On Tue, Jun 19, 2018 at 05:20:34PM +0200, Jonas Schnelli wrote:
...
> 
> I don’t see any reasons why space would be an issue.
> 
> HWWs probably can’t handle PBST natively since it is not optimised for
> presenting various informations in a signing-verification.

The Coldcard hardware wallet is PSBT native and does work directly from PSBT.

> A single stream-in of a PSBT through USB (or similar channel) will not work in
> many cases since HWW come often with very restrictive RAM constraints.

For the Coldcard, we expect a PSBT to be 'uploaded' over USB (can
also be provided on MicroSD card) and we work in-place with it,
scanning over it a few different times. If the user approves the
transaction, we produce a signed PSBT or final transaction and that
gets downloaded.

We support 256k byte PSBT files with hundreds of inputs/outputs
(IIRC, and exact limits still TBD) and are operating in a system
with only 25k free RAM after startup.

> Furthermore, I forget to mention in my last mail, that registering (or defining)
> a mime-type for PSBT would probably a great usability feature.
> (Send PSBT by email/messanger and with dbl-click to open feature, etc.)

+1 for mimetype, especially since it's a binary format.

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Peter D. Gray  ||  Founder, Coinkite  ||  Twitter: @dochex  ||  GPG: A3A31BAD 5A2A5B10