http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/proposals/192-store-bridge-information.html
This is already a problem for the Bridge
lines in a user's configuration file, but by storing more information
about bridges some timings can be deduced.
Another risk is that this allows long-term tracking of users when the
set of bridges a user knows about is known to the attacker, and the set
is unique.