MIME-Version: 1.0
From: Jacob Eliosoff <jacob.eliosoff@gmail.com>
Date: Fri, 9 Jun 2017 00:40:57 -0400
Message-ID: <CAAUaCygRaXNX5xWuka1xrrXwKv1tqevT9-cHd-5mh_AkHpg9gA@mail.gmail.com>
To: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary="001a11401bc4559d1305517f9300"
Subject: [bitcoin-dev] The BIP148 chain split may be inevitable
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I've been trying to work out the expected interaction between James
Hilliard's BIP91 [1] (or splitprotection [2], or Segwit2x [3], which both
use variants of BIP91 activation) and the BIP148 UASF [4].  Some of this is
subtle so CORRECTIONS WELCOME, but my conclusions are:
1. It's extremely unlikely BIP91-type logic can activate segwit in time to
avoid a BIP148 chain split.
2. So, in practice all we can do is ensure the BIP148 split is as painless
as possible.

REASONING:  First, some dates.  BIP148, whose deadline is already deployed
and thus unlikely to be postponed, starts orphaning non-segwit blocks on
midnight (GMT) the morning of August 1.  Meanwhile, here are Bitcoin's
rough expected next four difficulty adjustment dates (they could vary by
~1-3 days depending on block times, but it's unlikely to matter here):
1. June 17
2. June 30
3. July 13
4. July 27

If Segwit activates on adj date #5 or later (August), it will be too late
to avoid BIP148's split, which will have occurred the moment August began.
So, working backwards, and assuming we want compatibility with old BIP141
nodes:

- Segwit MUST activate by adj #4 (~July 27)
- Therefore segwit MUST be locked in by adj #3 (~July 13: this is
inflexible, since this logic is in already-deployed BIP141 nodes)
- Therefore, I *think* >50% of hashpower needs to be BIP91 miners,
signaling bit 1 and orphaning non-BIP91 (ie, BIP91's bit 4 must activate),
by adj #2 (June 30)?
- Therefore, as currently designed, BIP91 bit 4 must be locked in by adj #1
(June 17)
- Therefore, >=80% of hashrate must start signaling BIP91's bit 4 by a few
days ago...

There are ways parts of this could be sped up, eg, James' "rolling
100-block lock-in periods" [5], to get BIP91 signaling bit 1 sooner.  But
to be compatible with old BIP141 nodes, >50% of hashrate must be activated
BIP91 miners by ~June 30: there's no fudging that.

So, it seems to me that to avoid the BIP148 split, one of two things would
have to happen:
a) 95% of hashrate start signaling bit 1 by ~June 30.  Given current stat
is 32%, this would basically require magic.
b) BIP91 is deployed and >50% (80% or whatever) of hashrate is *activated*
BIP91 miners by ~June 30, ~3 weeks from now.  Again, much too soon.

So, I think the BIP148 split is inevitable.  I actually expect that few
parts of the ecosystem will join the fork, so disruption will be bearable.
But anyway let me know any flaws in the reasoning above.

[1] https://github.com/bitcoin/bips/blob/master/bip-0091.mediawiki
[2]
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-June/014508.html
[3] https://github.com/btc1/bitcoin/pull/11
[4] https://github.com/bitcoin/bips/blob/master/bip-0148.mediawiki
[5] https://github.com/btc1/bitcoin/pull/6#issuecomment-305917729

