[tor-bugs] #16824 [Tor]: coexistence of client and relay processing on same thread poses traffic confirmation risk

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#16824: coexistence of client and relay processing on same thread poses traffic
confirmation risk
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 Reporter:  starlight  |          Owner:
     Type:  defect     |         Status:  new
 Priority:  normal     |      Milestone:
Component:  Tor        |        Version:
 Keywords:             |  Actual Points:
Parent ID:             |         Points:
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 Analysis presented in bug #16585 demonstrates client circuit formation
 processing perturbs relay cell forwarding in a manner that may be
 susceptible to traffic confirmation analysis.

 With the present code structure it is recommended that simultaneous client
 and relay operation be aggressively discouraged with a new `torrc`
 configuration parameter to inhibit it--default value set to prevent.  In
 addition log warnings should be generated when both client and relay
 functions are allowed to operate concurrently.

 Correct support of simultaneous client and relay function  requires
 segregation of the client function to a separate thread running on a
 different processor core than the relay function.

 Correcting the current client implementation's deficit of transaction
 granularity is unlikely to eliminate the potential for a sophisticated
 advisory to detect perturbation of cell forwarding by client circuit
 creation activity.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16824>
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