Date: Wed, 27 Jun 2018 09:39:02 -0400
To: William Casarin <jb55@jb55.com>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
From: Andrea <a.raspitzu@protonmail.com>
Reply-To: Andrea <a.raspitzu@protonmail.com>
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Subject: Re: [bitcoin-dev] BIP 174 thoughts
Precedence: list

Hi William, Andrew, list,

As noted by William there are some types missing in the global-types defini=
tion, because the number of each map for I/O must be known to the parser in=
 order to use the correct definitions for the types. At the moment a parser=
 reading a key-value record does not know whether it should read it as per-=
input type or per-output, a way to address this is to declare in advance th=
e number of maps and ensure they are ordered (inputs first). If you haven't=
 already worked out some types for that i propose using:

Number of inputs
- key (None, only the type): PSBT_GLOBAL_INPUT_NUMBER =3D 0x01 =20
- value: Varint=20

Number of outputs
- key (none, only the type): PSBT_GLOBAL_OUTPUT_NUMBER =3D 0x02
- value: Varint

On another note I think we can set a hard limit on the size of the PSBT, cu=
rrently is 'legal' to produce a very large PSBT with an excessive number of=
 Inputs and Outputs. By excessive I mean that even in the best case scenari=
o (using the smallest possible scriptPubKey as in P2WPKH) it is possible to=
 create a PSBT that would certainly create an invalid transaction (because =
of its size) when finalized. I haven't found anything related to this in th=
e previous discussions, please ignore this if it was already proposed/discu=
ssed.


Cheers, Andrea.

=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 June 27, 2018 8:09 AM, William Casarin via bitcoin-dev <bitcoin-dev@list=
s.linuxfoundation.org> wrote:

> =E2=80=8B=E2=80=8B
>=20
> Hey Andrew,
>=20
> If I'm reading the spec right: the way it is designed right now, you
>=20
> could create hundreds of thousands of zero bytes in the input or output
>=20
> key-value arrays. As far as I can tell this would be considered valid,
>=20
> as it is simply a large array of empty dictionaries. Is this right? I'm
>=20
> worried about buffer overflows in cases where someone sends a large blob
>=20
> of zeros to an unsuspecting implementation.
>=20
> Also, the extensibility section reads:
>=20
> > Additional key-value maps with different types for the key-value pairs
> >=20
> > can be added on to the end of the format.
>=20
> "different types for the key-value pairs", is this referring to new
>=20
> types beyond the current global, input and output types?
>=20
> > The number of each map that follows must be specified in the globals
> >=20
> > section
>=20
> Is this out of date? Since there is only one type in the global section
>=20
> now (tx).
>=20
> > so that parsers will know when to use different definitions of the
> >=20
> > data types
>=20
> I'm not sure what this means.
>=20
> Thanks!
>=20
> Will
>=20
>=20
> ------------------------------------------------
>=20
> https://jb55.com
>=20
> bitcoin-dev mailing list
>=20
> bitcoin-dev@lists.linuxfoundation.org
>=20
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev