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86 lines
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86 lines
3.5 KiB
Plaintext
Filename: 296-expose-bandwidth-files.txt
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Title: Have Directory Authorities expose raw bandwidth list files
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Author: Tom Ritter
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Created: 11-December-2017
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Status: Open
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Ticket: https://trac.torproject.org/projects/tor/ticket/21377
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1. Introduction
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Bandwidth Authorities (bwauths) perform scanning of the Tor Network
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and calculate observed bandwidths for each relay. They produce a bandwidth
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list file that is given to a Directory Authority. The Directory
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Authority uses the bw (bandwidth) value from this file in its vote file
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denoting its view of the bandwidth of the relay.
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After collecting all of the votes from other Authorities, a consensus
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is calculated, and the consensus's view of a relay's speed is
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determined by choosing the low-median value of all the authorities'
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values for each relay.
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Only a single metric from the bandwidth list file is exposed by a
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Directory Authority's vote, however the original file contains
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considerably more diagnostic information about how the bwauth arrives
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at that measurement for that relay.
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For more details, see the bandwidth list file specification in
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bandwidth-file-spec.txt.
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2. Motivation
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The bandwidth list file contains more information than is exposed in the
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overall vote file. This information is useful to debug:
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* anomalies in relays' utilization,
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* suspected bugs in the (decrepit) bwauth code, and
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* the transition to a replacement bwauth implementation.
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Currently, all bwauths expose the bandwidth list file through various (non-
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standard) means, and that file is downloaded (hourly) by a single person
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(as long as his home internet connection and home server is working)
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and archived (with a small amount of robustness.)
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It would be preferable to have this exposed in a standard manner.
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Doing so would no longer require bwauths to run HTTP servers to expose
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the file, no longer require them to take additional manual steps to
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provide it, and would enable public consumption by any interested
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parties. We hope that Collector will begin archiving the files.
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3. Specification
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An authority SHOULD publish the bandwidth list file used to calculate its
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next vote. It SHOULD make the bandwidth list file available whenever the
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corresponding vote is available, at the corresponding URL. (See
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dir-spec for the exact details.)
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It SHOULD make the file available at
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http://<hostname>/tor/status-vote/next/bandwidth.z
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http://<hostname>/tor/status-vote/current/bandwidth.z
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It MUST NOT attempt to send its bandwidth list file in a HTTP POST to
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other authorities and it SHOULD NOT make bandwidth list files from other
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authorities available.
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Clients interested in consuming these documents should download them from
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each authority's:
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* next URL when votes are created. (In the public Tor network, this is
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after HH:50 during normal operation, and after HH:20 during a
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consensus failure.)
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* current URL after the valid-after time in the consensus.
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(After HH:00, and HH:30 during consensus failure.)
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4. Security Implications
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The raw bandwidth list file does not [really: is not believed to] expose
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any sensitive information. All authorities currently make this
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document public already, an example is at
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https://bwauth.ritter.vg/bwauth/bwscan.V3BandwidthsFile
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5. Compatibility
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Exposing the document presents no compatibility concerns.
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Applications that parse the document should follow the bandwidth list file
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specification in bandwidth-file-spec.txt.
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If a new bandwidth list format version is added, the applications MAY need
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to upgrade to that version.
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