[mosh-devel] thoughts on mosh

[Hari Balakrishnan]

If you have root access, which may be a good assumption for ToR (?), then one can run SSP over raw-IP packets made to look exactly like TCP packets...

Hari

PS: Hi Roger.

On May 15, 2012, at 4:00 PM, Keith Winstein wrote:

> FYI
> 
> 
> ---------- Forwarded message ----------
> From: Jacob Appelbaum <jacob at appelbaum.net>
> Date: Tue, May 15, 2012 at 9:55 AM
> Subject: thoughts on mosh
> To: harig at mit.edu, keithw at mit.edu
> Cc: Roger Dingledine <arma at mit.edu>
> 
> 
> Hi guys,
> 
> I'm some guy who found your project, mosh, and I was really happy to
> find a great example of how to make a project. I think I'll use it as an
> example of inventing something awesome, punting to other tools that do
> specific jobs you're not interested in solving, and generally doing a
> great job at encouraging peer review. I especially enjoy your mockery of
> startup culture while actually being a shining example of Free Software!
> I rather enjoyed the mosh paper as well.
> 
> I have a few thoughts about mosh - they mostly come from my interest as
> a Tor developer ( https://www.torproject.org/ ) but I also just wanted
> to say thanks for your smart work.
> 
> First up - I was really happy with how easy mosh is to setup - I was
> able to get started in less than five minutes on two different platforms
> after reading half a man page. That's pretty great!
> 
> I was a bit surprised by a few things - the first is that mosh binds to
> a range of high ports, I'd like it if by default it tries to bind to
> 5353, 53, 0 or even an ICMP socket; there's a good chance that those
> first two ports won't be blocked, the third requires some hacking and
> the fourth obviously requires some caps. I think it should be possible
> to get the caps required without being setuid but it's obviously a
> violation of your 'no special privileges' rule of thumb.
> 
> I have set my mosh client to request port 5353 (mdns) and I've found
> that even on networks that tamper with DNS (transparent proxies), they
> don't seem to tamper with (!) mosh traffic.
> 
> The second thing that surprised me was that mosh doesn't actually
> provide total confidentiality. In some very basic packet captures on my
> own laptop traffic, I saw a lot of zeros and some incrementing fields.
> If nothing else, I was surprised that this allows for trivial traffic
> analysis - watching a single server would allow you to correlate all of
> a given user's sessions across time and locations. I might be wrong
> about that but I suspect that is correct as the plaintext is all, well,
> plaintext. :(
> 
> I suspect that this is going to cause mosh to be trivially filtered in
> places like China or Iran, places where I very much expect to use mosh
> because of latency issues.
> 
> What do you think about actually providing confidentiality for
> everything? The packet lengths are already variable and the setup can
> happen indirectly, so once a session is up - the rest of the protocol
> could be a lot harder to classify, if you want... I'd sure like it!
> 
> The third thing is that mosh is basically the perfect thing for Tor
> users with one tiny exception: UDP (!)
> 
> Tor is for TCP connections and so UDP traffic will just leak or be
> dropped entirely - it depends on how the user configures things. I
> generally SSH to a given host and then attach to a screen session. Gah,
> if you thought SSH was slow directly, ha! It's not really very usable,
> as you can imagine. The trade off is location privacy and that is worth
> the cost in a lot of cases. If I had a single feature request, I'd be
> able to ssh over Tor, setup a mosh session and then have the remote mosh
> listener open a TCP receiver on the other end - this would allow me to
> Torify the mosh client entirely - something that would make my ssh + Tor
> + screen + irssi + mutt + bash experience really usable.
> 
> What do you think of that? Is that something that might be possible as
> an addition in the future? I understand from the paper that REX is close
> to what I'd like but _only_ for the TCP transport. mosh is clearly
> better in every single way - from ease of setup to ease of use for the
> _other_ things I'd like to do, such as using my terminal!
> 
> Sadly the lack of a TCP fall-back or proxy-able operation and the
> exposure of session information is something that would be worth
> discussing, I think. I feel like Tor is the perfect "worst case" network
> to try to work over...
> 
> I've also cc'ed Roger, the creator of Tor as I bet he'd love to see Tor
> and mosh work together; I bet he'll have something interesting to say too.
> 
> All the best,
> Jacob