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

[James Hilliard <james.hilliard1@gmail.com>]

I would be fine with that, since segwit is widely deployed on the
network already a lower activation threshold should be safe.

On Wed, May 24, 2017 at 12:02 PM, Wang Chun <1240902@gmail.com> 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
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