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From: Gregory Maxwell <greg@xiph.org>
Date: Mon, 13 Aug 2018 20:39:38 +0000
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To: achow101-lists@achow101.com, 
	Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Witness serialization in PSBT non-witness UTXOs
Precedence: list

An alternative is to require reading either or but also require
writing without the witness.  It's likely that two years from now,
nothing will write the witnesses, and the requirement to support
reading them could be dropped.
On Mon, Aug 13, 2018 at 8:32 PM Achow101 via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
>
> Hi,
>
> Since the BIP is already in proposed status, I think that we should speci=
fy the non-witness utxo to just be "witness or non-witness" serialization. =
This maintains compatibility with things that have already implemented but =
also maintains the forwards compatibility that is needed.
>
> Andrew
>
>
> =E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90 Original =
Message =E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90
> On August 13, 2018 11:56 AM, Pieter Wuille via bitcoin-dev <bitcoin-dev@l=
ists.linuxfoundation.org> wrote:
>
> > Hello all,
> >
> > BIP174 currently specifies that non-witness UTXOs (the transactions
> > being spent by non-witness inputs) should be serialized in network
> > format.
> >
> > I believe there are two issues with this.
> >
> > 1.  Even in case the transaction whose output being spent itself has a
> >     witness, this witness is immaterial to PSBT. It's only there to be
> >     able to verify the txid commits to the output/amount being spent,
> >     which can be done without witness.
> >
> > 2.  "Network format" is a bit ambiguous. We can imagine a future
> >     softfork that introduces a new type of witness. Network format coul=
d
> >     be interpreted as including that new witness type, which is clearly
> >     unnecessary (by the above argument), and would gratuitously break
> >     compatibility with existing signers if implemented pedantically.
> >
> >     So my suggestion is to update the specification to state that
> >     non-witness UTXOs must be serialized without witness. If it's too l=
ate
> >     for that, it should instead be updated to explicitly specify with o=
r
> >     witnout witness, but it's safe to drop the witness.
> >
> >     Opinions?
> >
> >     Cheers,
> >
> >     --
> >     Pieter
> >
> >
> > bitcoin-dev mailing list
> > bitcoin-dev@lists.linuxfoundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>
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