As far as I am aware that HS servers need to communicate with 3 points, which are Introduction point, Rendezvous point, and HS directory. So how many Tor relays are there in the circuit between the HS server and these 3 points?
Each Tor circuit has 3 relays: a guard, middle, and exit. A HS server will build a Tor circuit to the Introduction Point, Rendezvous Point, and HS Directory, so there would be 3 relays between the HS Server and any of these 3 points.
When browsing a Hidden Service, your browser and the HS Server each build their own circuit to the Rendezvous Point, so there would be 6 relays between the HS server and client, 7 if you count the Rendezvous Point.
The Hidden Service descriptor is signed with the HS Private Key before being sent to the HS directory. According to the Rendezvous spec 1.4,
Upon receiving a descriptor, the directory server checks the signature, and discards the descriptor if the signature does not match the enclosed public key.
It doesn't specifically say if the descriptor is hashed or encrypted, but if it's signed with the private key, the public key can be used to verify authenticity. The Public Key is then used to encrypt messages to the HS Server, which can then be decrypted with the Private Key.
The Rendezvous Spec talks about encryption in various parts, but it seems to be talking about the actual rendezvous and introduction point, not the HS descriptor.
Thanks for the link, I just read it, and found this paragraph: " the hidden service assembles a hidden service descriptor, containing its public key and a summary of each introduction point, and signs this descriptor with its private key. It uploads that descriptor to a distributed hash table. The descriptor will be found by clients requesting XYZ.onion where XYZ is a 16 character name derived from the service's public key. After this step, the hidden service is set up." Does it mean the "HS descriptor" is encrypted before being send to HSDir or it is in plain text comprising of PK and IP1-3? Sep 23, 2016 at 19:06
More specifically, does the term " signs this descriptor with its private key" mean HS server hashes or encrypts the package(PK-IP1-3) before sending it to HSDir? Sep 23, 2016 at 19:10
1I updated the answer with some (hopefully) useful information. Sep 23, 2016 at 19:38
Just an extra question related to this topic, so can you tell me how many hops are there in the Rendezvous circuit that connects the Client and the HS server? is it a 6-hop or 7-hop citcuit (including the Rendezvous Point)? Sep 25, 2016 at 1:37
1I believe it would be a 7-hop counting the rendezvous point, because there is a 3-node circuit on both sides. Sep 25, 2016 at 3:08