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Date: Fri, 5 Feb 2016 10:58:36 +0100
Message-ID: <CABm2gDpPZ6gcUncM3opPYft6+g=MH35xvboRfLaitju9DDyCxg@mail.gmail.com>
From: =?UTF-8?B?Sm9yZ2UgVGltw7Nu?= <jtimon@jtimon.cc>
To: Gavin Andresen <gavinandresen@gmail.com>
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Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Hardfork bit BIP
Precedence: list

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Concept ACK. I've been talking about adding this to BIP99 since before
scaling bitcoin Hong Kong, so it will be nice to have a BIP to just point
to. Also I hadn't thought about concurrent deployment of 2 hardforks, nice.

On Feb 4, 2016 23:30, "Gavin Andresen via bitcoin-dev" <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> If the worry is full nodes that are not upgraded, then a block with a
negative version number will, indeed, fork them off the the chain, in
exactly the same way a block with new hard-forking consensus rules would.
And with the same consequences (if there is any hashpower not paying
attention, then a worthless minority chain might continue on with the old
rules).

Additionally, a warning or special error could be thrown when a block is
rejected due to the hardfork bit being activated.

> I think a much better idea than this proposed BIP would be a BIP that
recommends that SPV clients to pay attention to block version numbers in
the headers that they download, and warn if there is a soft OR hard fork
that they don't know about.

Although I agree this PR should include such warning/error recommendations,
SPV nodes can't tell whether a change is a hardfork or a softfork just by
looking at the version bits, even in the case of uncontroversial hardforks
deployed with bip9 as recommended by bip99. For controversial hardforks
where bip9 should NOT be used for deployment, setting the hardfork bit is
even more important.

> It is also a very good idea for SPV clients to pay attention to
timestamps in the block headers that the receive, and to warn if blocks
were generated either much slower or faster than statistically likely.
Doing that (as Bitcoin Core already does) will mitigate Sybil attacks in
general.

This seems out of the scope of this PR.

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<p dir=3D"ltr">Concept ACK. I&#39;ve been talking about adding this to BIP9=
9 since before scaling bitcoin Hong Kong, so it will be nice to have a BIP =
to just point to. Also I hadn&#39;t thought about concurrent deployment of =
2 hardforks, nice.</p>
<p dir=3D"ltr">On Feb 4, 2016 23:30, &quot;Gavin Andresen via bitcoin-dev&q=
uot; &lt;<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-d=
ev@lists.linuxfoundation.org</a>&gt; wrote:</p>
<p dir=3D"ltr">&gt; If the worry is full nodes that are not upgraded, then =
a block with a negative version number will, indeed, fork them off the the =
chain, in exactly the same way a block with new hard-forking consensus rule=
s would. And with the same consequences (if there is any hashpower not payi=
ng attention, then a worthless minority chain might continue on with the ol=
d rules).</p>
<p dir=3D"ltr">Additionally, a warning or special error could be thrown whe=
n a block is rejected due to the hardfork bit being activated.<br></p>
<p dir=3D"ltr">&gt; I think a much better idea than this proposed BIP would=
 be a BIP that recommends that SPV clients to pay attention to block versio=
n numbers in the headers that they download, and warn if there is a soft OR=
 hard fork that they don&#39;t know about.</p>
<p dir=3D"ltr">Although I agree this PR should include such warning/error r=
ecommendations, SPV nodes can&#39;t tell whether a change is a hardfork or =
a softfork just by looking at the version bits, even in the case of uncontr=
oversial hardforks deployed with bip9 as recommended by bip99. For controve=
rsial hardforks where bip9 should NOT be used for deployment, setting the h=
ardfork bit is even more important.</p>
<p dir=3D"ltr">&gt; It is also a very good idea for SPV clients to pay atte=
ntion to timestamps in the block headers that the receive, and to warn if b=
locks were generated either much slower or faster than statistically likely=
. Doing that (as Bitcoin Core already does) will mitigate Sybil attacks in =
general.</p>
<p dir=3D"ltr">This seems out of the scope of this PR.<br>
</p>

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