http://ttevhjjsjxz6uqqcjkbig5cycd7n7xv7cmd6f5fcvrqaaa7f3bj36wad.onion/technology/security/pow/index.html
(in simple terms) ¶ In order to be effective against DoS attacks, a Proof of Work mechanism must run
before the bulk of server-side computation happens when an Onion Service
connection is established, and to be enabled only if the service is under
stress. With the Proof of Work (PoW) mechanism, the introduction phase for Onion
Service connections is split in two parts: During the first part, A service under load can indicate a level of effort it expect clients
to employ...