Proposal 105 (handshake revision) needs more thought

Nick Mathewson nickm at
Wed Mar 21 04:27:53 UTC 2007

On Sun, Mar 11, 2007 at 06:55:34PM -0400, Roger Dingledine wrote:
> Hi folks,
> Proposal 105 looks like a nice start. For those of you who haven't
> already read it, go look at
> I've got a few questions/comments, based on trying to write the
> "Advertising versions in routerdescs and networkstatuses" section.
> Here's some new text, that I'm afraid mainly raises questions.

I've written a spec addendum for that section and checked it in; it
tries to take a position on these questions.

I've taken the position of "put in the Tor version as well as the
protocol version", since it seems generally more useful.  (In theory,
we could eventually eliminate listing the Tor version.  However,
you've convinced me that practice is not likely to converge with
theory in this case.)

>    Should we just add more arguments to that same line (ending up with
>    "Tor Link 5 Circuit 6") or do we want multiple "v" lines?
>    I don't see any strong arguments either way.

I've gone with one v line.  (That's my favorite color for the bikeshed.)

`>    If servers support multiple link versions (e.g. they would include
>    several in their VERSIONS cell), do we list all of them here, or
>    just the latest, or ...? My guess is we should list just the latest,
>    at least until the situation is common where that isn't useful to
>    most clients.

On further though, I'm pretty sure that "list them all" is best; the
upgrade path from "list the latest" to "list them all" isn't clear: if
we ever want to be able to "list them all", then clients would need to
be able to parse multi-item lists from day one. Compression will make
"list them all" about as cheap as "list the latest", so I'm not too
concerned with the space.  On the other hand, "list the latest" would
become non-useful the moment we wanted to deprecate a protocol, or the
moment somebody did an independent server implementation  that only
supported the latest protocol version.

Nick Mathewson
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