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Date: Wed, 16 Nov 2016 16:01:00 -0500
From: Peter Todd <pete@petertodd.org>
To: Alex Morcos <morcos@gmail.com>,
Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Message-ID: <20161116210100.GC5639@savin.petertodd.org>
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Subject: Re: [bitcoin-dev] [BIP Proposal] Buried Deployments
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On Wed, Nov 16, 2016 at 09:32:24AM -0500, Alex Morcos via bitcoin-dev wrote:
> I think we are misunderstanding the effect of this change.
> It's still "OK" for a 50k re-org to happen.
> We're just saying that if it does, we will now have potentially introduced
> a hard fork between new client and old clients if the reorg contains
> earlier signaling for the most recent ISM soft fork and then blocks which
> do not conform to that soft fork before the block height encoded activati=
on.
>=20
> I think the argument is this doesn't substantially add to the confusion or
> usability of the system as its likely that old software won't even handle
> 50k block reorgs cleanly anyway and there will clearly have to be human
> coordination at the time of the event. In the unlikely event that the new
> chain does cause such a hard fork, that coordination can result in everyo=
ne
> upgrading to software that supports the new rules anyway.
>=20
> So no, I don't think we should add a checkpoint. I think we should all
> just agree to a hard fork that only has a very very slim chance of any
> practical effect.
So, conceptually, another way to deal with this is to hardcode a blockhash
where we allow blocks in a chain ending with that blockhash to _not_ follow
BIP65, up until that blockhash, and any blockchain without that blockhash m=
ust
respect BIP65 for all blocks in the chain.
This is a softfork: we've only added rules that made otherwise valid chains
invalid, and at the same time we are still accepting large reorgs (albeit u=
nder
stricter rules than before).
I'd suggest we call this a exemption hash - we've exempted a particular
blockchains from a soft-forked rule that we would otherwise enforce.
--=20
https://petertodd.org 'peter'[:-1]@petertodd.org
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