Glossary

                               The Tor Project

Note: This document aims to specify terms, notations or phrases related
to Tor and The Tor Project.

This glossary is not a design document; it is only a reference.

0. Preliminaries

      The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
      NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
      "OPTIONAL" in this document are to be interpreted as described in
      RFC 2119.

1.0 Commonly used Tor configuration terms

   ORPort  - Onion Router Port
   DirPort - Directory Port

2.0 Tor network components

   2.1 Relay, aka OR (onion router)

    2.1.1 Specific roles

      Exit relay: The final hop in an exit circuit before traffic leaves
      the Tor network to connect to external servers.

      Non-exit relay: Relays which send and receive traffic only to
      other Tor relays.

      Entry relay: The first hop in a Tor circuit. Can be either a guard
      relay or a bridge, with bridges taking precedant.

      Guard relay: Currently only used as entry relays. Guard relays
      are rotated more slowly to prevent enumeration attacks.

      Bridge: A relay intentionally not listed in the public Tor
      consensus, with the purpose of circumventing entities (such as
      governments or ISPs) seeking to block clients from using Tor.
      Currently, bridges are used only as entry relays.

      Directory cache: On bootstrap, clients will query a directory
      authority for the latest consensus. However, later consensus
      fetches can be made to directory caches, which can be any relay in
      the network.

      Rendezvous point: A relay connecting a client to a hidden service.
      Each party will build a three-hop circuit, meeting at the
      rendezvous point.

   2.2 Client, aka OP (onion proxy)

   2.3 Authorities:

    Directory Authority: Nine total in the Tor network, operated by
    trusted individuals. Directory authorities define and serve the
    consensus document, i.e, the "state of the network," which contains
    router statuses for all relays currently in the network. Directory
    authorities also serve server descriptors, extra info documents,
    microdescriptors, and the microdescriptor consensus,

    Bridge Authority: One total. Similar in responsibility to directory
    authorities, but for bridges.

    Fallback Directory Mirror: On bootstrap, a client will first attempt
    to fetch the consensus document from fallback directory mirrors,
    a relay selected for this role due to its stability and longevity
    on the network.

   2.4 Hidden Service:

   A hidden service is a server that will only accept incoming
   connections via the hidden service protocol. Connection
   initiators will not be able to learn the IP address of the hidden
   service, allowing the hidden service to receive incoming connections,
   serve content, etc, while preserving its location anonymity.

   2.5 Circuit:

   An established path through the network, where cryptographic keys
   are negotiated using the ntor protocol or TAP (Tor Authentication
   Protocol (deprecated) with each hop. Circuits can differ in length
   depending on their purpose. See also Leaky Pipe Topology.

    Origin Circuit -

    Exit Circuit: A circuit which connects clients to destinations
    outside the Tor network. For example, if a client wanted to visit
    duckduckgo.com, this connection would require an exit circuit.

    Internal Circuit: A circuit whose traffic never leaves the Tor
    network. For example, a client could connect to a hidden service via
    an internal circuit.

   2.6 Edge connection:

   2.7 Consensus: The state of the Tor network, published every hour,
     decided by a vote from the network's directory authorities. Clients
     fetch the consensus from directory authorities, fallback
     directories, or directory caches.

   2.8 Descriptor: Each descriptor represents information about one
    relay in the Tor network. The descriptor includes the relay's IP
    address, public key fingerprint, along with other data. Relays send
    descriptors to directory authorities, who will vote and publish a
    summary of them in the network consensus.

3.0 Tor network protocols
   Link handshake
   Circuit handshake
   Hidden Service Protocol
   Directory Protocol


4.0 General network definitions

   Leaky Pipe Topology: The ability for packets to be addressed to any
   hop in the path of a circuit. In Tor, the destination hop is
   determined by using the recognized field of relay cells.

   Stream: In the Tor network specifically, TCP streams are multiplexed
   over circuits.

   TLS connection: All pairwise connections in the Tor network are made
   over TLS.