http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/rend-spec/rendezvous-protocol.html
Subsequently, the rendezvous point passes RELAY cells, unchanged, from each
of the two circuits to the other. When Alice's OP sends RELAY cells along
the circuit, it authenticates with Df, and encrypts them with the Kf, then
with all of the keys for the ORs in Alice's side of the circuit; and when
Alice's OP receives RELAY cells from the circuit, it decrypts them with the
keys for the ORs in Alice's side of the circuit, then decrypts them...