> Can you elaborate what benefits you would get from the library approach
and how the library API would be different form the proposed URI-scheme?

The main benefit is that you don't need "standard" to solve problem, but use natural tools in given environment and programming stack. Build a "standard" on top of URI protocol is a huge limitation, which does not give any advantage.

We already see issues with dead simple "bitcoin uri" standard, it barely works in most of bitcoin apps. Think of vague definitions of parameters or ability to send payment requests over it. HW API would be complicated by an order of magnitude and I have serious concerns that it will be helpful for anything. So why complicate things.

> How would the library approach work on mobile platforms? Would USB be
the only supported hardware communication layer?

Interprocess communication/libraries/dependencies on Android are not bound to specific transport anyhow. Such library could be used by any android app, and the library would implement proper transports for various supported vendors. USB for Trezor, NFC for something different etc. If the point is "make life of app developers easier", let's do this and do not define artifical "standards".

slush

On Thu, Aug 18, 2016 at 8:54 AM, Jonas Schnelli <dev@jonasschnelli.ch> wrote:

Hi

> I fundamentally disagree with the concept of driving signing workflow by
> the wallet software. Wallet software does not know in advance all data
> necessary for the signer to do the job. As Jochen mentioned above,
> Segwit vs Non-segwit use cases are a good example, but there may be many.

I think this is easily solvable. The required data to verify and sign a
(standard) bitcoin transaction (including P2WSH multi-sig) is manageable.

IMO what a signing devices requires in order to sign a (standard)
transaction:
-> serialized tx
-> serialized tx of the inputs
-> scriptPubKey of the inputs
-> inputs redeem-Scripts
-> input amounts
-> position of the change output any maybe its keypath
-> cosigners pubkeys for inputs and changeaddress

This seems to be manageable for a 1 round communication?
Or do I miss something?

> Currently the TREZOR protocol works like device is a server and wallet
> is a client calling methods on it. It's like: "Sign this for me,
> please", "Ok, give me this information", "Here it is", "Now I need this
> another piece".... "There is the signature". Wallet does not know in
> advance what will go next, and it is for sake of simplicity. I'm quite
> happy with the protocol so far.

I think multiple rounds would still be possible with a clever design.
Although I could imaging that >95% of the users transaction would
require only a single "shot".

Whats the benefits of the multiple rounds communication? Would a single
round result in to many data transported?

Passing a 300kb chunk (assuming a large transaction) over a URI scheme
requires a couple of milliseconds on standard Smartphones or PCs.

> Considering the difference in between current hardware, I really don't
> think it is possible to find any minimal URI-based API good enough for
> communicating with all vendors. What I see more likely is some 3rd party
> libraries (JS, C++, Python, ...) defining high-level API and
> implementing hardware-specific protocols and transports as plugins. That
> way vendors are not limited by strict standard and application
> developers and services can integrate wide range of hardware wallets
> easily. However, this can be done already and we do not need any
> standardization process (yet).

The URI-based API allows transmitting data of multiple megabytes while
there is no need for...
* dependencies of any form (library, etc.)
* library support for a particular language
* platform that supports the dependencies of the library (like USBHID,
not supported by iOS)

Can you elaborate what benefits you would get from the library approach
and how the library API would be different form the proposed URI-scheme?

How would the library approach work on mobile platforms? Would USB be
the only supported hardware communication layer?

Thanks
--
</jonas>