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From: Rusty Russell <rusty@rustcorp.com.au>
To: Andrew Chow <achow101-lists@achow101.com>,
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Date: Thu, 07 Jan 2021 09:56:25 +1030
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Subject: Re: [bitcoin-dev] New PSBT version proposal
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Hi Andrew et al,
Very excited to see this progress; thanks for doing all the
work! Sorry for the delayed feedback, I didn't get to this before the
break.
> Additionally, I would like to add a new global field:
> * PSBT_GLOBAL_UNDER_CONSTRUCTION =3D 0x05
> =C2=A0 * Key: empty
> =C2=A0 * Value: A single byte as a boolean. 0 for False, 1 for True. All=
=20
> other values ore prohibited. Must be omitted for PSBTv0, may be omitted=20
> in PSBTv2.
>
> PSBT_GLOBAL_UNDER_CONSTRUCTION is used to signal whether inputs and=20
> outputs can be added to the PSBT. This flag may be set to True when=20
> inputs and outputs are being updated, signed, and finalized. However=20
> care must be taken when there are existing signatures. If this field is=20
> omitted or set to False, no further inputs and outputs may be added to=20
> the PSBT.
I wonder if this can be flagged simply by omitting the (AFAICT
redundant) PSBT_GLOBAL_INPUT_COUNT and PSBT_GLOBAL_OUTPUT_COUNT? What
are the purposes of those fields?
For our uses, there would be no signatures at this stage; it's simply a
subdivision of the Creator role. This role would be terminated by
removing the under-construction marker. For this, it could be clear
that such an under-construction PSBT SHOULD NOT be signed.
Otherwise, if an explicit marker is required, I would omit the value and
simply use its existence to as a flag. Having two "false" values is
simply asking for trouble.
Thanks!
Rusty.
PS. Perhaps we should change the name to PBT (Partial Bitcoin
Transaction) now, since it's more than just signing...
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