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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable mm you are right, then the "moving checkpoint" rule needs to have some limi= ts to allow the network self-heal instead of requiring humans detecting the= splits or stopping nodes. Let's suppose than a 51% attack can be detected and the developers can rele= ase a new version of the software with a new mining protocol in about 3 day= s. Then the complementary rule could be something like this: - If 2 forks have a block height difference of 432 blocks (about 3 days) or= more, then the moving checkpoint rule is ignored and everything works as w= ith the current protocol. With this rule, the network can self-heal in a 10= 0% automated way. This would prevent a history rewrite of more than 24 hours during a 51% att= ack during 3 days, which should give enough time to change the protocol. If= instead of a 51% attack what happens is a network split, then nodes should= converge to the longest chain in a few days. But maybe I'm missing something here, I'm still learning. Regards, ________________________________ From: Alistair Mann Sent: Thursday, August 1, 2019 1:28 To: Kenshiro [] Cc: Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] Add a moving checkpoint to the Bitcoin protocol On Wednesday 31 Jul 2019 14:53:25 Kenshiro [] wrote: >> How would a (potentially, state-sponsored) netsplit lasting longer than >> N be handled? > > It would be detected by the community much before reaching the reorg limi= t > of N blocks (it's 24 hours) so nodes could stop until the netsplit is > fixed. A netsplit cannot be detected but merely be suspected where the p2p protoco= l does allow arbitrary connecting/disconnecting of any peer: there's no difference between a remote net being split off, that net having nothing to say, and that net choosing to disconnect. Detection then mandates manual, o= ut- of-band communications, which is error prone and centralising. I also observe 'stopping nodes' during netsplits introduces several attack vectors. Among them: create a netsplit, which stops the nodes, turn off the netsplit, repeat. A sequence of 365 actors causing their own small netsplit= s could effectively stop Bitcoin at the cost (to them) of no Internet for one day a year as the rolling netsplit could never be fixed. > In the extreme case no one notice the network split during more than N > blocks (24 hours) and there are 2 permanent forks longer than N, nodes fr= om > one branch could delete their local history so they would join the other > branch. > > P.S.: To be clearer, in this example I set an N value of 144 blocks, whic= h > is approximately 24 hours. I've seen estimates of China hosting more than 51% of hashpower. Say they conduct a netsplit. Does your suggestion mean that it's the rest of the wor= ld that has to delete their local history because they lack the hashpower to assert themselves as the proper branch? If so, I think having to delete act= ual history everywhere across the globe but China is not a price worth paying t= o limit reorgs to 24 hours. I am unconvinced that the moving checkpoint you describe would improve Bitcoin. -- Alistair Mann --_000_DB6PR10MB1832679F3A195358D234111CA6DE0DB6PR10MB1832EURP_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
mm you are right, then the "moving checkpoint" rule needs to have= some limits to allow the network self-heal instead of requiring humans det= ecting the splits or stopping nodes. 

Let's suppose than a 51% attack can be detected and the developers can rele= ase a new version of the software with a new mining protocol in about 3 day= s. Then the complementary rule could be something like this:

- If 2 forks have a bloc= k height difference of 432 blocks (about 3 days) or more, then the moving checkpoint rule is igno= red and everything works as with the current protocol. With this rule, the = network can self-heal in a 100% automated way.

This would prevent a his= tory rewrite of more than 24 hours during a 51% attack during 3 days, which= should give enough time to change the protocol. If instead of a 51% attack what happens is a network split, = then nodes should converge to the longest chain in a few days.

But maybe I'm missing so= mething here, I'm still learning.

Regards,



From: Alistair Mann <al@= pectw.net>
Sent: Thursday, August 1, 2019 1:28
To: Kenshiro [] <tensiam@hotmail.com>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundatio= n.org>
Subject: Re: [bitcoin-dev] Add a moving checkpoint to the Bitcoin pr= otocol
 
On Wednesday 31 Jul 2019 14:53:25 Kenshiro [] wrot= e:
>> How would a (potentially, state-sponsored) netsplit lasting longer= than
>> N be handled?
>
> It would be detected by the community much before reaching the reorg l= imit
> of N blocks (it's 24 hours) so nodes could stop until the netsplit is<= br> > fixed.

A netsplit cannot be detected but merely be suspected where the p2p protoco= l
does allow arbitrary connecting/disconnecting of any peer: there's no
difference between a remote net being split off, that net having nothing to=
say, and that net choosing to disconnect. Detection then mandates manual, o= ut-
of-band communications, which is error prone and centralising.

I also observe 'stopping nodes' during netsplits introduces several attack =
vectors. Among them: create a netsplit, which stops the nodes, turn off the=
netsplit, repeat. A sequence of 365 actors causing their own small netsplit= s
could effectively stop Bitcoin at the cost (to them) of no Internet for one=
day a year as the rolling netsplit could never be fixed.

> In the extreme case no one notice the network split during more than N=
> blocks (24 hours) and there are 2 permanent forks longer than N, nodes= from
> one branch could delete their local history so they would join the oth= er
> branch.
>
> P.S.: To be clearer, in this example I set an N value of 144 blocks, w= hich
> is approximately 24 hours.

I've seen estimates of China hosting more than 51% of hashpower. Say they <= br> conduct a netsplit. Does your suggestion mean that it's the rest of the wor= ld
that has to delete their local history because they lack the hashpower to <= br> assert themselves as the proper branch? If so, I think having to delete act= ual
history everywhere across the globe but China is not a price worth paying t= o
limit reorgs to 24 hours.

I am unconvinced that the moving checkpoint you describe would improve
Bitcoin.
--
Alistair Mann
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