Re: [bitcoin-dev] CHECKSEQUENCEVERIFY - We need more usecases to motivate the change

From: Alex Morcos <morcos@gmail•com>
To: Rusty Russell <rusty@rustcorp•com.au>
Cc: Bitcoin Dev <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] CHECKSEQUENCEVERIFY - We need more usecases to motivate the change
Date: Thu, 15 Oct 2015 09:47:33 -0400	[thread overview]
Message-ID: <CAPWm=eUR1fo4iVX=-J7mO34LvT6akRy5=Cxjn7j64PBn+A_oGQ@mail.gmail.com> (raw)
In-Reply-To: <87pp0okeip.fsf@rustcorp.com.au>

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Mark,

You seemed interested in changing BIP 68 to use 16 bits for sequence number
in both the block and time versions, making time based sequence numbers
have a resolution of 512 seconds.

I'm in favor of this approach because it leaves aside 14 bits for further
soft forks within the semantics of BIP 68.

It would be nice to know if you're planning this change, and perhaps people
can hold off on review until things are finalized.

I'd cast my "vote" against BIP 68 without this change, but am also open to
being convinced otherwise.

What are other peoples opinions on this?

On Thu, Oct 8, 2015 at 9:38 PM, Rusty Russell via bitcoin-dev <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> Peter Todd <pete@petertodd•org> writes:
> > On Tue, Oct 06, 2015 at 12:28:49PM +1030, Rusty Russell wrote:
> >> Peter Todd via bitcoin-dev <bitcoin-dev@lists•linuxfoundation.org>
> >> writes:
> >> > However I don't think we've done a good job showing why we need to
> >> > implement this feature via nSequence.
> >>
> >> It could be implemented in other ways, but nSequence is the neatest and
> >> most straightforward I've seen.
> >>
> >> - I'm not aware of any other (even vague) proposal for its use?
> Enlighten?
> >
> > There's three that immediately come to mind:
> >
> > Gregory Maxwell has proposed it as a way of discouraging miners from
> > reorging chains, by including some of the low-order bits of a previous
> > block header in nSequence.
> >
> > A few people have proposed implementing proof-of-stake blocksize voting
> > with nSequence.
>
> Excellent, thanks!  It's good to have such ideas as a compass.  PoS
> voting seems like it won't be a problem in 5 bits.
>
> The "prevbits" idea would want more bits; naively 64 would be good, but
> I think there are some tricks we can use to make 32 work OK.  We would
> have to then split between nLocktime (if available) and multiple
> nSequence fields, and it would weaken it for some txs.
>
> There is one easy solution: change the BIP wording from:
>
> -For transactions with an nVersion of 2 or greater,
> +For transactions with an nVersion of 2,
>
> And on every tx bump, we decide whether to keep this scheme (mempool
> would enforce it always).
>
> Cheers,
> Rusty.
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