On 23/09/13 07:12 AM, Dev Random wrote:
I've been thinking about this for a while now and I don't see a way to
do this with today's mobile devices without some external help.
The issue is that it's pretty much impossible to delete data securely
from a flash device.
Why is that?
That means that in order to guarantee PFS, you
have to store the keys in memory only. But again, in a mobile
environment, you don't have access to stable memory either, because of
the OS restarting your app, or the device itself rebooting.
Let's call this the persistence/deletion issue.
So, I submit that PFS in async messaging is impossible without help from
some kind of ephemeral, yet persistent storage. A possible solution
might be to store a portion of the key material (through Shamir's secret
sharing) on servers that you partially trust.
(I agree with the difficulty in general. Stating anything like PFS in
the context of a protocol makes less sense if one considers that the
clients either end save the messages.)
iang
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