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

Tue May 23 20:58:14 UTC 2017

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