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

[Wang Chun <1240902@gmail.com>]

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.
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> 
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