Bridge
A bridge is a Tor relay whose address does not appear in the public relay list. It helps where known Tor entry points are blocked. Bridges can be used together with pluggable transports. They are a censorship-circumvention tool, not an extra anonymity guarantee.
Why bridges exist
The Tor directory is public on purpose: every client must know the relays in order to build a circuit. That openness has a downside. Anyone filtering a country’s or an organization’s traffic can download the same list and block every address on it. Bridges solve exactly this by being kept off the public list and distributed only in small portions.
How to get a bridge
Tor Browser ships a set of built-in bridges that can be tried without further steps. If they are not enough, addresses can be requested from the Tor Project’s BridgeDB, and in some regions also by email or a messenger bot. Issuing them in portions is intentional: it makes it harder for a censor to collect the entire pool and block it in one go.
What a bridge does not do
A bridge replaces the Guard Node in the first position of the circuit; the remaining two hops and the encryption stay unchanged. Anonymity toward the destination is neither better nor worse. If not only known Tor addresses are blocked, but the traffic pattern itself is recognized, an inconspicuous address is not enough — then you also need a Pluggable Transport that makes the connection look different.
How the circuit as a whole is built is explained in What is Tor?.
Category: Censorship