3 ms·

Do that and it would no longer be useful as proof of work. Proof of work-i-was-going-to-do-anyway is not useful for securing the ledger.

by kobeya 9y ago

akvadrako 9y ago
That's incorrect. All that matters is you can't game the system by taking shortcuts or deciding what the problem will be beforehand; the work cannot be even partially computable without knowing the previous block.
- spiorf 9y ago
  But there is no known function that has these properties and is useful in real world.
  - akvadrako 9y ago
    Sure and that puts it in the same camp as PoS and other currently unworkable schemes. A possible way forward; we don't know yet.
- Taek 9y ago
  No, you are incorrect. The important aspect of proof of work is that it is very expensive to create an alternate history (maybe one where you didn't send $15,000,000 to the exchange, for example). If you are doing useful work, someone can pay for it, and you can use that payment to make an alternate history for free, defeating the security assumption of blockchains. Blockchains only work by probably wasting in order to build a history. If you aren't wasting, then it wasn't expensive to build the history (it was subsidised), and it wouldn't be expensive to build a different history (that one could also be subsidized)
  - SilasX 9y ago
    But "socially useful" does not imply saleable (to the bane of venture capitalists everywhere). It's possible for something to provide a social benefit but not make sense for anyone to pay for as a for-profit business because others would get the same benefit and free ride off them. (Hence the problem of public goods in economics.) So if the proof of work is only solving some general research problem, then it might not be feasible to double dip like you've described. That's why primecoin was able to avoid the problem.
    - Taek 9y ago
      Primecoin also ultimately had limited utility. It found the world's largest prime number thousands of times, continually beating it's own record. At some point we had more prime numbers than had mathematical utility. My unprovable guess is that any other non-sellable problem will ultimately have the same outcome. It's interesting and useful for a bit, but when you have a billion dollars of hardware grinding nonstop for years in a row, you eventually exhaust everything interesting about the original problem and then it's back to the same waste you started with.
      - SilasX 9y ago
        Doesn't that mean it worked too well, and we just need to make a Coin with harder and more useful problems?
    - kobeya 9y ago
      There are very few things that are actually useful (socially or otherwise) but don't provide economic incentive. As pointed out by others primecoin isn't really a very good example. A good application to shoot for, if there are any budding cryptographers in the audience, is a ticking timelock encryption. A set of keys known in advance, and each block solves the next key. This would let you encrypt messages into the future, where the cost to decrypt is equal to the cost of minting that many blocks. I've seen partial schemes for this, but no complete ones that would justify implementation. If a full and workable scheme could be devised, I would bet on it replacing sha256 based proof of work, eventually.
      - SilasX 9y ago
        Every public goods problem is mathematical research is a case where the solutions are socially useful but not saleable. The problem (pointed out by the sibling) with primecoin was that it worked too well, such that further solutions were uninteresting and past the point of diminishing returns. Edit: See my here for a model of how NP complete problems could fill the role of you could predict difficulty in advance. There wouldn't be double dipping because the person wanting the answer wouldn't pay both bounties. https://news.ycombinator.com/item?id=15107653 https://news.ycombinator.com/item?id=15107653
  - akvadrako 9y ago
    It doesn't matter if the work is profitable because you only need to create an alternate history for a few blocks. If you attack the network you can steal billions - so if you have that much computing power available for your useful work, you can temporarially use it against the block chain. As long as that mining power is available anywhere the chain isn't secure.

Do that and it would no longer be useful as proof of work. Proof of work-i-was-going-to-do-anyway is not useful for securing the ledger.

by kobeya 9y ago

Do that and it would no longer be useful as proof of work. Proof of work-i-was-going-to-do-anyway is not useful for securing the ledger.

akvadrako 9y ago

That's incorrect. All that matters is you can't game the system by taking shortcuts or deciding what the problem will be beforehand; the work cannot be even partially computable without knowing the previous block.

spiorf 9y ago
But there is no known function that has these properties and is useful in real world.
- akvadrako 9y ago
  Sure and that puts it in the same camp as PoS and other currently unworkable schemes. A possible way forward; we don't know yet.
Taek 9y ago
No, you are incorrect. The important aspect of proof of work is that it is very expensive to create an alternate history (maybe one where you didn't send $15,000,000 to the exchange, for example). If you are doing useful work, someone can pay for it, and you can use that payment to make an alternate history for free, defeating the security assumption of blockchains. Blockchains only work by probably wasting in order to build a history. If you aren't wasting, then it wasn't expensive to build the history (it was subsidised), and it wouldn't be expensive to build a different history (that one could also be subsidized)
- SilasX 9y ago
  But "socially useful" does not imply saleable (to the bane of venture capitalists everywhere). It's possible for something to provide a social benefit but not make sense for anyone to pay for as a for-profit business because others would get the same benefit and free ride off them. (Hence the problem of public goods in economics.) So if the proof of work is only solving some general research problem, then it might not be feasible to double dip like you've described. That's why primecoin was able to avoid the problem.
  - Taek 9y ago
    Primecoin also ultimately had limited utility. It found the world's largest prime number thousands of times, continually beating it's own record. At some point we had more prime numbers than had mathematical utility. My unprovable guess is that any other non-sellable problem will ultimately have the same outcome. It's interesting and useful for a bit, but when you have a billion dollars of hardware grinding nonstop for years in a row, you eventually exhaust everything interesting about the original problem and then it's back to the same waste you started with.
    - SilasX 9y ago
      Doesn't that mean it worked too well, and we just need to make a Coin with harder and more useful problems?
  - kobeya 9y ago
    There are very few things that are actually useful (socially or otherwise) but don't provide economic incentive. As pointed out by others primecoin isn't really a very good example. A good application to shoot for, if there are any budding cryptographers in the audience, is a ticking timelock encryption. A set of keys known in advance, and each block solves the next key. This would let you encrypt messages into the future, where the cost to decrypt is equal to the cost of minting that many blocks. I've seen partial schemes for this, but no complete ones that would justify implementation. If a full and workable scheme could be devised, I would bet on it replacing sha256 based proof of work, eventually.
    - SilasX 9y ago
      Every public goods problem is mathematical research is a case where the solutions are socially useful but not saleable. The problem (pointed out by the sibling) with primecoin was that it worked too well, such that further solutions were uninteresting and past the point of diminishing returns. Edit: See my here for a model of how NP complete problems could fill the role of you could predict difficulty in advance. There wouldn't be double dipping because the person wanting the answer wouldn't pay both bounties. https://news.ycombinator.com/item?id=15107653 https://news.ycombinator.com/item?id=15107653
- akvadrako 9y ago
  It doesn't matter if the work is profitable because you only need to create an alternate history for a few blocks. If you attack the network you can steal billions - so if you have that much computing power available for your useful work, you can temporarially use it against the block chain. As long as that mining power is available anywhere the chain isn't secure.