You need a majority of miners enforcing BIP148 upon BIP148 activation to prevent a split, not just a majority signalling segwit. This provides a miner coordination mechanism for BIP148 mandatory signalling enforcement.
On Tue, Jun 6, 2017 at 8:11 PM, Karl Johan Alm <karljohan-...@garage.co.jp> wrote: > One thing about BIP148 activation that may be affected by this is the > fact that segwit signalling non-BIP148 miners + BIP148 miners may hold > majority hash power and prevent a chain split. With this SF, that will > no longer be the case, right? Or am I completely confused on the > subject? > > On Wed, Jun 7, 2017 at 9:56 AM, 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.hillia...@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 _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
