Date: Fri, 06 Jul 2018 14:59:50 -0400
To: William Casarin <jb55@jb55.com>
From: Achow101 <achow101-lists@achow101.com>
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Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP 174 thoughts
Precedence: list

Hi,

=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 July 5, 2018 12:20 PM, William Casarin <jb55@jb55.com> wrote:

> =E2=80=8B=E2=80=8B
>=20
> I have another concern with the format. (my original bip comment for some=
 context: [1])
>=20
> It looks like the one of the reasons I was confused is because you can
>=20
> only parse the format properly by first deserializing the transaction.
>=20
> Since there is no "length" field for the key-value map arrays, you must
>=20
> count the number of transaction input/outputs, and use that as the
>=20
> number of kv maps to parse.

I don't think this is really a problem.

Almost all roles have to deserialize the unsigned tx anyways before they ca=
n do anything.
The only role that doesn't is a simple combiner (a combiner that does sanit=
y checks would
still have to deserialize the unsigned tx), and even then it doesn't matter=
. It just shoves
key value pairs together and doesn't need to know whether the map is for an=
 input or for
an output.

>=20
> This is pretty brittle, because now if a Combiner writes the wrong
>=20
> number of key-value maps that don't align with the number of inputs and
>=20
> outputs in the transaction, then the psbt will not be able to be
>=20
> deserialized properly, but is still a valid PSBT. It can't even detect
>=20
> these situations, because the input and output types share the same enum
>=20
> values.=20

If a combiner writes the wrong number of key-value maps, then it would simp=
ly be invalid
to the next person that receives the PSBT. It would not deserialize properl=
y because the
key value pairs would have incorrect values for their types. Not deserializ=
ing properly means
that the PSBT is simply invalid. The same numerical types might
be shared, but their meanings are different between the input and output ty=
pes.

I don't see anywhere that says the number of key value maps MUST
>=20
> match the number of inputs/outputs, perhaps it's implied?

I have added that to the BIP.

=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 July 5, 2018 10:23 AM, Jason Les <jasonles@gmail.com> wrote:

> Has there been any thought to standardizing file names used when creating=
 .psbt files? Maybe something that gives some reliability of being collisio=
n resistant and descriptive. For example:
>=20
> [8 char trim of hash of unsigned tx]+[Role that created file (Ex: Signer)=
]+[4 char trim of hash of data unique to that role (Ex: partial sig)]
>=20
> It may be useful to especially the combiner to have some idea of what fil=
es they have.
>=20
> -Jason Les

I haven't considered this, but I'm not sure if it is really useful. I don't=
 think it is really necessary
for any role to know who created the PSBT. If it did, this information woul=
d generally come
out-of-band anyways as someone has to give the PSBT to that person.


Andrew