Packet Timing and Data Leaks

[Damien Miller]

On Thu, 3 Aug 2023, Chris Rapier wrote:

> Howdy all,
> 
> So, one night over beers I was telling a friend how you could use the timing
> between key presses on a type writer to extract information. Basically, you
> make some assumptions about the person typing (touch typing at so many words
> per second and then fuzzing the parameters until words come out).
> 
> The I found a paper written back in 2001 talked about using the interpacket
> timing in interactive sessions to leak information.
> https://people.eecs.berkeley.edu/~dawnsong/papers/ssh-timing.pdf
> 
> I'm sure this has been addressed (or dismissed) but I'm looking for the
> specific section of code that might deal with this. Any pointers?

The main issue raised in that paper was that it was trivially detectable
when terminal echo was switched off and so an attacker could specifically
observe the moments when users were typing their passwords into (say)
sudo. This got fixed around the time the paper was released IIRC,
search for "Simulate echo" in channels.c:channel_handle_wfd().

The broader issue of hiding all potential keystroke timing is not yet fixed.

-d