Packet Timing and Data Leaks

[Damien Miller]

On Tue, 8 Aug 2023, Damien Miller wrote:

> On Mon, 7 Aug 2023, Chris Rapier wrote:
> 
> > > The broader issue of hiding all potential keystroke timing is not yet fixed.
> > 
> > Could some level of obfuscation come from enabling Nagle for interactive
> > sessions that has an associated TTY? Though that would be of limited
> > usefulness in low RTT environments. I don't like the idea of having a steady
> > drip of packets as that seems problematic both in terms of code complexity and
> > network usage. I also don't like the idea of imposing random jitter though
> > that might be easier to implement. However, without actual modeling I have no
> > idea if that would actually improve things.
> 
> Nagle is usually turned off because it causes annoying perceptions of
> non-deterministic latency.
> 
> For ssh, IMO sending interactive traffic on a fixed clock (e.g. every
> 2-4ms) instead of as soon as possible, and adding fake keystroke packets
> for some interval after the user stops generating traffic is the way to
> fix it. I've slowly been preparing for this by reworking the mainloop and
> associated timers.

Here's the beginning of an implementation of this. Far from complete,
but the timing quantisation part seems to work at least.

https://github.com/djmdjm/openssh-wip/pull/24

-d