Hi, all!
Michael Backes, Aniket Kate, and Esfandiar Mohammadi have a paper in submission called, "An Efficient Key-Exchange for Onion Routing". It's meant to be more CPU-efficient than the proposed "ntor" handshake. With permission from Esfandiar, I'm sending a link to the paper here for discussion.
http://www.infsec.cs.uni-saarland.de/~mohammadi/owake.html
What do people think?