Date Added: Jul 2011
Onion routing is the most common anonymous communication channel. Usually onion routing is specified through asymmetric cipher and thus is inefficient. In Tor (the second generation onion router), it is suggested to employ symmetric cipher to encrypt the packets in onion routing. Obviously, symmetric cipher is much more efficient than the asymmetric cipher employed in the original onion routing. However, whether this idea can really work depends on whether an efficient (both in computation and communication) key generation and exchange mechanism can be designed for the symmetric cipher to employ. The suggestion in Tor is simple and it is a direct employment of Diffie-Hellman handshake to generate the secret keys for the routers' symmetric cipher.