Hi all,

While implementing PSBT support in the *btclib* library (
https://github.com/btclib-org/btclib), I have failed to understand the
rationale for the *proprietary* and *proof-of-reserves* types.

First off, at face value they have nothing to do with the operations
intrinsically required to finalize a valid transaction from PSBT
manipulation.

Moreover, whatever information content they can provide for non-standard
PSBT manipulation, that content could stay in the *unknown* field without
any loss of generality. How to structure and deal with unknown data would
be the responsibility of proprietary software or users wanting to provide
proof-of-reserve. As long as BIP174 clearly prescribes that unknown data
must be kept during PSBT manipulation, that should be enough.

Let me stress the above point: I have a project where we include
proprietary information in the PSBT. Any PSBT software supporting unknown
data gently keeps our proprietary information and our proprietary software
retrieves that data from serialized PSBT with no problem. There is no need
for a PSBT implementation to provide explicit support for *proprietary* and
*proof-of-reserves* types.

My last conclusion is reinforced by the evidence of all PSBT
implementations I know of, including bitcoin core and HWI, not implementing
proprietary and proof-of-reserve types. There is a high probability that
part of BIP174 would be just ignored.

Am I missing something?

Thanks
--
*Ferdinando M. Ametrano*
www.ametrano.net/about