> Cynthia Dwork and Moni Naor IIRC Dwork and Naor's work had a trapdoor (which the server used to cheaply validate the challenges) and would be unsuitable for

> Cynthia Dwork and Moni Naor IIRC Dwork and Naor's work had a trapdoor (which the server used to cheaply validate the challenges) and would be unsuitable for any kind of decentralized public system. It's not "proof of work" in the same sense, or arguably proof of work at all to anyone but the server and parties that trust them.