Comment by fluoridation
3 days ago
>An hour of a server CPU costs $0.01. How much is an hour of your time worth?
That's irrelevant. A human is not going to be solving the challenge by hand, nor is the computer of a legitimate user going to be solving the challenge continuously for one hour. The real question is, does the challenge slow down clients enough that the server does not expend outsized resources serving requests of only a few users?
>Even if the attacker is no better at solving the challenge than your browser is, there's no way to tune the monetary cost to be even in the ballpark to the cost imposed to the legitimate users.
No, I disagree. If the challenge takes, say, 250 ms on the absolute best hardware, and serving a request takes 25 ms, a normal user won't even see a difference, while a scraper will see a tenfold slowdown while scraping that website.
The problem with proof-of-work is many legitimate users are on battery-powered, 5-year-old smartphones. While the scraping servers are huge, 96-core, quadruple-power-supply beasts.
The human needs to wait for their computer to solve the challenge.
You are trading something dirt-cheap (CPU time) for something incredibly expensive (human latency).
Case in point:
> If the challenge takes, say, 250 ms on the absolute best hardware, and serving a request takes 25 ms, a normal user won't even see a difference, while a scraper will see a tenfold slowdown while scraping that website.
No. A human sees a 10x slowdown. A human on a low end phone sees a 50x slowdown.
And the scraper paid one 1/1000000th of a dollar. (The scraper does not care about latency.)
That is not an effective deterrent. And there is no difficulty factor for the challenge that will work. Either you are adding too much latency to real users, or passing the challenge is too cheap to deter scrapers.
>No. A human sees a 10x slowdown.
For the actual request, yes. For the complete experience of using the website not so much, since a human will take at least several seconds to process the information returned.
>And the scraper paid one 1/1000000th of a dollar. (The scraper does not care about latency.)
The point need not be to punish the client, but to throttle it. The scraper may not care about taking longer, but the website's operator may very well care about not being hammered by requests.
But now I have to wait several seconds before I can even start to process the webpage! It's like the internet suddenly became slow again overnight.
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A proof of work challenge does not throttle the scrapers at steady state. All it does is add latency and cost to the first request.
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