2captcha-php VS crypto-puzzle

> The current price for solving a js captcha is $3/1000 https://2captcha.com/ . The cost of cpu time for your PoW captcha is probably much lower.

The cheapest AWS instance I can find with a dedicated CPU costs $0.000565 per second. So running four cores for two seconds already makes it more expensive — and much less effort and time for a human to solve than a traditional CAPTCHA.

> It might stop the really low effort attacks of people who are spamming billions of pages where the cpu time becomes expensive, but i don't think the ecconomics work for most scenarios.

How are regular CAPTCHAs any different if they cost $0.003 for an attacker to solve?

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Funnily enough I've recently implemented [0] a little proof-of-work generator (or more specifically a time-lock puzzle [1] generator), which is the base building block on top which something like this can be built.

It's a very cool idea imo, you generate a cryptographic puzzle that's cheap for you to make, cheap for you to verify if its solved, and potentially cheap-enough for legitimate users to solve, but expensive-enough that users making too many requests would find solving them prohibitively expensive.

I wish something like this was bolted onto email protocols, it would just cost more to be a spammer than it'd be worth it.

Interesting how mCaptcha seems based on sha256, I don't know enough but it would be worth checking how much the algorithm can be sped up with (already existing) dedicated ASICs, if the attacker can solve the puzzle like 10000x faster than normal users you just can't crank the difficulty of the puzzle high enough and for motivated attackers this becomes basically useless. Basing this of on repeated squarings, like the RSW paper on time-lock puzzles did, seems potentially better.

[0]: https://github.com/fabiospampinato/crypto-puzzle

Nice! I had written a little algorithm that one could use to implement something like this (maybe interesting if you want to understand how it could work): https://github.com/fabiospampinato/crypto-puzzle

I think there's something to this, it costs you next to nothing to generate these puzzles and get a guaranteed, tunable, slowdown factor on attackers (or cost increase for them I guess).