torspec/proposals/150-exclude-exit-nodes.txt

Filename: 150-exclude-exit-nodes.txt
Title: Exclude Exit Nodes from a circuit
Author: Mfr
Created: 2008-06-15
Status: Closed
Implemented-In: 0.2.1.3-alpha

Overview

   Right now, Tor users can manually exclude a node from all positions
   in their circuits created using the directive ExcludeNodes.
   This proposal makes this exclusion less restrictive, allowing users to
   exclude a node only from the exit part of a circuit.

Motivation

   This feature would Help the integration into vidalia (tor exit
   branch) or other tools, of features to exclude a country for exit
   without reducing circuits possibilities, and privacy.  This feature
   could help people from a country were many sites are blocked to
   exclude this country for browsing, giving them a more stable
   navigation.  It could also add the possibility for the user to
   exclude a currently used exit node.

Implementation

   ExcludeExitNodes is similar to ExcludeNodes except it's only
   the exit node which is excluded for circuit build.

   Tor doesn't warn if node from this list is not an exit node.

Security implications:

   Open also possibilities for a future user bad exit reporting

Risks:

   Use of this option can make users partitionable under certain attack
   assumptions.  However, ExitNodes already creates this possibility,
   so there isn't much increased risk in ExcludeExitNodes.

   We should still encourage people who exclude an exit node because
   of bad behavior to report it instead of just adding it to their
   ExcludeExit list.  It would be unfortunate if we didn't find out
   about broken exits because of this option.  This issue can probably
   be addressed sufficiently with documentation.