  Onion addresses encode their own public key. They are thus
self-authenticating, one of the security and privacy advantages of onion
services, which are typically accessed via Tor Browser. Because of the mostly
random-looking appearance of onion addresses, a number of onion discovery
mechanisms have been created to permit routing to an onion address associated
with a more meaningful URL, such as a registered domain name.
  We describe novel vulnerabilities engendered by onion discovery mechanisms
recently introduced by Tor Browser that facilitate hijack and tracking of user
connections. We also recall previously known hijack and tracking
vulnerabilities engendered by use of alternative services that are facilitated
and rendered harder to detect if the alternative service is at an onion
address.
  Self-authenticating traditional addresses (SATAs) are valid DNS addresses or
URLs that also contain a commitment to an onion public key. We describe how the
use of SATAs in onion discovery counters these vulnerabilities. SATAs also
expand the value of onion discovery by facilitating self-authenticated access
from browsers that do not connect to services via the Tor network.
