[OTR-dev] Persisting userstate object across app restarts.

[Nathan of Guardian]

On 08/12/2014 09:43 AM, Nathan of Guardian wrote:
> This isn't 100% the same but, our CacheWord library for Android does
> something along these lines - a dedicated service for just holding
> sensitive, unencrypted keys in memory:
> https://github.com/guardianproject/cacheword

Just to clarify, this library is meant for local, symmetric, non-PFS
keys (to unlock encrypted storage for instance), but the design of the
Android Service implementation is such that it is very minimal, and
meant to survive the OS's attempt to kill/destroy long-term background
services. This approach could be used to keep PFS keys in RAM. I believe
TextSecure uses a similar approach with their own code/service.

For those not used to mobile device app lifecycles, the idea that an
"app is running" doesn't really mean the same thing as on a desktop
system. If you have Pidgin with LibOTR running on your PC, it will stay
running until you exit the application, and its quite easy to keep OTR
sessions keys around as long as you need them. With Android however, and
to some extent iOS (though its different), apps have a much more
transient start/stop/pause/destroy state, and no foreground Activity or
background Service is guaranteed to stay running if the user is not
actively engaged with it. Even Services you mark as "Foreground" can
still be destroyed without warning on low RAM devices like the very
popular $100-200USD Moto G.

We've managed to make it work with ChatSecure, and I know TextSecure has
in their own way as well. Their pre-key work is the other solution to
the offline encrypted messaging, of course, but we haven't quite figured
out how to fit that into standard OTR yet.

+n