[toxicFork]

> Friendly Captcha generates a unique crypto puzzle for each visitor. As soon as the user starts filling a form it starts getting solved automatically. Solving it will usually take a few seconds. By the time the user is ready to submit, the puzzle is probably already solved.

What makes this NOT work on a bot machine?

[yomlica8]

It sounds like a proof of work rate limiter similar to something hashcash. I don't think it will stop a bot machine, just make it very expensive to use. Which is actually all regular captchas do anyway.

Whenever this comes up as an alternative to regular captchas I see a lot of push back that we can't do this because it would cost mobile users to much battery power. If that is really such a concern, let the mobile users solve shitty captchas as an alternative and the rest of us use something like this. Mobile users already endure horrible privacy, no easy ad blocking, countless "install our app" popups and a software ecosystem that is infested with dark patterns so I don't see how they would really even notice.

[bastawhiz]

> I don't think it will stop a bot machine, just make it very expensive to use

My phone solves the captcha puzzle in about three seconds. I assume it's working on one core. If you're running this on a server and it's able to do one every, say, two seconds, and you have sixteen cores, that's still about eight per second. At that point, what is this defending against? You're running into API rate limit territory.

The whole point of a captcha is to make it unsolvable for a machine. Not to make it more expensive. Because the bad actors will eventually make it cheap, and then it's not effective anymore. Consider that today, it's often cheaper to farm out CAPTCHA puzzles to a room full of humans on laptops than it is to solve them. Making it a purely computational challenge is almost certainly saving money for the bad actors.

[JohnFen]

> It sounds like a proof of work rate limiter similar to something hashcash. I don't think it will stop a bot machine, just make it very expensive to use

Ah, OK. I was wondering the exact same thing as toxicFork. This makes some sense. It's a shame they don't explain it on their website.

But then the natural followup question: why do they keep mentioning blockchain? What's that bringing to the table? If it's just about soaking up processing time, then surely anything computationally heavy would do the trick, so why include something that would set off some people's alarm bells?

[hot_gril]

I really think it's meant to awe the business customer with a slick-looking demo, along with assurances that it's "made in Europe, GDPR-compliant, and proven accessible" rather than actually doing the job of a captcha. Sorry to be cynical, but it's oversimplifying the problem and just doesn't work (see below).

[dogma1138]

Nothing, most JS challenges simply rely on the headless browser not executing the JS or that the delay & computational cost would be enough to render most bot attacks ineffective.

[jart]

A better question is why you can't just use a token bucket rather than mining bitcoins on your client's phone wasting their battery.

[Szpadel]

because bots use hundreds IP addresses assigned to the same system, if you have 5r/s from 10k IP addresses it adds up if you require computational power you force them to invest money in hardware and potentially make it unprofitable