[tor-dev] [Stegotorus] Fundamental problem with ack/retransmission mechanism

Jeroen Massar jeroen at massar.ch
Tue Jun 18 13:45:25 UTC 2013

On 2013-06-18 11:52 , Vmon wrote:
> Hey Zack,
> I'm not sure if you were following Iranian filtering few days leading to
> the election. It was basically http white-list. Psipohn was sending few 'GET
> / HTTP 1.1' before start sending any real data and it was able to fool
> the box . But the filtering is going to get more intelligent next time,
> and hence I feel stegotorus is more important than ever.

A little birdy whispered in my ear that a much revised version with a
lot of new features and various fixes including a lot of ack/retransmit
fixes should come available soon, but it is pending $org review... that
version even works fine on Windows btw.

> The fundamental thing that is not clear for me is that "If we have the
> assumption that TCP is reliable, this means all packets are going to
> arrive sooner or later. In such situation what's the need for
> re-transmission".

The problem is not about TCP, but more about HTTP where a censor or a
rate-limitter in general (eg Hotel WiFi tends to have issues) does not
always answer every HTTP request and thus one loses packets. Retransmit
is also important in those cases.


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