Date: Fri, 18 Dec 2015 04:18:45 -0800
From: Peter Todd <pete@petertodd.org>
To: Eric Lombrozo <elombrozo@gmail.com>
Message-ID: <20151218121845.GB22789@muck>
References: <E76D5BF9-41BF-4AF5-BBAC-06F4EF574EBE@toom.im>
	<em9d607452-50c0-4aa2-941e-7b637a287a70@platinum>
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In-Reply-To: <em9d607452-50c0-4aa2-941e-7b637a287a70@platinum>
Cc: Bitcoin Dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] On the security of softforks
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On Fri, Dec 18, 2015 at 03:02:36AM +0000, Eric Lombrozo via bitcoin-dev wro=
te:
> First of all, that's an expensive beer!
>=20
> Second of all, any consensus rule change risks non-full-validating
> or non-upgraded nodes seeing invalid confirmations...but assuming a
> large supermajority (i.e. > 95%) of hashing power is behind the new
> rule, it is extremely unlikely that very many invalid confirmations
> will ever be seen by anyone. The number of confirmations you require

To clarify, because the 95% of upgraded hashing power is creating valid
blocks from the point of view of the remaining 5%, that 95% majority
will continually reorg the 5% non-upgrading chain. This ensures that the
invalid chain remains short, and thus the # of invalid confirmations
possible remains small. For instance, the chance of getting one invalid
confirmation is 0.05^1 =3D 5%, two invalid confirmations 0.05^2 =3D 0.25%, =
three
0.05^3 =3D 0.01% etc.

Whereas with a hard fork, the 5% of miners will continue mining on their
own chain. While that chain's length will increase more slowly than
normal, the # of confirmations that non-upgraded clients will see on it
are unbounded.


Anyway, we should write this up as a BIP - there's been a tremendous
amount of misinformation, even flat out lies, floating around on this
subject.

--=20
'peter'[:-1]@petertodd.org
000000000000000001bd68962863e6fa34e9776df361d4926912f52fc5f4b618

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