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

Tue May 23 20:42:46 UTC 2017

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 at 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 at 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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>> bitcoin-dev at lists.linuxfoundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
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