[tor-dev] Proposal 178: Require majority of authorities to vote for consensus parameters

Nick Mathewson nickm at freehaven.net
Wed May 4 00:49:39 UTC 2011

On Mon, May 2, 2011 at 5:23 AM, Sebastian Hahn <hahn.seb at web.de> wrote:
> On Mar 2, 2011, at 8:06 AM, Nick Mathewson wrote:
>> On Tue, Feb 22, 2011 at 1:34 AM, Sebastian Hahn <hahn.seb at web.de> wrote:
>>> Design:
>>> When the consensus is generated, the directory authorities ensure that
>>> a param is only included in the list of params if at least half of the
>>> total number of authorities votes for that param. The value chosen is
>>> the low-median of all the votes. We don't mandate that the authorities
>>> have to vote on exactly the same value for it to be included because
>>> some consensus parameters could be the result of active measurements
>>> that individual authorities make.
>> This is possibly bikeshed, but I would suggest that instead of
>> requiring half of  existing authorities to vote on a particular
>> parameter, we require 3 or more to vote on it. (As a degenerate case,
>> fall back to "at least half" if there are fewer than 6 authorities in
>> the clique.)
> Hrm. I'm not too happy with this,

My rationale was that in practice, it's a pain in practice to try to
get more than 3 or so authority operators to try out an experimental
parameter in a timely basis.  If the set of authority operators ever
grows, getting half of the ops to tweak a parameter in a hurry will
get even harder.

> unless we also include a way for a
> majority of authorities to prevent voting on that parameter altogether.

What if we say that as a matter of design, there should always be, for
each parameter, a value that's semantically equivalent to the absence
of the parameter?  That way a majority of authorities can "turn off"
any parameter without any additional machinery during the vote.


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