Consumer devices have a lot of spare CPU and RAM. So a proof-of-work algorithm which consumes those resources for a minute might work?
If it generates $0.01 for the website owner in that minute, maybe that would work?
Tor has such a feature for denial of service protection.
https://blog.torproject.org/introducing-proof-of-work-defens...
A benefit of a token is you can recycle previous proof of work by using a small amount of Bitcoin, which could be transferred using Lightning. The value could also be transferred back some amount of time after registration given no bad behavior, allowing for larger sums than a cent, which could provide better protection.
If you only consume resources on the client side, then you hope that an attacker thinks "I won't invest $0.01 of resources just to log in here".
If you also transfer the consumed resources to the server, you get an additional benefit: The server thinks "$0.01 is enough to cover the costs of a fake signup".
And the second benefit is probably even better than the first. The server will never really know how cheaply attackers can access resources. But they probably know how much a fake signup costs them.
The drawback is it gets a lot more complex when using a token, because of the additional state, communication, costs and security.
A one shot proof of work can be very simple, but probably not effective enough, given that mobile users likely do not want to wait what may have to be many minutes and drain their battery.
Freezing a cent or a dollar for days seems like a better option. Might very well be that VISA/MasterCard figures this out before the crypto bros build anything usable. It will be far easier to do without decentralization and would also be great to spy on and control people.
Fucking A HN.
For any Juniors using this site, this is exactly what you don't post. Especially if it's just to cathart cynicism. I assure you, Poe's law guarantees this will find it's way into some PM's or exec's mind somewhere.
If the captcha is to prevent overuse of a free trial, then nobody will operate a lot of devices just to get more free trials if the paid version is cheaper than those devices.
If the use case is to improve democracy, then it gets more complicated.
There are exotic solutions like the 'Idena Network'. But sadly I have to admit the best solution I've seen so far is Sam Altman's Worldcoin. Not that I'm a fan, I still hope we can find something better than scanning everyone's eyeball.