Re: [bitcoin-dev] Introducing a POW through a soft-fork

From: Eric Voskuil <eric@voskuil•org>
To: Paul Sztorc <truthcoin@gmail•com>,
	Bitcoin Protocol Discussion
	<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Introducing a POW through a soft-fork
Date: Mon, 6 Nov 2017 12:55:29 -0800	[thread overview]
Message-ID: <61253DDB-A045-4346-A39C-F5C4E07396C7@voskuil.org> (raw)
In-Reply-To: <CA+XQW1j2vNNswEQ-HVWF9MpyGBzmq3ij+v=2NGH2VicQ63=v6A@mail.gmail.com>

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If a block that would be discarded under previous rules becomes accepted after a rule addition, there is no reason to not simply call the new rule a hard fork. IOW it's perfectly rational to consider a weaker block as "invalid" relative to the strong chain. As such I don't see any reason to qualify the term, it's a hard fork. But Peter's observation (the specific behavior) is ultimately what matters.

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> On Nov 6, 2017, at 12:30, Paul Sztorc via bitcoin-dev <bitcoin-dev@lists•linuxfoundation.org> wrote:
> 
> +1 to all of Peter Todd's comments
> 
>> On Nov 6, 2017 11:50 AM, "Peter Todd via bitcoin-dev" <bitcoin-dev@lists•linuxfoundation.org> wrote:
>> On Wed, Nov 01, 2017 at 05:48:27AM +0000, Devrandom via bitcoin-dev wrote:
>> 
>> Some quick thoughts...
>> 
>> > Hi all,
>> >
>> > Feedback is welcome on the draft below.  In particular, I want to see if
>> > there is interest in further development of the idea and also interested in
>> > any attack vectors or undesirable dynamics.
>> >
>> > (Formatted version available here:
>> > https://github.com/devrandom/btc-papers/blob/master/aux-pow.md )
>> >
>> > # Soft-fork Introduction of a New POW
>> 
>> First of all, I don't think you can really call this a soft-fork; I'd call it a
>> "pseudo-soft-fork"
>> 
>> My reasoning being that after implementation, a chain with less total work than
>> the main chain - but more total SHA256^2 work than the main chain - might be
>> followed by non-supporting clients. It's got some properties of a soft-fork,
>> but it's security model is definitely different.
>> 
>> > ### Aux POW intermediate block
>> >
>> > Auxiliary POW blocks are introduced between normal blocks - i.e. the chain
>> > alternates between the two POWs.
>> > Each aux-POW block points to the previous normal block and contains
>> > transactions just like a normal block.
>> > Each normal block points to the previous aux-POW block and must contain all
>> > transactions from the aux-POW block.
>> 
>> Note how you're basically proposing for the block interval to be decreased,
>> which has security implications due to increased orphan rates.
>> 
>> > ### Heaviest chain rule change
>> >
>> > This is a semi-hard change, because non-upgraded nodes can get on the wrong
>> > chain in case of attack.  However,
>> 
>> Exactly! Not really a soft-fork.
>> 
>> --
>> https://petertodd.org 'peter'[:-1]@petertodd.org
>> 
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