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- Filename: 147-prevoting-opinions.txt
- Title: Eliminate the need for v2 directories in generating v3 directories
- Version: $Revision$
- Last-Modified: $Date$
- Author: Nick Mathewson
- Created: 2-Jul-2008
- Status: Accepted
- Target: 0.2.1.x
- Overview
- We propose a new v3 vote document type to replace the role of v2
- networkstatus information in generating v3 consensuses.
- Motivation
- When authorities vote on which descriptors are to be listed in the
- next consensus, it helps if they all know about the same descriptors
- as one another. But a hostile, confused, or out-of-date server may
- upload a descriptor to only some authorities. In the current v3
- directory design, the authorities don't have a good way to tell one
- another about the new descriptor until they exchange votes... but by
- the time this happens, they are already committed to their votes,
- and they can't add anybody they learn about from other authorities
- until the next voting cycle. That's no good!
- The current Tor implementation avoids this problem by having
- authorities also look at v2 networkstatus documents, but we'd like
- in the long term to eliminate these, once 0.1.2.x is obsolete.
- Design:
- We add a new value for vote-status in v3 consensus documents in
- addition to "consensus" and "vote": "opinion". Authorities generate
- and sign an opinion document as if they were generating a vote,
- except that they generate opinions earlier than they generate votes.
- Authorities don't need to generate more than one opinion document
- per voting interval, but may. They should send it to the other
- authorities they know about, at the regular vote upload URL, before
- the authorities begin voting, so that enough time remains for the
- authorities to fetch new descriptors.
- Additionally, authories make their opinions available at
- http://<hostname>/tor/status-vote/next/opinion.z
- and download opinions from authorities they haven't heard from in a
- while.
- Authorities MAY generate opinions on demand.
- Upon receiving an opinion document, authorities scan it for any
- descriptors that:
- - They might accept.
- - Are for routers they don't know about, or are published more
- recently than any descriptor they have for that router.
- Authorities then begin downloading such descriptors from authorities
- that claim to have them.
- Authorities MAY cache opinion documents, but don't need to.
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