mining cartel behavior to fix the fee by a majority orphaning valid blocks by a minority (which, even if not too ugly for you on its face would make people have to wait many blocks to be sure the consensus was settled).

If you were to use machine criteria, I'd add a third: It shouldn't grow faster than (some factor of) the difficulty change.  This directly measures the combination of computing efficiency and miner profitability.  Right now difficulty change looks silly, but once we're comfortably settled w/ asics on the latest silicon process it should actually reflect changes in computing... and should at least prevent the worst of the difficulty tends to 1 problem. (though it might not keep up with computing advances and we could still lose security).  Also, difficult as a limit means that miners actually have to _spend_ something to increase it— the median of size thing means that miners have to spend something (lost fees) to _decrease it_...  

Since one of my concerns is that miners might not make enough fees income and the security will drop, making it so miners have to give up more income to 'vote' for the size to go down... is very not good. Making it so that they have to burn more computing cycles to make it go up would, on the other hand, be good.

(the 100m number there is completely random, we'll have to see what things look like 8 months once the recent difficulty surge settles some, otherwise I could propose something more complicated than a constant there.)

Mind you— I don't think this is good by itself. But the difficulty based check improves it a lot. If you were to _then_ augment these three rules with a ConsentOfTheGoverned hard upper limit that could be reset periodically if people thought the rules were doing the right thing for the system and decentralization was being upheld...  well, I'd run out of things to complain about, I think. Having those other limits might make agreeing on a particular hard limit easier— e.g. I might be more comfortable with a higher one knowing that there are those other limits keeping it in check. And a upper boundary gives you something to test software against.

I'm generally more of a fan rule by consent— public decisions suck and they're painful, but they actually measure what we need to measure and not some dumb proxies that might create bad outcomes or weird motivations— there is some value which is uncontroversial, and it should go to that level. Above that might be technically okay but controversial, and it shouldn't go there.   If you say that a public set limit can't work— then you're basically saying you want the machine to set behavior against the will and without consent of the users of the system, and I don't think thats right.
 

+1

Okay, I think this will be my final word on this (if anyone cares or is listening).

Basically it comes down to a philosophical call since the number of variables and unknowns going into the decision lead to an incalculable analysis, at least I don't see any good way to reduce the variable set to get a meaningful result without over-simplifying the problem with speculative, weak assumptions.

In that case, as Gavin is saying, we should just leave it up to the market, our intuitions, our future ingenuity, trust in ability to solve anything that comes up and basically hope for the best.

So now I'm thinking, let the max_block_size float up to any unlimited size. But have a limit on how fast it can rise that makes practical sense, a rate limiter of some sort so it can grow as fast the network grows but not so fast that an attacker could game it over the medium/short term to force smaller users off the network with unrealistic hardware upgrade requirements. Ultimately though have an infinite limit to max block size in the long term, as Mike Hearn says.

As a first blush in pseudo-code;


Infinite max block size growth possible but rate limited to yearly doubling rate.

You are assuming things are problems with no evidence.  It's quite easy to ignore troublemakers, e.g. the anti-spam rules.  Think outside the box a bit more.  Central planners almost never get anything right, stop wanting others to solve your problems.

Despite all the claims of trouble-making large blocks, the only one we really had over 500k was recently, and the only reason that caused a problem was entirely unrelated, owing to limitations of untested parts of the software, untested so late only because of all these special case rules.  Let miners be free and figure it out for themselves.  I suspect a common core of rule(s) would be generally agreed (anti-spam etc.) and others would all do their own thing on the fringes, which is actually the case now.

People tend not to want to murder others or be murdered themselves, yet it still happens and we have laws to prevent / discourage it.


You're working under the assumptions that everyone mining coins want what's best for Bitcoin / care about Bitcoin's future, and all miners are equal - they are not, some will realize that producing large blocks that others can't handle is very much in their interest. Others may have the aim of just causing as many problems as possible because Bitcoin is a threat to them in some way, who knows? All you're doing is creating a vulnerability and expecting no-one to take advantage.

We aren't all hippies living on a fucking rainbow - problems don't just fix themselves because in your one-dimensional view of the world you can't imagine anyone not acting rationally and for the greater good.

Gathering data does not imply blindly following the data's source.

Fully understanding the intent of the system's designer WRT fees is a very valuable data point in making a decision on block size limits.

Add my vote too.  Other stances have the premise that block space is valuable and can't be allowed to get too big too fast, but with the contradictory fear that it would be given away for free. And that miners would allow such large blocks to be created that miners wouldn't be able to handle it, which is also a self-correcting "problem".

Block space will always come with a price, it has for 2 years now despite 1MB not being a limiting number. Miners worry about their block propagation and always will have the incentive to be conservative and get their blocks known. See Eligius for example with 32 transactions limit for a long time.

Let the miners determine what works in the free market through trial and error.  This will change with time elastically as computing power and resources change. And that's the way it should be.

I know people are tired of the 20+ threads on block size and thousands of posts in them, but this exhaustive debate is very good.

The minutiae of every point of view is being thrashed out in the open, smart ideas and not so smart ideas are put forward and critiqued. What is the alternative? Important decisions taken behind closed doors. Isn't that the default model of existing CBs?

I think that this debate has been productive because a lot of information has been shared between people who care about Bitcoin and want to contribute to help it become successful.

I support it too. Letting the market decide the fees and the maximum blocksize is the right answer.

I happen to believe that a limited blocksize will lead to centralization, but for those that think the opposite (that larger blocksizes lead to centralization), I truly wish they would put their time and effort into helping BITCOIN scale. If you are concerned about computing requirements going up for the average user, you can certainly work towards optimizations that will lighten that load, without trying to replace Bitcoin for the majority of what constitutes its present day usage. I think thats probably why Gavin is working on the payment protocol, so that dead puppy "communication" isn't needed.  

All the effort and time spent discussing this issue... imagine if it was actually used productively.