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+Filename: 147-prevoting-opinions.txt
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+Title: Eliminate the need for v2 directories in generating v3 directories
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+Version: $Revision$
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+Last-Modified: $Date$
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+Author: Nick Mathewson
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+Created: 2-Jul-2008
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+Status: Open
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+
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+Overview
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+
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+ We propose a new v3 vote document type to replace the role of v2
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+ networkstatus information in generating v3 consensuses.
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+
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+Motivation
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+
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+ When authorities vote on which descriptors are to be listed in the
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+ next consensus, it helps if they all know about the same descriptors
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+ as one another. But a hostile, confused, or out-of-date server may
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+ upload a descriptor to only some authorities. In the current v3
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+ directory design, the authorities don't have a good way to tell one
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+ another about the new descriptor until they exchange votes... but by
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+ the time this happens, they are already committed to their votes,
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+ and they can't add anybody they learn about from other authorities
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+ until the next voting cycle. That's no good!
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+
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+ The current Tor implementation avoids this problem by having
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+ authorities also look at v2 networkstatus documents, but we'd like
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+ in the long term to eliminate these, once 0.1.2.x is obsolete.
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+
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+Design:
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+
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+ We add a new value for vote-status in v3 consensus documents in
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+ addition to "consensus" and "vote": "opinion". Authorities generate
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+ and sign an opinion document as if they were generating a vote,
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+ except that they send it to one another earlier than they send
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+ votes.
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+
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+ Authorities don't need to generate more than one opinion document
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+ per voting interval, but may. They should send it to the other
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+ authorities they know about, at the regular vote upload URL, before
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+ the authorities begin voting, so that enough time remains for the
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+ authorities to fetch new descriptors.
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+
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+ Upon receiving an opinion document, authorities scan it for any
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+ descriptors that:
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+ - They might accept.
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+ - Are for routers they don't know about, or are published more
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+ recently than any descriptor they have for that router.
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+ Authorities then begin downloading such descriptors from authorities
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+ that claim to have them.
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+
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+ Authorities MAY cache opinion documents, but don't need to.
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+
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+
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Nick Mathewson