[tor-dev] Reg : using the keep alive messages

Sambuddho Chakravarty sc2516 at columbia.edu
Mon Jun 27 19:50:22 UTC 2011

Sorry about the typo..I meant which is the relevant part of the code which I
can begin looking into if I want to inject RELAY_DROP cells in a circuit in
forward direction (from the OP towards the exit) and backward direction
(from exit to OP).


On Fri, Jun 24, 2011 at 8:36 PM, Sambuddho Chakravarty
<sc2516 at columbia.edu>wrote:

>  Which is the relevant part of the that should I look into for injecting
> such cells in streams ?
> Thanks
> Sambuddho
> On Thu, Jun 9, 2011 at 3:03 PM, Sambuddho Chakravarty <sc2516 at columbia.edu
> > wrote:
>> Dear Roger
>>  Thanks for your response. I read the spec document about the RELAY_DROP
>> cells. You say that no one has understood the passive correlation attack to
>> utilize the RELAY_DROP cells. I am however little curious to see if
>> "moderate padding" (enough to not mess up QoS of various services) can be
>> used to prevent some of the attacks that rely on parameters such as OWD ,
>> RTT and B/W variation to link relays that are being used in a circuit. I am
>> curious from the practical point of view of exploring such padding to
>> prevent our bandwidth based confirmation attack or the M&D attack (and its
>> 2009 variant) .
>> Thanks
>> Sambuddho
>> On Thu, Jun 9, 2011 at 12:29 PM, Roger Dingledine <arma at mit.edu> wrote:
>>> On Wed, Jun 08, 2011 at 08:11:58PM -0400, Sambuddho Chakravarty wrote:
>>> > Hi All
>>> > I read in the Tor design spec that Tor control protocol supports
>>> keepalive
>>> > messages which could be used for link padding . I wonder if anyone has
>>> ever
>>> > explored using them...
>>> I don't think you mean the Tor control protocol. There's no need to pad
>>> that connection (or if there is, you've screwed up badly somewhere else).
>>> The Tor protocol supports PADDING cells -- see sec 3 of tor-spec.txt:
>>>   PADDING cells are currently used to implement connection keepalive.
>>>   If there is no other traffic, ORs and OPs send one another a PADDING
>>>   cell every few minutes.
>>> There's also a DROP relay cell. While PADDING cells can only be sent to
>>> the adjacent relay, the client can send DROP cells to any relay on her
>>> circuit, and any relay on the circuit can inject DROP cells to the
>>> client.
>>> See also sec 7.2 of tor-spec.
>>> But that said, I think the answer to your question is no. AFAIK nobody
>>> has understood passive correlation attacks well enough to get to the
>>> "if I change the design like this, does the attack work less well"
>>> research stage.
>>> --Roger
>>> _______________________________________________
>>> tor-dev mailing list
>>> tor-dev at lists.torproject.org
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