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55 lines
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55 lines
2.1 KiB
Plaintext
Filename: 207-directory-guards.txt
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Title: Directory guards
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Author: Nick Mathewson
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Created: 10-Oct-2012
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Status: Closed
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Target: 0.2.4.x
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Motivation:
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When we added guard nodes to resist profiling attacks, we made it so
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that clients won't build general-purpose circuits through just any
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node. But clients don't use their guard nodes when downloading
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general-purpose directory information from the Tor network. This
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allows a directory cache, over time, to learn a large number of IPs
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for non-bridge-using users of the Tor network.
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Proposal:
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In the same way as they currently pick guard nodes as needed, adding more
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guards as those nodes are down, clients should also pick a small-ish set
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of directory guard nodes, to persist in Tor's state file.
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Clients should, as much as possible, use their regular guards as their
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directory guards.
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When downloading a regular directory object (that is, not a hidden
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service descriptor), clients should prefer their directory guards
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first. Then they should try more directories from a recent consensus
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(if they have one) and pick one of those as a new guard if the
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existing guards are down and a new one is up. Failing that, they
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should fall back to a directory authority (or a directory source, if
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those get implemented-- see proposal 206).
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If a client has only one directory guard running, they should add new
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guards and try them, and then use their directory guards to fetch multiple
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descriptors in parallel.
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Open questions and notes:
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What properties does a node need to be a suitable directory guard?
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If we require that it have the Guard flag, we'll lose some nodes:
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only 74% of the directory caches have it (weighted by bandwidth).
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We may want to tune the algorithm used to update guards.
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For future-proofing, we may want to have the DirCache flag from 185
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be the one that nodes must have in order to be directory guards. For
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now, we could have authorities set it to Guard && DirPort!=0, with a
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better algorithm to follow. Authorities should never get the
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DirCache flag.
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