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

From: Tao Effect <contact@taoeffect•com>
To: James Hilliard <james.hilliard1@gmail•com>
Cc: Bitcoin Dev <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] User Activated Soft Fork Split Protection
Date: Tue, 6 Jun 2017 22:20:52 -0700	[thread overview]
Message-ID: <0CDEF5A2-0BAF-46E4-8906-39D4724AF3F2@taoeffect.com> (raw)
In-Reply-To: <CADvTj4q+oOS=DKfpiNQ6PAbksQfa1gKNfokr2Zc6PNGWqLyL4A@mail.gmail.com>

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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 <https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-June/014497.html>

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> On Jun 6, 2017, at 6:54 PM, James Hilliard <james.hilliard1@gmail•com <mailto: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 <mailto: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 <mailto:bitcoin-dev@lists•linuxfoundation.org>> wrote:
>> 
>> Due to the proposed calendar(https://segwit2x.github.io/ <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 <mailto: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 <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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