The Bridge Authority is a simple but essential piece of the Tor Network. Unlike the other directory authorities, the Bridge Authority does not get a vote in Tor’s consensus protocol. Instead, it serves to aggregate relay descriptors which Tor Bridges send to it, checking their cryptographic validity and testing that the Bridges’ ORPorts within these descriptors are reachable.
It then sends these descriptors to BridgeDB, which does all the deduplication, cryptographic signature verification (again), stability calculations, pluggable transport argument validation, assignment into the hashring of each Bridge distribution mechanism, and finally distributing the Bridges to Tor clients.