[tor-bugs] #4124 [Tor Bridge]: Bridges should use create_fast cells for the first hop of their circuits

[Tor Bug Tracker & Wiki]

#4124: Bridges should use create_fast cells for the first hop of their circuits
------------------------+---------------------------------------------------
 Reporter:  arma        |          Owner:                    
     Type:  defect      |         Status:  new               
 Priority:  major       |      Milestone:  Tor: 0.2.2.x-final
Component:  Tor Bridge  |        Version:                    
 Keywords:              |         Parent:                    
   Points:              |   Actualpoints:                    
------------------------+---------------------------------------------------
 A friendly anonymous user commented on #4115 that bridges can be
 distinguished by whether they use a create cell or create_fast cell. Once
 we fix #4115 it will be even more straightforward to distinguish.

 {{{
 should_use_create_fast_for_circuit(origin_circuit_t *circ)
 {
   or_options_t *options = get_options();
   tor_assert(circ->cpath);
   tor_assert(circ->cpath->extend_info);

   if (!circ->cpath->extend_info->onion_key)
     return 1; /* our hand is forced: only a create_fast will work. */
   if (!options->FastFirstHopPK)
     return 0; /* we prefer to avoid create_fast */
   if (server_mode(options)) {
     /* We're a server, and we know an onion key. We can choose.
      * Prefer to blend in. */
     return 0;
   }

   return 1;
 }
 }}}

 Bridge-detector example:
 {{{
 if (or_circ && !or_circ->is_first_hop && rh.command ==
 RELAY_COMMAND_BEGIN_DIR) {
   /* non-mirror relay detected or bridge, filter it by consensus. */
 }}}

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/4124>
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