[Cryptography] Rubber-hose resistance?

[Peter Gutmann]

[Multiple replies condensed into one]

Matt Palmer <matt at hezmatt.org> writes:

>On Wed, Dec 20, 2017 at 01:49:28AM +0000, Peter Gutmann wrote:
>>A password.  That's the one thing that's completely deniable (when it's used,
>>as in this case, to scp something over from some random server at some random
>>IP address).
>
>Do you take into account the possibility of MitM attacks post-border
>crossing, by making a record of the remote host key?  And if so, how?  

My threat model is twofold, principally that I'll have to explain to
organisations I'm under contract and/or NDA to that their sensitive data is
now in the hands of someone who didn't sign an NDA, and secondly that I'll be
detained by customs & immigration and/or have the laptop I need in order to
work seized.

If someone wants to carry out a concerted nation-state-level attack (utilising
border controls, post-border network MITMs, evil maids, and in general the
whole Mossad Doing Mossad Things) then I'll need a lot more security than scp.
For example an ORWL... which also means I may as well be wearing a t-shirt
with "US Customs, please detain this guy" printed on it.

The point is to travel with only the most standard, boring stuff, not anything
special that attracts attention.  You don't even need to have putty or scp
installed, just grab it from the Putty web site when you get there.  You're
trying to not attract attention so you can get to where you're going and get
on with work, not to fly with a suitcase full of James Bond gadgets.

Patrick <patrick at rayservers.net> writes:

>Use a strong 128-bit memorized password (e.g. from Diceware or using Ray
>Dillinger's technique) to ssh into the server.

You don't really need that, just something strong enough to stop scripts from
getting in.  Add fail2ban, long failed-password retry timeouts, and most
importantly something at a random port (not 22 or 443 or whatever) and you
should be OK.

Salt and pepper as required.  One trick I've used in the past is portrotate,
which changes the listening port every few minutes.  NTP sources are readily
accessible by standard tools, and won't look like suspicious activity.

Peter.