On Thu, Mar 6, 2014 at 12:26 PM, Andreas Schildbach <andreas@schildbach.de> wrote:

I'm not sure if iso-dep is the way to go here. Afaik as soon as you pick
up the phone the connection breaks.

If the phone isn't willing to immediately authorise then it'd have to fall back to HTTPS or Bluetooth as normal.

Besides, how do you plan to risk-analyse the memo field?

I guess only the amount and destination are relevant for risk analysis.

It's already very short if you can do without Android Beam, e.g. on
Android 2.3.

I think IsoDep based protocols must bypass Beam - when I scan my e-passport there's no beam animation.

The most obvious optimization to speed up signature checking is to make
it lazy. The user can already inspect the payment while signatures are
being checked.

Well, for <400msec there can't be any user interaction. But checking signatures on the payment request and constructing and signing the inputs can all be done in parallel - you should be able to max out every core, at least for a brief moment.

Even the current ~10 second roundtrip is a huge improvement to the
status quo. I recently tried to buy a subway ticket and it took me 7
full minutes (just for the payment process)!

Then that subway kind of sucks ;) Have you been to London and used Oyster? I think the capital wouldn't work at all without the low latency Oyster cards. The tube would have stopped scaling some time ago.