Financial Cryptography

Proof of Work made useful -- auctioning off the calculation capacity is just another smart contract

Just got tipped to Andrew Poelstra's faq on ASICs, where he says of Adam Back's Proof of Work system in Bitcoin:

In places where the waste heat is directly useful, the cost of mining is merely the difference between electric heat production and ordinary heat production (here in BC, this would be natural gas). Then electricity is effectively cheap even if not actually cheap.

Which is an interesting remark. If true -- assume we're in Iceland where there is a need for lots of heat -- then Bitcoin mining can be free at the margin. Capital costs remain, but we shouldn't look a gift horse in the mouth?

My view remains, and was from the beginning of BTC when Satoshi proposed his design, that mining is a dead-weight loss to the economy because it turns good electricity into bad waste, heat. And, the capital race adds to that, in that SHA2 mining gear is solely useful for ... Bitcoin mining. Such a design cannot survive in the long run, which is a reflection of Gresham's law, sometimes expressed as the simplistic aphorism of "bad money drives out good."

Now, the good thing about predicting collapse in the long run is that we are never proven wrong, we just have to wait another day ... but as Ben Laurie pointed out somewhere or other, the current incentives encourage the blockchain mining to consume the planet, and that's not another day we want to wait for.

Not a good thing. But if we switch production to some more socially aligned pattern /such as heating/, then likely we could at least shift some of the mining to a cost-neutrality.

Why can't we go further? Why can't we make the information calculated socially useful, and benefit twice? E.g., we can search for SETI, fold some DNA, crack some RSA keys. Andrew has commented on that too, so this is no new idea:

7. What about "useful" proofs-of-work?

These are typically bad ideas for all the same reasons that Primecoin is, and also bad for a new reason: from the network's perspective, the purpose of mining is to secure the currency, but from the miner's perspective, the purpose of mining is to gain the block reward. These two motivations complement each other, since a block reward is worth more in a secure currency than in a sham one, so the miner is incentivized to secure the network rather than attacking it.

However, if the miner is motivated not by the block reward, but by some social or scientific purpose related to the proof-of-work evaluation, then these incentives are no longer aligned (and may in fact be opposed, if the miner wants to discourage others from encroaching on his work), weakening the security of the network.

I buy the general gist of the alignments of incentives, but I'm not sure that we've necessarily unaligned things just by specifying some other purpose than calculating a SHA2 to get an answer close to what we already know.

Let's postulate a program that calculates some desirable property. Because that property is of individual benefit only, then some individual can pay for it. Then, the missing link would be to create a program that takes in a certain amount of money, and distributes that to nodes that run it according to some fair algorithm.

What's a program that takes in and holds money, gets calculated by many nodes, and distributes it according to an algorithm? It's Nick Szabo's smart contract distributed over the blockchain. We already know how to do that, in principle, and in practice there are many efforts out there to improve the art. Especially, see Ethereum.

So let's assume a smart contract. Then, the question arises how to get your smart contract accepted as the block calculation for 17:20 on this coming Friday evening? That's a consensus problem. Again, we already know how to do consensus problems. But let's postulate one method: hold a donation auction and simply order these things according to the amount donated. Close the block a day in advance and leave that entire day to work out which is the consensus pick on what happens at 17:20.

Didn't get a hit? If your smart contract doesn't participate, then at 17:30 it expires and sends back the money. Try again, put in more money? Or we can imagine a variation where it has a climbing ramp of value. It starts at 10,000 at 17:20 and then adds 100 for each of the next 100 blocks then expires. This then allows an auction crossing, which can be efficient.

An interesting attack here might be that I could code up a smartcontract-block-PoW that has a backdoor, similar to the infamous DUAL_EC random number generator from NIST. But, even if I succeed in coding it up without my obfuscated clause being spotted, the best I can do is pay for it to reach the top of the rankings, then win my own payment back as it runs at 17:20.

With such an attack, I get my cake calculated and I get to eat it too. As far as incentives go to the miner, I'd be better off going to the pub. The result is still at least as good as Andrew's comment, "from the network's perspective, the purpose of mining is to secure the currency."

What about the 'difficulty' factor? Well, this is easy enough to specify, it can be part of the program. The Ethereum people are working on the basis of setting enough 'gas' to pay for the program, so the notion of 'difficulty' is already on the table.

I'm sure there is something I haven't thought of as yet. But it does seem that there is more of a benefit to wring from the mining idea. We have electricity, we have capital, and we have information. Each of those is a potential for a bounty, so as to claw some sense of value back instead of just heating the planet to keep a bunch of libertarians with coins in their pockets. Comments?

Posted by iang at September 3, 2014 02:12 PM | TrackBack