[liberationtech] Open Whisper Systems' neat asynch FPS "pre-keying"

[Gregory Maxwell]

On Thu, Aug 22, 2013 at 11:03 AM, Joseph Lorenzo Hall <joe at cdt.org> wrote:
> TextSecure’s upcoming iOS client (and Android data channel client) uses
> a simple trick to provide asynchronous messaging while simultaneously
> providing forward secrecy.

I've seen people want PGP to do this before— have every encrypted and
signed message you send include a number of single use ephemeral reply
coupons, to be used instead of key agreement with a fixed key...

The primary argument against it is that if the receiver changes
systems the messages will be undecodable.  You can do things to
prevent this, like backing up your tokens, but that defeats PFS.