> A possibly better approach is to use money to create deposits. There is a protocol that allows bitcoins to be sacrificed to miners fees, letting you prove that you threw money away by signing challenges with the keys that did so.
This wouldn't work, because a miner can easily pay himself any amount of bitcoins that he has saved up in fees, and include this transaction in his own block (not broadcasting it). Thus he can basically create these "deposits" for free, and sell them for a profit.
That's the thing: whatever you try as a counter-measure, you always come back to money: in the above scenario, money would replace "deposits" because "deposits" would just be sold on the open market for money. Proof-of-work becomes money: if something important requires proof-of-work, you can be sure that a web app would surface that performs proof-of-work in exchange for money.
It always comes back to money, because whatever restriction you put on something, whether it be "pay fee to Bitcoin miners", "Solve proof-of-work puzzle", or something else entirely, these things will always end up being sold for money in an efficient market, because of the increased efficiency of division of labor: why should I use my inefficient smartphone to calculate proof-of-work, when I can pay a service with custom ASICs to do the job for me at a fraction of the cost?
As far as I can see, the only alternative that can work besides money is something that cannot be sold for money. And I can't come up with anything that fits this requirement.
Not sure why you were downvoted. While I may or may not agree with your opinion I think you expressed it in a completely reasonable fashion and made a number of interesting points.
But your smartphone is something you already have. If it takes ten seconds then you already paid for those ten seconds when you brought it.
Of course spammers can buy their services but when the price for normal sending is effectively free for normal users you can jack up the price for spammers to make it too expensive for them.
A nice benefit is that it forces sites to use something other than email, such as RSS, since they can't afford to send newsletters anymore.
Maybe, but the performance difference between a power-strapped smartphone CPU and an ASIC tailored for the specific task is so massive I doubt you could make it expensive enough for the latter while maintaining a reasonable experience for the former.
I see two solutions to it. First: have the phone include a chip specifically for doing this type of work. Second: make the calculation such that it cannot be performed faster on cheap hardware specialized for the task. I believe that is the peppery of scrypt, and the reason why we do not see LiteCoin ASIC's yet.
having everything come back to money is a good thing though - a user can afford to pay e.g. 1 microdollar per email sent but if a spammer is sending 10 million emails a day, they can't afford that level of operational expense.
It's sufficient to just destroy the bitcoins by sending them to a non-existent address. Alternatively, they could be donated to a third party such as a charity or an open-source software foundation.
This wouldn't work, because a miner can easily pay himself any amount of bitcoins that he has saved up in fees, and include this transaction in his own block (not broadcasting it). Thus he can basically create these "deposits" for free, and sell them for a profit.
That's the thing: whatever you try as a counter-measure, you always come back to money: in the above scenario, money would replace "deposits" because "deposits" would just be sold on the open market for money. Proof-of-work becomes money: if something important requires proof-of-work, you can be sure that a web app would surface that performs proof-of-work in exchange for money.
It always comes back to money, because whatever restriction you put on something, whether it be "pay fee to Bitcoin miners", "Solve proof-of-work puzzle", or something else entirely, these things will always end up being sold for money in an efficient market, because of the increased efficiency of division of labor: why should I use my inefficient smartphone to calculate proof-of-work, when I can pay a service with custom ASICs to do the job for me at a fraction of the cost?
As far as I can see, the only alternative that can work besides money is something that cannot be sold for money. And I can't come up with anything that fits this requirement.