Discussion:
Reduced signalling threshold activation of existing segwit deployment
(too old to reply)
James Hilliard via bitcoin-dev
2017-05-22 22:40:13 UTC
Permalink
Raw Message
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 <***@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.
Matt Corallo via bitcoin-dev
2017-05-22 22:43:00 UTC
Permalink
Raw Message
Given the overwhelming support for SegWit across the ecosystem of businesses and users, this seems reasonable to me.
Post by James Hilliard via bitcoin-dev
I would like to propose an implementation that accomplishes the first
"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.
https://github.com/jameshilliard/bips/blob/bip-segsignal/bip-segsignal.mediawiki
<pre>
BIP: segsignal
Layer: Consensus (soft fork)
Title: Reduced signalling threshold activation of existing segwit deployment
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
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Erik Aronesty via bitcoin-dev
2017-05-23 04:00:53 UTC
Permalink
Raw Message
Seems like it would work fine. But why would we expect 80pct to signal for
the exact same implementation - when we can't get 40pct.

It will be contingent on some HF code that allows him to continue using
asicboost, or is too aggressive, or some other unreasonable request.



On May 22, 2017 6:43 PM, "Matt Corallo via bitcoin-dev" <
bitcoin-***@lists.linuxfoundation.org> wrote:

Given the overwhelming support for SegWit across the ecosystem of
businesses and users, this seems reasonable to me.

On May 22, 2017 6:40:13 PM EDT, James Hilliard via bitcoin-dev <
Post by James Hilliard via bitcoin-dev
I would like to propose an implementation that accomplishes the first
"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.
https://github.com/jameshilliard/bips/blob/bip-segsignal/bip-segsignal.
mediawiki
Post by James Hilliard via bitcoin-dev
<pre>
BIP: segsignal
Layer: Consensus (soft fork)
Title: Reduced signalling threshold activation of existing segwit deployment
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
Post by James Hilliard via bitcoin-dev
==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
Post by James Hilliard via bitcoin-dev
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
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Kekcoin via bitcoin-dev
2017-05-23 09:51:19 UTC
Permalink
Raw Message
I think there may be merit to this idea, allowing for political compromise without sacrificing the technological integrity of Bitcoin. There are a few mechanical problems I see with it, though.

1. It should change its activation logic from BIP9-style to BIP8-style with a flagday of August 1. This to maintain backwards compatibility with the current deployment of BIP148 nodes. This proposal seems to be a measure to prevent a chainsplit, so it must make sure to avoid triggering one.

2. This should be for miners only; non-miners should not enforce this. It severely weakens the block-signalling activation mechanism in several ways (lowered threshold, short deployment timeframe, no "locked in" delay before activation) and by doing so opens up attack vectors for consensus-partitioning attacks using malicious false signalling. For non-miners that seek to take their fate into their own hands, enforcing BIP148 is enough.

3. Even for miners this is more risky than usual; only 31% of hashrate is required to false-signal the activation to fork-off honest miners. This attack vector is magnified by the lack of "locked in" delay that would allow laggards to upgrade before activation. I suggest adding in at least a 1-week lock-in period (given the shorter timeframes 2 weeks may eat up too much of the available voting time before the brick wall of BIP148 activation on August 1).

Under the assumption that this is indeed compatible with the terms of the Silbert agreement, we can presume the involved miners are willing to trust eachother more than usual so such a short lock-in period should be acceptable.

-------- Original Message --------
Subject: [bitcoin-dev] Reduced signalling threshold activation of existing segwit deployment
Local Time: May 23, 2017 1:40 AM
UTC Time: May 22, 2017 10:40 PM
From: bitcoin-***@lists.linuxfoundation.org
To: Bitcoin Dev <bitcoin-***@lists.linuxfoundation.org>

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 <***@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.
James Hilliard via bitcoin-dev
2017-05-23 16:56:51 UTC
Permalink
Raw Message
Post by Kekcoin via bitcoin-dev
I think there may be merit to this idea, allowing for political compromise
without sacrificing the technological integrity of Bitcoin. There are a few
mechanical problems I see with it, though.
1. It should change its activation logic from BIP9-style to BIP8-style with
a flagday of August 1. This to maintain backwards compatibility with the
current deployment of BIP148 nodes. This proposal seems to be a measure to
prevent a chainsplit, so it must make sure to avoid triggering one.
That can be done as a separate proposal, it's not mutually exclusive
to this one for those who intend to run BIP148.
Post by Kekcoin via bitcoin-dev
2. This should be for miners only; non-miners should not enforce this. It
severely weakens the block-signalling activation mechanism in several ways
(lowered threshold, short deployment timeframe, no "locked in" delay before
activation) and by doing so opens up attack vectors for
consensus-partitioning attacks using malicious false signalling. For
non-miners that seek to take their fate into their own hands, enforcing
BIP148 is enough.
I disagree that it should be only run by miners, enforcement of
segsignal mandatory signalling by economic nodes strongly discourages
any false signaling.
Post by Kekcoin via bitcoin-dev
3. Even for miners this is more risky than usual; only 31% of hashrate is
required to false-signal the activation to fork-off honest miners. This
attack vector is magnified by the lack of "locked in" delay that would allow
laggards to upgrade before activation. I suggest adding in at least a 1-week
lock-in period (given the shorter timeframes 2 weeks may eat up too much of
the available voting time before the brick wall of BIP148 activation on
August 1).
Those who can should still upgrade for segsignal, the more that
upgrade ahead of activation the more secure it is. Those who don't
upgrade would want to wait for more confirmations anyways. I didn't
think a lock in period was all that good an idea here due to the
fairly short deployment timeline.
Post by Kekcoin via bitcoin-dev
Under the assumption that this is indeed compatible with the terms of the
Silbert agreement, we can presume the involved miners are willing to trust
eachother more than usual so such a short lock-in period should be
acceptable.
-------- Original Message --------
Subject: [bitcoin-dev] Reduced signalling threshold activation of existing
segwit deployment
Local Time: May 23, 2017 1:40 AM
UTC Time: May 22, 2017 10:40 PM
I would like to propose an implementation that accomplishes the first
"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.
https://github.com/jameshilliard/bips/blob/bip-segsignal/bip-segsignal.mediawiki
<pre>
BIP: segsignal
Layer: Consensus (soft fork)
Title: Reduced signalling threshold activation of existing segwit deployment
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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