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From: Johnson Lau <jl2012@xbt.hk>
In-Reply-To: <201606080729.24789.luke@dashjr.org>
Date: Wed, 8 Jun 2016 16:23:51 +0800
Message-Id: <D192E876-1A4F-4B06-86F6-54F1BDEC857D@xbt.hk>
References: <A7E9BC23-6860-4B31-9D4E-11F771A5E581@xbt.hk>
	<201606080729.24789.luke@dashjr.org>
To: Luke Dashjr <luke@dashjr.org>
Cc: bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP141 segwit consensus rule update: extension of
	witness program definition
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> On 8 Jun 2016, at 15:29, Luke Dashjr <luke@dashjr.org> wrote:
>=20
> On Wednesday, June 08, 2016 5:57:36 AM Johnson Lau via bitcoin-dev =
wrote:
>> Why not make it even bigger, e.g. 75 bytes?
>=20
> I don't see a sufficient answer to this question. Pieter explained why =
>75
> would be annoying, but 75 seems like it should be fine.
>=20
>> In any case, since scripts with a 1-byte push followed by a push of =
>40
>> bytes remain anyone-can-spend, we always have the option to redefine =
them
>> with a softfork.
>=20
> It's not that simple, since this is preventing use of the witness =
field for
> such scripts. With this limit in place, any such a softfork would =
suddenly
> require either two different witness commitments, or disabling the =
previous
> witness transaction format.
>=20
> Luke

This is exactly why I proposed to extend the definition. My initial =
proposal was extending it to 33 bytes to effectively allow 16*256 new =
script versions, assuming we will keep using 32 bytes program hash.

If someday 32 bytes hash is deemed to be unsafe, the txid would also be =
unsafe and a hard fork might be needed. Therefore, I don=E2=80=99t see =
how a witness program larger than 40 bytes would be useful in any case =
(as it is more expensive and takes more UTXO space). I think Pieter =
doesn=E2=80=99t want to make it unnecessarily lenient.

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