Onion routing

[Ulf Möller]

To protect against timing analysis, Onion routing uses encrypted and
padded links, and the connection between the user and his local onion
router is assumed to be secure.

Obviously, padding offers protection against external adversaries
only.  The onion routers themselves know when an anonymous connection
is opened, how much data is transferred, and when it is closed.  So in
contrast to the mix net (where it is sufficient to use one honest mix
in a chain), honest onion routers that are used between two
cooperating onion routers do not offer additional protection.

Onion routers have a fixed number of neighbours.  If the first onion
router does not have any honest neighbours, there is no anonymity.
Generally, the maximal connected component of honest onion routers
forms the anonymity set.

Does that mean that every onion router needs to maintain many
encrypted links, or is there a more efficient solution?