Hey Pieter,
I think this is a reasonable collection of changes that make sense in
combination. Some initial feedback and questions.
>From the BIP:
> If one or more of the spending conditions consist of just a single key (after
> aggregation),
> he most likely one should be made the internal key
> > Even with this additions to the PSBT format, I think PSBT-signing
> > devices still need to store the xpubs of their co-signers. It's not
> > possible to safely show an incoming address to the user without a
> > full understanding of the other keys in a "multisig wallet". Also,
> > it represe
> I'd rather see the xpubs shared in the global section of the file,
> with the restriction that they must/should only include the hardened
> prefix of the path. The existing bip32 derivation path included in
> individual inputs and outputs be merged in as needed.
> After all in a typical PSBT, we
There are multiple references to "space savings", but no rationale for
treating "space" as something to save or even define. The costs are in CPU
time and I/O (which "space saving" doesn't necessarily reduce) and bandwidth
(which can often be reduced without "space saving" in commitments). The
