Filename: 107-uptime-sanity-checking.txt Title: Uptime Sanity Checking Version: $Revision$ Last-Modified: $Date$ 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