Filename: 107-uptime-sanity-checking.txt
Title: Uptime Sanity Checking
Author: Kevin Bauer & Damon McCoy
Created: 8-March-2007
Status: Closed
Implemented-In: 0.2.0.x

Overview:

   This document describes how to cap the uptime that is used when computing
   which routers are marked as stable such that highly stable routers cannot
   be displaced by malicious routers that report extremely high uptime
   values.

   This is similar to how bandwidth is capped at 1.5MB/s.

Motivation:

   It has been pointed out that an attacker can displace all stable nodes and
   entry guard nodes by reporting high uptimes. This is an easy fix that will
   prevent highly stable nodes from being displaced.

Security implications:

   It should decrease the effectiveness of routing attacks that report high
   uptimes while not impacting the normal routing algorithms.

Specification:

  So we could patch Section 3.1 of dir-spec.txt to say:

   "Stable" -- A router is 'Stable' if it is running, valid, not
   hibernating, and either its uptime is at least the median uptime for
   known running, valid, non-hibernating routers, or its uptime is at
   least 30 days. Routers are never called stable if they are running
   a version of Tor known to drop circuits stupidly.  (0.1.1.10-alpha
   through 0.1.1.16-rc are stupid this way.)

Compatibility:

   There should be no compatibility issues due to uptime capping.

Implementation:

   Implemented and merged into dir-spec in 0.2.0.0-alpha-dev (r9788).

Discussion:

   Initially, this proposal set the maximum at 60 days, not 30; the 30 day
   limit and spec wording was suggested by Roger in an or-dev post on 9 March
   2007.

   This proposal also led to 108-mtbf-based-stability.txt