https://blog.torproject.org/introducing-proof-of-work-defense-for-onion-services/ https://blog.torproject.org/introducing-proof-of-work-defens... Tor has simil

https://blog.torproject.org/introducing-proof-of-work-defense-for-onion-services/ https://blog.torproject.org/introducing-proof-of-work-defens... Tor has similarly been using Proof of Work as part of the defense for onion services for around a year and a half now. I’ve also seen some clear net web sites that use PoW to slow down account creation. Some websites will even adjust the difficulty for individual visitors depending on the recent number of sign-ups coming from their IP block. More signups from an IP block -> higher PoW difficulty for anyone from that IP block -> fewer accounts created by anyone in that IP block over a span of time.