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

From: Jared Lee Richardson <jaredr26@gmail•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: Wed, 7 Jun 2017 14:43:14 -0700	[thread overview]
Message-ID: <CAD1TkXsrV3hmyEcpNXFdfWfTp3yLA4iKNCkp7FzjaATkXrmVnw@mail.gmail.com> (raw)
In-Reply-To: <CADvTj4pEGoMUN_fn1bywzhV-WkRP7sQ6fofXKsYJsYjq329b9g@mail.gmail.com>

> Keep in mind that this is only temporary until segwit has locked in,
after that happens it becomes optional for miners again.

I missed that, that does effectively address that concern.  It appears
that BIP148 implements the same rule as would be required to prevent a
later chainsplit as well, no?

This comment did bring to mind another concern about BIP148/91 though,
which I'll raise in the pull request discussion.  Feel free to respond
to it there.

Jared

On Wed, Jun 7, 2017 at 2:21 PM, James Hilliard
<james.hilliard1@gmail•com> wrote:
> Keep in mind that this is only temporary until segwit has locked in,
> after that happens it becomes optional for miners again.
>
> On Wed, Jun 7, 2017 at 4:09 PM, Jared Lee Richardson <jaredr26@gmail•com> wrote:
>>> 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.
>>
>> FYI, even if very successful, this deployment and change may have a
>> severe negative impact on a small group of miners.  Any miners/pools
>> who are not actively following the forums, news, or these discussions
>> may be difficult to reach and communicate with in time, particularly
>> with language barriers.  Of those, any who are also either not
>> signaling segwit currently or are running an older software version
>> will have their blocks continuously and constantly orphaned, but may
>> not have any alarms or notifications set up for such an unexpected
>> failure.  That may or may not be a worthy consideration, but it is
>> definitely brusque and a harsh price to pay.  Considering the
>> opposition mentioned against transaction limits for the rare cases
>> where a very large transaction has already been signed, it seems that
>> this would be worthy of consideration.  For the few miners in that
>> situation, it does turn segwit from an optional softfork into a
>> punishing hardfork.
>>
>> I don't think that's a sufficient reason alone to kill the idea, but
>> it should be a concern.
>>
>> Jared
>>
>> On Wed, Jun 7, 2017 at 7:10 AM, Erik Aronesty via bitcoin-dev
>> <bitcoin-dev@lists•linuxfoundation.org> wrote:
>>> 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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>>>
>>>
>>>
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