Date: Mon, 13 Aug 2018 20:32:33 +0000
To: Pieter Wuille <pieter.wuille@gmail.com>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Witness serialization in PSBT non-witness UTXOs
Precedence: list

Hi,

Since the BIP is already in proposed status, I think that we should specify=
 the non-witness utxo to just be "witness or non-witness" serialization. Th=
is maintains compatibility with things that have already implemented but al=
so 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 Me=
ssage =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@lis=
ts.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 could
>     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 lat=
e
>     for that, it should instead be updated to explicitly specify with or
>     witnout witness, but it's safe to drop the witness.
>
>     Opinions?
>
>     Cheers,
>
>     --
>     Pieter
>
>
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