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<div dir=3D"ltr"><div>I&#39;ve been trying to work out the expected interac=
tion between James Hilliard&#39;s BIP91 [1] (or splitprotection [2], or Seg=
wit2x [3], which both use variants of BIP91 activation) and the BIP148 UASF=
 [4].=C2=A0 Some of this is subtle so CORRECTIONS WELCOME, but my conclusio=
ns are:</div><div>1. It&#39;s extremely unlikely BIP91-type logic can activ=
ate segwit in time to avoid a BIP148 chain split.</div><div>2. So, in pract=
ice all we can do is ensure the BIP148 split is as painless as possible.</d=
iv><div><br></div><div>REASONING: =C2=A0First, some dates.=C2=A0 BIP148, wh=
ose deadline is already deployed and thus unlikely to be postponed, starts =
orphaning non-segwit blocks on midnight (GMT) the morning of August 1.=C2=
=A0 Meanwhile, here are Bitcoin&#39;s rough expected next four difficulty a=
djustment dates (they could vary by ~1-3 days depending on block times, but=
 it&#39;s unlikely to matter here):</div><div>1. June 17</div><div>2. June =
30</div><div>3. July 13</div><div>4. July 27</div><div><br></div><div>If Se=
gwit activates on adj date #5 or later (August), it will be too late to avo=
id BIP148&#39;s split, which will have occurred the moment August began.=C2=
=A0 So, working backwards, and assuming we want compatibility with old BIP1=
41 nodes:</div><div><br></div><div>- Segwit MUST activate by adj #4 (~July =
27)</div><div>- Therefore segwit MUST be locked in by adj #3 (~July 13: thi=
s is inflexible, since this logic is in already-deployed BIP141 nodes)</div=
><div>- Therefore, I *think* &gt;50% of hashpower needs to be BIP91 miners,=
 signaling bit 1 and orphaning non-BIP91 (ie, BIP91&#39;s bit 4 must activa=
te), by adj #2 (June 30)?</div><div>- Therefore, as currently designed, BIP=
91 bit 4 must be locked in by adj #1 (June 17)</div><div>- Therefore, &gt;=
=3D80% of hashrate must start signaling BIP91&#39;s bit 4 by a few days ago=
...</div><div><br></div><div>There are ways parts of this could be sped up,=
 eg, James&#39; &quot;rolling 100-block lock-in periods&quot; [5], to get B=
IP91 signaling bit 1 sooner.=C2=A0 But to be compatible with old BIP141 nod=
es, &gt;50% of hashrate must be activated BIP91 miners by ~June 30: there&#=
39;s no fudging that.</div><div><br></div><div>So, it seems to me that to a=
void the BIP148 split, one of two things would have to happen:</div><div>a)=
 95% of hashrate start signaling bit 1 by ~June 30.=C2=A0 Given current sta=
t is 32%, this would basically require magic.</div><div>b) BIP91 is deploye=
d and &gt;50% (80% or whatever) of hashrate is *activated* BIP91 miners by =
~June 30, ~3 weeks from now.=C2=A0 Again, much too soon.</div><div><br></di=
v><div>So, I think the BIP148 split is inevitable.=C2=A0 I actually expect =
that few parts of the ecosystem will join the fork, so disruption will be b=
earable.=C2=A0 But anyway let me know any flaws in the reasoning above.</di=
v><div><br></div><div>[1] <a href=3D"https://github.com/bitcoin/bips/blob/m=
aster/bip-0091.mediawiki">https://github.com/bitcoin/bips/blob/master/bip-0=
091.mediawiki</a></div><div>[2] <a href=3D"https://lists.linuxfoundation.or=
g/pipermail/bitcoin-dev/2017-June/014508.html">https://lists.linuxfoundatio=
n.org/pipermail/bitcoin-dev/2017-June/014508.html</a></div><div>[3] <a href=
=3D"https://github.com/btc1/bitcoin/pull/11">https://github.com/btc1/bitcoi=
n/pull/11</a></div><div>[4] <a href=3D"https://github.com/bitcoin/bips/blob=
/master/bip-0148.mediawiki">https://github.com/bitcoin/bips/blob/master/bip=
-0148.mediawiki</a></div><div>[5] <a href=3D"https://github.com/btc1/bitcoi=
n/pull/6#issuecomment-305917729">https://github.com/btc1/bitcoin/pull/6#iss=
uecomment-305917729</a></div></div>

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