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+Filename: 177-flag-abstention.txt
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+Title: Abstaining from votes on individual flags
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+Author: Nick Mathewson
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+Created: 14 Feb 2011
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+Status: Draft
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+
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+Overview:
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+
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+ We should have a way for authorities to vote on flags in
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+ particular instances, without having to vote on that flag for all
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+ servers.
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+
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+Motivation:
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+
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+ Suppose that the status of some router becomes controversial, and
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+ an authority wants to vote for or against the BadExit status of
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+ that router. Suppose also that the authority is not currently
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+ voting on the BadExit flag. If the authority wants to say that
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+ the router is or is not "BadExit", it cannot currently do so
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+ without voting yea or nay on the BadExit status of all other
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+ routers.
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+
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+ Suppose that an authority wants to vote "Valid" or "Invalid" on a
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+ large number of routers, but does not have an opinion on some of
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+ them. Currently, it cannot do so: if it votes for the Valid flag
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+ anywhere, it votes for it everywhere.
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+
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+Design:
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+
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+ We add a new line "extra-flags" in directory votes, to appear
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+ after "known-flags". It lists zero or more flags that an
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+ authority has occasional opinions on, but for which the authority
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+ will usually abstain. No flag may appear in both extra-flags and
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+ known-flags.
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+
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+ In the router-status section for each directory vote, we allow an
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+ optional "s2" line to appear after the "s" line. It contains
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+ zero or more flag votes. A flag vote is of the form of one of
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+ "+", "-", or "/" followed by the name of a flag. "+" denotes a
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+ yea vote, and "-" denotes a nay vote, and "/" notes an
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+ abstention. Authorities may omit most abstentions, except as
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+ noted below. No flag may appear in an s2 line unless it appears
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+ in the known-flags or extra-flags line.We retain the rule that no
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+ flag may appear in an s line unless it appears in the known-flags
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+ line.
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+
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+ When using an appropriate consensus method to vote, we use these
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+ new rules to determine flags:
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+
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+ A flag is listed in the consensus if it is in the known-flags
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+ section of at least one voter, and in the known-flags or
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+ extra-flags section of at least three voters (or half the
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+ authorities, whichever set is smaller).
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+
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+ A single authority's vote for a given flag on a given router is
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+ interpreted as follows:
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+
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+ - If the authority votes +Flag or -Flag or /Flag in the s2 line for
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+ that router, the vote is "yea" or "nay" or "abstain" respectively.
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+ - Otherwise, if the flag is listed on the "s" line for the
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+ router, then the vote is "yea".
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+ - Otherwise, if the flag is listed in the known-flags line,
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+ then the vote is "nay".
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+ - Otherwise, the vote is "abstain".
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+
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+ A router is assigned a flag in the consensus iff the total "yeas"
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+ outnumber the total "nays".
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+
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+ As an exception, this proposal does not affect the behavior of
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+ the "Named" and "Unnamed" flags; these are still treated as
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+ before. (An authority can already abstain from a single naming
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+ decision by not voting Named on any router with a given name.)
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+
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+Examples:
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+
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+ Suppose that it becomes important to know which Tor servers are
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+ operated by burrowing marsupials. Some authority operators
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+ diligently research this question; others want to vote about
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+ individual routers on an ad hoc basis when they learn about a
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+ particular router's being e.g. located underground in New South
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+ Wales.
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+
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+ If an authority usually has no opinions on the RunByWombats flag,
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+ it should list it in the "extra-flags" of its votes. If it
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+ occasionally wants to vote that a router is (or is not) run by
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+ wombats, it should list "s2 +RunByWombats" or "s2 -RunByWombats"
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+ for the routers in question. Otherwise it can omit the flag from
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+ its s and s2 lines entirely.
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+
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+ If an authority usually has an opinion on the RunByWombats flag,
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+ but wants to abstain in some cases, it should list "RunByWombats"
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+ in the "known-flags" part of its votes, and include
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+ "RunByWombats" in the s line for every router that it believes is
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+ run by wombats. When it wants to vote that a router is not run
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+ by wombats, it should list the RunByWombats flag in neither the s
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+ nor the s2 line. When it wants to abstain, it should list "s2
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+ /RunByWombats".
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+
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+ In both cases, when the new consensus method is used, a router
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+ will get listed as "RunByWombats" if there are more authorities
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+ that say it is run by wombats than there are authorities saying
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+ it is not run by wombats. (As now, "no" votes win ties.)
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+
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+
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