Exit Balancing Patch

[Roger Dingledine]

On Fri, Jul 27, 2007 at 12:55:15AM -0400, Roger Dingledine wrote:
>  And are there
> better hacks we should be considering

For example, here's another hack we might use: choose guards, weighted
by bandwidth, demanding that they are Fast (top 7/8s of the network)
and Stable (currently top 1/2 of the network by uptime, but hopefully
to be replaced by Proposal 108 [1] sometime), and then when Alice wants
to use a guard, she selects from the first k nodes in her guard list,
adding new ones as needed, where k is computed such that she's choosing
from at least n bytes/s worth of advertised bandwidth.

We could choose n to be x times the yth percental of bandwidth in the
network, e.g. 5 times the 50% mark, or 2 times the 25% mark, such that
the probability of getting many crummy nodes in a row is extremely
small, but we still get the "your list doesn't rotate often" property
we want.

We could add another "but k must be at least 2" exception if we liked,
to avoid picking a huge one first and using it exclusively, but that
doesn't sound so bad actually. Are there any other weird cases we might
want to consider exceptions for?

Of course, all these magic numbers are coming out of nowhere, which
makes me a bit sad, but we are lacking a "principled" solution here.

[1] https://tor.eff.org/svn/trunk/doc/spec/proposals/108-mtbf-based-stability.txt