Re: [bitcoin-dev] Reduced signalling threshold activation of existing segwit deployment

From: Erik Aronesty <erik@q32•com>
To: Wang Chun <1240902@gmail•com>
Cc: Bitcoin Dev <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Reduced signalling threshold activation of existing segwit deployment
Date: Wed, 24 May 2017 12:44:55 -0400	[thread overview]
Message-ID: <CAJowKg+bD675iC9FUAP82KVUZteox9MGnd-EXqKr2tuQsCC5nA@mail.gmail.com> (raw)
In-Reply-To: <4C86CB4F-4ED2-4908-BF5D-6115891DA1D4@gmail.com>

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Yes, 75% seems fine - given that there is a already a wide deployment of
segwit enforcing nodes

This implementation is 100% compatible with a "UASF movement" since, if
triggered, it essentially turns all supporting miners into equivalent
BIP148 enforcers.   This should allay any fears that this would subvert a
UASF.

The proposed "agreement" which was reached without input from the
development community also apparently requires that a hard fork be locked
in on the same bit (bit 4).

Ideally, such a 2MB increase should be scheduled using BIP103-esqe logic:
Gradually increasing from 1MB to 2MB over the course of at least a couple
years, beginning 6 months from lock-in.

This will give developers ample time to evaluate and react to network
impacts.

On Wed, May 24, 2017 at 12:02 PM, Wang Chun via bitcoin-dev <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> I think we should go for 75%, same Litecoin. As I have said before, 95%
> threshold is too high even for unconventional soft forks.
>
> > 在 2017年5月24日，04:58，Andrew Chow via bitcoin-dev <bitcoin-dev@lists.
> linuxfoundation.org> 写道：
> >
> > Ah. I see now. It wasn't very clear to me that that is what will happen.
> >
> > Also, shouldn't the timeout date be set for before the BIP141 timeout?
> > Otherwise this could lock in but not have enough time for Segwit to be
> > locked in.
> >
> >
> >> On 5/23/2017 4:42 PM, James Hilliard wrote:
> >> That is incorrect, it is compatible with the current segwit
> >> implementation because it triggers a mandatory signalling period that
> >> will activate segwit on existing nodes.
> >>
> >> On Tue, May 23, 2017 at 4:39 PM, Andrew Chow via bitcoin-dev
> >> <bitcoin-dev@lists•linuxfoundation.org> wrote:
> >>> Hi James,
> >>>
> >>> From what I understand, this proposal is incompatible with the current
> >>> segwit implementation with regards to the NODE_WITNESS service bit. I
> >>> believe it could cause network partitioning if the service bit is not
> >>> changed.
> >>>
> >>> Andrew
> >>>
> >>>
> >>>> On 5/22/2017 6:40 PM, James Hilliard via bitcoin-dev wrote:
> >>>> I would like to propose an implementation that accomplishes the first
> >>>> part of the Barry Silbert proposal independently from the second:
> >>>>
> >>>> "Activate Segregated Witness at an 80% threshold, signaling at bit 4"
> >>>> in a way that
> >>>>
> >>>> The goal here is to minimize chain split risk and network disruption
> >>>> while maximizing backwards compatibility and still providing for rapid
> >>>> activation of segwit at the 80% threshold using bit 4.
> >>>>
> >>>> By activating segwit immediately and separately from any HF we can
> >>>> scale quickly without risking a rushed combined segwit+HF that would
> >>>> almost certainly cause widespread issues.
> >>>>
> >>>> Draft proposal:
> >>>> https://github.com/jameshilliard/bips/blob/bip-
> segsignal/bip-segsignal.mediawiki
> >>>>
> >>>> Proposal text:
> >>>> <pre>
> >>>>  BIP: segsignal
> >>>>  Layer: Consensus (soft fork)
> >>>>  Title: Reduced signalling threshold activation of existing segwit
> deployment
> >>>>  Author: James Hilliard <james.hilliard1@gmail•com>
> >>>>  Status: Draft
> >>>>  Type: Standards Track
> >>>>  Created: 2017-05-22
> >>>>  License: BSD-3-Clause
> >>>>           CC0-1.0
> >>>> </pre>
> >>>>
> >>>> ==Abstract==
> >>>>
> >>>> This document specifies a method to activate the existing BIP9 segwit
> >>>> deployment with a majority hashpower less than 95%.
> >>>>
> >>>> ==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==
> >>>>
> >>>> Segwit increases the blocksize, fixes transaction malleability, and
> >>>> makes scripting easier to upgrade as well as bringing many other
> >>>> [https://bitcoincore.org/en/2016/01/26/segwit-benefits/ benefits].
> >>>>
> >>>> This BIP provides a way for a simple majority of miners to coordinate
> >>>> activation of the existing segwit deployment with less than 95%
> >>>> hashpower. For a number of reasons a complete redeployment of segwit
> >>>> is difficulty to do until the existing deployment expires. This is due
> >>>> to 0.13.1+ having many segwit related features active already,
> >>>> including all the P2P components, the new network service flag, the
> >>>> witness-tx and block messages, compact blocks v2 and preferential
> >>>> peering. A redeployment of segwit will need to redefine all these
> >>>> things and doing so before expiry would greatly complicate testing.
> >>>>
> >>>> ==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 a "version bits" with an 80%(this can be
> >>>> adjusted if desired) activation threshold BIP9 with the name
> >>>> "segsignal" and using bit 4.
> >>>>
> >>>> This BIP will have a start time of midnight June 1st, 2017 (epoch time
> >>>> 1496275200) and timeout on midnight November 15th 2017 (epoch time
> >>>> 1510704000). 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);
> >>>> }
> >>>>
> >>>> // SEGSIGNAL mandatory segwit signalling.
> >>>> if ( VersionBitsState(pindex->pprev, chainparams.GetConsensus(),
> >>>> Consensus::DEPLOYMENT_SEGSIGNAL, versionbitscache) ==
> THRESHOLD_ACTIVE
> >>>> &&
> >>>>     !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:segsignal-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. Miners will need to upgrade their nodes to
> >>>> support segsignal otherwise they may build on top of an invalid block.
> >>>> While this bip is active users should either upgrade to segsignal 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.
> >>>>
> >>>> 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.
> >>>>
> >>>> ==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-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
> >
> > _______________________________________________
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