Packet Timing and Data Leaks

[Nico Kadel-Garcia]

On Thu, Aug 3, 2023 at 2:35 PM Chris Rapier <rapier at psc.edu> 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?
>
> Thanks,
>
> Chris

Why would any code "deal with this"? What you're describing is a form
of steganography, embedding another subtler, more dangerous message
inside the larger, safer, apparent message. Because there are so many
ways to hide such data, it's not even theoretically possible to avoid
altogether. OpenSSH would be the wrong layer of the stack to
manipulate this, especially given the attempts to improve interactive
behavior by improving responsiveness and reducing latency. If you're
making a system as swift and responsive as possible, it becomes very
difficult to regulate the timing of what may be human driven
interactions. And if you're going to manipulate packet delays.....
that's at the network layer or data layer, layer 2 or layer 3 of the
OSI stack. OpenSSH is more at the transport layer.

I don't see how OpenSSH could be written to avoid this.without
sacrificing responsive of interactive sessions.