Re: [bitcoin-dev] User Activated Soft Fork Split Protection

[Erik Aronesty <erik@q32.com>]

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This is, by far, the safest way for miners to quickly defend against a
chain split, much better than a -bip148 option.   This allows miners to
defend themselves, with very little risk, since the defense is only
activated if the majority of miners do so. I would move for a very rapid
deployment.   Only miners would need to upgrade.   Regular users would not
have to concern themselves with this release.

On Wed, Jun 7, 2017 at 6:13 AM, James Hilliard via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> I think even 55% would probably work out fine simply due to incentive
> structures, once signalling is over 51% it's then clear to miners that
> non-signalling blocks will be orphaned and the rest will rapidly
> update to splitprotection/BIP148. The purpose of this BIP is to reduce
> chain split risk for BIP148 since it's looking like BIP148 is going to
> be run by a non-insignificant percentage of the economy at a minimum.
>
> On Wed, Jun 7, 2017 at 12:20 AM, Tao Effect <contact@taoeffect.com> wrote:
> > See thread on replay attacks for why activating regardless of threshold
> is a
> > bad idea [1].
> >
> > BIP91 OTOH seems perfectly reasonable. 80% instead of 95% makes it more
> > difficult for miners to hold together in opposition to Core. It gives
> Core
> > more leverage in negotiations.
> >
> > If they don't activate with 80%, Core can release another BIP to reduce
> it
> > to 75%.
> >
> > Each threshold reduction makes it both more likely to succeed, but also
> > increases the likelihood of harm to the ecosystem.
> >
> > Cheers,
> > Greg
> >
> > [1]
> > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/
> 2017-June/014497.html
> >
> > --
> > Please do not email me anything that you are not comfortable also sharing
> > with the NSA.
> >
> > On Jun 6, 2017, at 6:54 PM, James Hilliard <james.hilliard1@gmail.com>
> > wrote:
> >
> > This is a BIP8 style soft fork so mandatory signalling will be active
> > after Aug 1st regardless.
> >
> > On Tue, Jun 6, 2017 at 8:51 PM, Tao Effect <contact@taoeffect.com>
> wrote:
> >
> > What is the probability that a 65% threshold is too low and can allow a
> > "surprise miner attack", whereby miners are kept offline before the
> > deadline, and brought online immediately after, creating potential havoc?
> >
> > (Nit: "simple majority" usually refers to >50%, I think, might cause
> > confusion.)
> >
> > -Greg Slepak
> >
> > --
> > Please do not email me anything that you are not comfortable also sharing
> > with the NSA.
> >
> > On Jun 6, 2017, at 5:56 PM, James Hilliard via bitcoin-dev
> > <bitcoin-dev@lists.linuxfoundation.org> wrote:
> >
> > Due to the proposed calendar(https://segwit2x.github.io/) for the
> > SegWit2x agreement being too slow to activate SegWit mandatory
> > signalling ahead of BIP148 using BIP91 I would like to propose another
> > option that miners can use to prevent a chain split ahead of the Aug
> > 1st BIP148 activation date.
> >
> > The splitprotection soft fork is essentially BIP91 but using BIP8
> > instead of BIP9 with a lower activation threshold and immediate
> > mandatory signalling lock-in. This allows for a majority of miners to
> > activate mandatory SegWit signalling and prevent a potential chain
> > split ahead of BIP148 activation.
> >
> > This BIP allows for miners to respond to market forces quickly ahead
> > of BIP148 activation by signalling for splitprotection. Any miners
> > already running BIP148 should be encouraged to use splitprotection.
> >
> > <pre>
> > BIP: splitprotection
> > Layer: Consensus (soft fork)
> > Title: User Activated Soft Fork Split Protection
> > Author: James Hilliard <james.hilliard1@gmail.com>
> > Comments-Summary: No comments yet.
> > Comments-URI:
> > Status: Draft
> > Type: Standards Track
> > Created: 2017-05-22
> > License: BSD-3-Clause
> >          CC0-1.0
> > </pre>
> >
> > ==Abstract==
> >
> > This document specifies a coordination mechanism for a simple majority
> > of miners to prevent a chain split ahead of BIP148 activation.
