Date: Fri, 17 Jan 2020 13:54:50 +0000
To: Robin Linus <robinlinus@protonmail.com>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
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Subject: Re: [bitcoin-dev] Coins: A trustless sidechain protocol
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Good morning Robin,

> Hi Joachim,=C2=A0
>
> > if anyone can halt operation of a sidechain with just tiny investment.
>
> It'll be impossible to halt a healthy chain with a tiny investment becaus=
e halting a chain costs you at least as much as the side chain rewards. The=
 "invested time value per block" of all honest stakers converges against th=
e block reward. If imbalanced, someone will stake more bitcoin to get the c=
heap sidechain rewards. Exactly the same market mechanism secures PoW.
>
> For a decentralized consensus via resource consumption it doesn't matter =
which limited resource you consume. The only relevant factor is that the va=
lue of the block reward is sufficient to motivate people to invest a lot of=
 that resource. To motivate them to invest so much that an attacker cannot =
invest more. Independently of the resource, the amount of honestly invested=
 resources converges against the value of the block reward.

Also known as MC =3D MR.

This is in fact the core of the argument *against* this kind of global micr=
ochain system: each individual chain will either:

* Pay ridiculously high fees per transaction, because the microchain has a =
small number of transactions because that is the entire *point* of microcha=
ins.
* Pay insufficient fees per block, making it easy to attack, meaning the se=
curity of the chain has to be centralized around a few actors anyway (e.g. =
checkpoints, like what every altcoin implements), which is not much better =
than the custodial case you are complaining against.

In order to have a sidechain that is as secure as Bitcoin today, you need:

* Sidechain fees to cover both *current Bitcoin fees* plus *current Bitcoin=
 block rewards*.

Consequently, the sidechain has to have either *more* users than Bitcoin to=
day, or *higher* fees than Bitcoin today.

Unless of course you propose to have the sidechain issue its own coin, in w=
hich case it is not much more than an altcoin.
Still, the real-world value of the total block rewards for that altcoin wil=
l have to match the real-world value of the total block rewards of Bitcoin =
in order to have security even approaching Bitcoin.

>
> Thus, I would even go further with my claim and argue that the security o=
f bitcoin-backed PoS is exactly as strong as PoW because in both cases thei=
r security is proportionally to the dollar value of their block reward. PoS=
 sidechain security depends only on a sufficient userbase and thus, block r=
eward value.

Only if the consumed resource matches what is consumed under PoW.
Otherwise it is not much better than a low-PoW altcoin, i.e. easily attacka=
ble unless it centralizes around the developers.


I understand the desire to smoothen the experience of onboarding new users =
to Bitcoin.
But this path is not much better than the custodial solutions you are tryin=
g to avoid anyway.

Regards,
ZmnSCPxj