From: Luke Dashjr <luke@dashjr.org>
To: bitcoin-dev@lists.linuxfoundation.org,
	Jorge =?iso-8859-1?q?Tim=F3n?= <jtimon@jtimon.cc>
Date: Fri, 2 Dec 2016 04:18:21 +0000
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Message-Id: <201612020418.23011.luke@dashjr.org>
Subject: Re: [bitcoin-dev] New BIP: Hardfork warning system
Precedence: list

On Friday, December 02, 2016 1:42:46 AM Jorge Tim=F3n via bitcoin-dev wrote:
> We can already warn users of a hardfork when a block is invalid (at
> least) because of the highest bit in nVersion (as you say, because it
> is forbidden since bip34 was deployed).

The difference is that right now, full nodes will happily follow a shorter=
=20
best-valid chain. This BIP would require them to hold back at the best-comm=
on=20
block between the best-valid chain and the invalid chain, forcing the user =
to=20
make a decision whether to reject the invalid chain permanently, or upgrade=
 to=20
a version which can understand that chain as valid.

> It seems the softfork serves only to warn about soft-hardforks, assuming =
it
> chooses to use this mechanism (which a malicious soft hardfork may not do=
).

Note: a malicious "SHF" is not a SHF at all, but an "evil fork".

> In fact, you could reuse another of the prohibited bits to signal a soft-
> hardfork while distinguishing it from a regular hardfork. And this will a=
lso
> serve for old nodes that have not upgraded to the softfork. But, wait,
> if you signal a soft-hardfork with an invalid bit, it's not a
> soft-hardfork anymore, is it? It's simply a hardfork.

Nodes implementing this BIP will see it as a simple hardfork, but will=20
intentionally provide equivalent behaviour as older nodes which see it as a=
=20
soft-hardfork. In other words, all [compatible] hardforks will now behave l=
ike=20
a soft-hardfork without any special DMMS design.

If Bitcoin's eventual hardfork is far enough down the road (such that no no=
des=20
remain from before this BIP are adopted), the SHF design could be safely do=
ne=20
away with entirely. And either way, it makes it easier to resist an un-
consented-to hardfork.

Luke