> >
> > ==Definitions==
> >
> > "existing segwit deployment" refer to the BIP9 "segwit" deployment
> > using bit 1, between November 15th 2016 and November 15th 2017 to
> > activate BIP141, BIP143 and BIP147.
> >
> > ==Motivation==
> >
> > The biggest risk of BIP148 is an extended chain split, this BIP
> > provides a way for a simple majority of miners to eliminate that risk.
> >
> > This BIP provides a way for a simple majority of miners to coordinate
> > activation of the existing segwit deployment with less than 95%
> > hashpower before BIP148 activation. Due to time constraints unless
> > immediately deployed BIP91 will likely not be able to enforce
> > mandatory signalling of segwit before the Aug 1st activation of
> > BIP148. This BIP provides a method for rapid miner activation of
> > SegWit mandatory signalling ahead of the BIP148 activation date. Since
> > the primary goal of this BIP is to reduce the chance of an extended
> > chain split as much as possible we activate using a simple miner
> > majority of 65% over a 504 block interval rather than a higher
> > percentage. This BIP also allows miners to signal their intention to
> > run BIP148 in order to prevent a chain split.
> >
> > ==Specification==
> >
> > While this BIP is active, all blocks must set the nVersion header top
> > 3 bits to 001 together with bit field (1<<1) (according to the
> > existing segwit deployment). Blocks that do not signal as required
> > will be rejected.
> >
> > ==Deployment==
> >
> > This BIP will be deployed by "version bits" with a 65%(this can be
> > adjusted if desired) activation threshold BIP9 with the name
> > "splitprotecion" and using bit 2.
> >
> > This BIP starts immediately and is a BIP8 style soft fork since
> > mandatory signalling will start on midnight August 1st 2017 (epoch
> > time 1501545600) regardless of whether or not this BIP has reached its
> > own signalling threshold. This BIP will cease to be active when segwit
> > is locked-in.
> >
> > === Reference implementation ===
> >
> > <pre>
> > // Check if Segregated Witness is Locked In
> > bool IsWitnessLockedIn(const CBlockIndex* pindexPrev, const
> > Consensus::Params& params)
> > {
> >   LOCK(cs_main);
> >   return (VersionBitsState(pindexPrev, params,
> > Consensus::DEPLOYMENT_SEGWIT, versionbitscache) ==
> > THRESHOLD_LOCKED_IN);
> > }
> >
> > // SPLITPROTECTION mandatory segwit signalling.
> > if ( VersionBitsState(pindex->pprev, chainparams.GetConsensus(),
> > Consensus::DEPLOYMENT_SPLITPROTECTION, versionbitscache) ==
> > THRESHOLD_LOCKED_IN &&
> >    !IsWitnessLockedIn(pindex->pprev, chainparams.GetConsensus()) &&
> > // Segwit is not locked in
> >    !IsWitnessEnabled(pindex->pprev, chainparams.GetConsensus()) ) //
> > and is not active.
> > {
> >   bool fVersionBits = (pindex->nVersion & VERSIONBITS_TOP_MASK) ==
> > VERSIONBITS_TOP_BITS;
> >   bool fSegbit = (pindex->nVersion &
> > VersionBitsMask(chainparams.GetConsensus(),
> > Consensus::DEPLOYMENT_SEGWIT)) != 0;
> >   if (!(fVersionBits && fSegbit)) {
> >       return state.DoS(0, error("ConnectBlock(): relayed block must
> > signal for segwit, please upgrade"), REJECT_INVALID, "bad-no-segwit");
> >   }
> > }
> >
> > // BIP148 mandatory segwit signalling.
> > int64_t nMedianTimePast = pindex->GetMedianTimePast();
> > if ( (nMedianTimePast >= 1501545600) &&  // Tue 01 Aug 2017 00:00:00 UTC
> >    (nMedianTimePast <= 1510704000) &&  // Wed 15 Nov 2017 00:00:00 UTC
> >    (!IsWitnessLockedIn(pindex->pprev, chainparams.GetConsensus()) &&
> > // Segwit is not locked in
> >     !IsWitnessEnabled(pindex->pprev, chainparams.GetConsensus())) )
> > // and is not active.
