[tor-dev] Guard nodes and network down events
tom at ritter.vg
Thu Aug 14 13:18:03 UTC 2014
On 13 August 2014 07:47, George Kadianakis <desnacked at riseup.net> wrote:
> The fundamental issue here is that Tor does not have a primitive that
> detects whether the network is up or down, since any such primitive
> stands out to a network attacker .
I'm not certain this is true. Windows and Mac OS detect whether or
not there is a Captive Portal/Internet connection. While one can
argue this is bad practice, piggybacking on a detection mechanism used
by default in widely deployed OS's seems like it would not stand out.
Windows has IsInternetConnected  which uses NCSI.
I know less about Mac, but there is SCNetowrkReachability .
Apparently the (undocumented) way that Apple uses to detect captive
portals is .
It's not very clean to emulate a request instead of using an API, if
it came down to it. But while it may seem dangerous to emulate a
request that can change in an OS patch... the reality of it is that as
long as you pay attention to the patches, you'd be able to deploy a
fix long before a non-negligible portion of people patched anyway.
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