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 > 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 > 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 >> > 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. >> >> 
>> BIP: splitprotection
>> Layer: Consensus (soft fork)
>> Title: User Activated Soft Fork Split Protection
>> Author: James Hilliard >
>> Comments-Summary: No comments yet.
>> Comments-URI:
>> Status: Draft
>> Type: Standards Track
>> Created: 2017-05-22
>> License: BSD-3-Clause
>>          CC0-1.0
>>
>> >> ==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 === >> >> 
>> // 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");
>>   }
>> }
>>
>> >> 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 >> >>