[tor-dev] Proposal 176: Proposed version-3 link handshake for Tor

[Nick Mathewson]

On Wed, Sep 21, 2011 at 1:58 PM, Nick Mathewson <nickm at alum.mit.edu> wrote:

I'm thinking of a few more tweaks to this proposal, based on implementation.

Here's one:

> I think on reflection that we should change the TLSSECRETS field from
> optional to required in all AUTHENTICATE cells.  Only relays need to
> send it, after all.

Doing this makes us more secure, at the expense of making it a little
harder for now to write a relay using an inflexible TLS library that
you can't change.

Another change: Previously I had said that every server (including
relays and bridges) should send an AUTH_CHALLENGE cell to say "I'd
like authentication".  In fact, that should only apply to relays:
There is never a point in authenticating to a bridge, right?
Similarly, bridges should only authenticate to their clients, not to
the relays that they're extending to.

So here, I think, are the  right behaviors for the possible
interactions in the v3 protocol now:
  Client connects to bridge:
    C->B: VERSIONS
    B->C: VERSIONS, CERT, NETINFO
    C->B: NETINFO
  Client or bridge connects to relay:
    C->R: VERSIONS
    R->C: VERSIONS, CERT, AUTH_CHALLENGE, NETINFO
    C->R: NETINFO
  Relay connects to relay:
    R1->R2: VERSIONS
    R2->R1: VERSIONS, CERT, AUTH_CHALLENGE, NETINFO
    R1->R2: CERT, AUTHENTICATE, NETINFO

-- 
Nick