Subject: Re: [Bitcoin-development] Payment Protocol for Face-to-face Payments

From: Adam Back <[email-masked]>
Date: Thu, 20 Mar 2014 13:12:21 +0100

Whats a sensible limit on practical/convenient QR code size?

How much of the payment protocol message size comes from use of x509?

(Just exploring what the options are).

Adam

On Thu, Mar 20, 2014 at 11:36:09AM +0100, Mike Hearn wrote:
>   Encoding entire payment requests into qrcodes is definitely not the way
>   to go. They can already be large when signed and we're just at the
>   start of adding features.
>   Finishing off and standardising the bluetooth support is the way to go
>   (r=bt:mac). Andreas' app already has some support for this I believe,
>   so Alex you could prototype with that, but we need to:
>   1) Add an encryption/auth layer on top, because it runs over RFCOMM
>   sockets. The authentication would require proof of owning the Bitcoin
>   key that's in the address part of the URI (which is needed for
>   backwards compat anyway).
>   2) Write a BIP for it and make sure it's interoperable
>   For the auth layer we could either use SSL and then just ignore the
>   server certificate and require signing of the session public key with
>   the Bitcoin key, which should be easy to code up but is rather heavy on
>   the air, or roll a custom lightweight thing where we just do a basic
>   ECDH, with the servers key being the same as the address key. But
>   rolling such protocols is subtle and I guess it'd need to be reviewed
>   by people familiar with such things.
>   This feels like a good opportunity to grow the community - perhaps we
>   can find a volunteer in the forums who enjoys crypto.