http://ttevhjjsjxz6uqqcjkbig5cycd7n7xv7cmd6f5fcvrqaaa7f3bj36wad.onion/technology/security/pow/index.html
Many connection requests, each one with
its own puzzle solution, requires an increasing amount of computing resources,
up to the point that the attacker exhaust their resources or have to invest
more and more with diminishing chance of success. A legitimate user, on the other hand, needs one or only a few connections to
the server, so she may be willing to expend computing resources to provide a
solution that has an effort higher enough to get priority over the attacker
connections,...