I am learning about Tor and Onion routing and I'm trying to compare both services. From the wiki link, I can see that Diffie Hellman (DH) handshake is used and when look into the “tor-design.pdf” for Tor, I see that DH is still used.

Since onion routing has been patented, I can't find any source which leads me to the design of onion routing. Can someone clarify this point about signatures in both services? Links to support it would be welcome.

  • After a quick googling I found this link which led me to this patent. I don't know the difference per se but I imagine Tor would be designed so as not to infringe on the patent. The Wikipedia page provides an overview of OR so you might see the difference between that and Tor if the patent uses difficult language. Moreover I've never heard of the DH exchange being patented, but of course I'm not a lawyer.
    – rath
    Commented Dec 1, 2013 at 18:10
  • We have a Tor site! Yay!
    – rath
    Commented Dec 1, 2013 at 21:57
  • @PR Would you like us to move the question to Tor.SE or perhaps Security.SE?
    – mikeazo
    Commented Dec 4, 2013 at 14:47

1 Answer 1


As far as I can see it from the original onion routing patent, OR uses long term public keys for encrypting messages for onion routers and there is no description of a key exchange.

Tor can be seen as the second generation onion routing (and is intended to have no patent) and besides adding much more features (adding perfect forward secrecy, congestion control, directory servers, integrity checking, configurable exit policies) it uses a technique denoted as telescoping circuits, which on the one hand brings other features (such as forward secrecy) but also helps to circumvent patent issues with the original OR patent (as it does no longer apply the original "long term key" method proposed in the patent).

Basically, the idea of telescoping circuits is that a sender negotiates a short-term session key with each node along a path, and uses this key to encrypt the onion layers. Thereby, Diffie-Hellman is is used for key exchange with the onion routers and the negotiated session keys are AES keys.

You must log in to answer this question.