A Tor hidden service never opens a listening port the public internet can route to. Instead it reaches out to a small set of relays it picks as Introduction Points and keeps a standing 3‑hop circuit open to each one, then publishes a signed descriptor (list of intro points + a public key) to the hashed DHT (HSDirs), indexed by its own address.
v3 address = base32( pubkey_ed25519 ‖ checksum ‖ version ) + ".onion"
checksum = H(".onion checksum" ‖ pubkey ‖ version)[0:2]
Because the address is a hash of the service's public key, it is self-certifying — there is no CA, no DNS, nothing to phish or hijack. Any client can verify it is really talking to the key-holder just from the address string.
To connect, a client also builds a 3‑hop circuit to one of the published intro points and sends an INTRODUCE1 cell naming a Rendezvous Point (RP) — an ordinary relay the client itself chose and built a separate 3‑hop circuit to, together with a one-time cookie. The service then builds its own 3‑hop circuit to that same RP and presents the cookie. The RP simply splices the two circuits together; it forwards Tor-encrypted cells and never sees plaintext or either party's cell content.
- Mutual anonymity — of the ~2 circuits × 3 hops plus the intro point and RP (≈8 relays total), not one ever learns both the client's and the service's real IP address. That is the property this schematic visualizes, not the entry/exit traffic-correlation attack a global adversary could mount.
- Redundancy — a service normally publishes several intro points; if an adversary seizes or blocks one, clients simply retry through another as long as at least one is alive.
- Unlinkability — the client picks a fresh Rendezvous Point for every new session, so two visits cannot be linked to each other through the RP.
- Regenerating the identity key changes the address entirely — v2 real-world incidents (short, brute-forceable v2 addresses) are why Tor moved to the longer, cryptographically strong v3 scheme shown here.
This 2D companion renders the exact same relay topology and session state machine as the 3D version, projected flat onto the circuit-diagram plane — drag to pan, scroll or pinch to zoom.