> > {
> >   bool fVersionBits = (pindex->nVersion & VERSIONBITS_TOP_MASK) ==
> > VERSIONBITS_TOP_BITS;
> >   bool fSegbit = (pindex->nVersion &
> > VersionBitsMask(chainparams.GetConsensus(),
> > Consensus::DEPLOYMENT_SEGWIT)) != 0;
> >   if (!(fVersionBits && fSegbit)) {
> >       return state.DoS(0, error("ConnectBlock(): relayed block must
> > signal for segwit, please upgrade"), REJECT_INVALID, "bad-no-segwit");
> >   }
> > }
> > </pre>
> >
> > https://github.com/bitcoin/bitcoin/compare/0.14...
> jameshilliard:splitprotection-v0.14.1
> >
> > ==Backwards Compatibility==
> >
> > This deployment is compatible with the existing "segwit" bit 1
> > deployment scheduled between midnight November 15th, 2016 and midnight
> > November 15th, 2017. This deployment is also compatible with the
> > existing BIP148 deployment. This BIP is compatible with BIP91 only if
> > BIP91 activates before it and before BIP148. Miners will need to
> > upgrade their nodes to support splitprotection otherwise they may
> > build on top of an invalid block. While this bip is active users
> > should either upgrade to splitprotection or wait for additional
> > confirmations when accepting payments.
> >
> > ==Rationale==
> >
> > Historically we have used IsSuperMajority() to activate soft forks
> > such as BIP66 which has a mandatory signalling requirement for miners
> > once activated, this ensures that miners are aware of new rules being
> > enforced. This technique can be leveraged to lower the signalling
> > threshold of a soft fork while it is in the process of being deployed
> > in a backwards compatible way. We also use a BIP8 style timeout to
> > ensure that this BIP is compatible with BIP148 and that BIP148
> > compatible mandatory signalling activates regardless of miner
> > signalling levels.
> >
> > By orphaning non-signalling blocks during the BIP9 bit 1 "segwit"
> > deployment, this BIP can cause the existing "segwit" deployment to
> > activate without needing to release a new deployment. As we approach
> > BIP148 activation it may be desirable for a majority of miners to have
> > a method that will ensure that there is no chain split.
> >
> > ==References==
> >
> > *[https://lists.linuxfoundation.org/pipermail/
> bitcoin-dev/2017-March/013714.html
> > Mailing list discussion]
> > *[https://github.com/bitcoin/bitcoin/blob/v0.6.0/src/main.
> cpp#L1281-L1283
> > P2SH flag day activation]
> > *[[bip-0009.mediawiki|BIP9 Version bits with timeout and delay]]
> > *[[bip-0016.mediawiki|BIP16 Pay to Script Hash]]
> > *[[bip-0091.mediawiki|BIP91 Reduced threshold Segwit MASF]]
> > *[[bip-0141.mediawiki|BIP141 Segregated Witness (Consensus layer)]]
> > *[[bip-0143.mediawiki|BIP143 Transaction Signature Verification for
> > Version 0 Witness Program]]
> > *[[bip-0147.mediawiki|BIP147 Dealing with dummy stack element
> malleability]]
> > *[[bip-0148.mediawiki|BIP148 Mandatory activation of segwit deployment]]
> > *[[bip-0149.mediawiki|BIP149 Segregated Witness (second deployment)]]
> > *[https://bitcoincore.org/en/2016/01/26/segwit-benefits/ Segwit
> benefits]
> >
> > ==Copyright==
> >
> > This document is dual licensed as BSD 3-clause, and Creative Commons
> > CC0 1.0 Universal.
> > _______________________________________________
> > bitcoin-dev mailing list
> > bitcoin-dev@lists.linuxfoundation.org
> > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
> >
> >
> >
> _______________________________________________
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> bitcoin-dev@lists.linuxfoundation.org
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