From: Rusty Russell <rusty@rustcorp.com.au>
To: Russell O'Connor <roconnor@blockstream.io>, Luke Dashjr <luke@dashjr.org>
In-Reply-To: <CAMZUoKnjc4ezVm4FeMFA-+=g13E5ZwZCAoAjd_yL89v7qf1gEA@mail.gmail.com>
References: <201705121922.57445.luke@dashjr.org>
	<CAMZUoKnzV9faJ+mBTTzTre05Ejwnx3tC4ozbiPoPUfS+7GLMTQ@mail.gmail.com>
	<201705130526.59467.luke@dashjr.org>
	<CAMZUoKnjc4ezVm4FeMFA-+=g13E5ZwZCAoAjd_yL89v7qf1gEA@mail.gmail.com>
Date: Mon, 15 May 2017 10:44:13 +0930
Message-ID: <87tw4mly56.fsf@rustcorp.com.au>
MIME-Version: 1.0
Content-Type: text/plain
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] BIP: Block signal enforcement via tx fees
Precedence: list

Russell O'Connor via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
writes:
> On Sat, May 13, 2017 at 1:26 AM, Luke Dashjr <luke@dashjr.org> wrote:
>
>> Versionbits change/lose their meaning after the deployment timeout. For
>> this
>> reason, the timeout must be specified so the check is skipped when that
>> occurs.
>>
>
> To add a timeout a user can optionally bundle a pair of similar
> transactions.  One with the transaction version bits set and a second with
> a locktime set.  The effect is the same.

I have a similar proposal to Russell; use tx nVersion.  However, my
subset is simpler, and uses fewer precious nVersion bits:

1. Top version 26 bits must be 1 (say)
2. Next bit indicates positive (must have bit set) or negative (must NOT
   have bit set).
3. Bottom 5 bits refer to which BIP8/9 bit we're talking about.

This only allows specifying a single bit, and only support BIP8/9-style
signalling.

I believe we can skip the timeout: miners don't signal 100% either way
anyway.  If a BIP is in LOCKIN, wallets shouldn't set positive on that
bit (this gives them two weeks).  Similarly, if a BIP is close to
FAILED, don't set positive on your tx.  Wallets shouldn't signal until
any bit until see some minimal chance it's accepted (eg. 1 in 20 blocks).

> I recall chatting about this idea recently and my conclusion was the same
> as Peter Todd's conclusion: this will just encourage miners to false signal
> readiness with undermines both BIP 9 and BIP 8.

This is gentler on miners than a UASF flag day, and does offer some
harder-to-game signalling from bitcoin users.

False signalling miners still have the 2 week LOCKIN period to upgrade,
otherwise they can already lose money.  You could argue they're *more*
likely to upgrade with a signal that significant parts of the economy
have done so.

Cheers,
Rusty.