While I haven't rejected sidechains entirely yet, this particular proposal
seems uninteresting, especially for two reasons.
One – it introduces a new token for each sidechain and suggests atomic swaps to
be used for the exchange of the mainchain token with the sidechain token. Such
a model seems nonsensical to me because there seems to be excessive number of
blockchain projects that can be used similarly just as the sidechain in this
proposal. Pick almost any altcoin out there and you can atomic swap it with
Bitcoin. The fact that your sidechain is somehow mathematically bound to
Bitcoin seems arbitrary because at the end you have a new token and a new
issuance model. Therefore this is not extending Bitcoin economy, which is
strictly limited by its convergence to zero inflation. This proposal is
inflating the supply with a new token, which goes against what many people
consider as a pillar of Bitcoin's value proposal. I think if you implement this
proposal, you are going not to be considered as a Bitcoin sidechain, but you
will be, from certain point of view, indistinguishable from any other altcoin.
At the level of my current understanding, the only interesting sidechain model
is the [theoretical] one with a two way peg with Bitcoin, preserving the
issuance policy of Bitcoin.
Two – the security of the proposed system seems to be very fragile, unless I
have missed something. When I think about sidechains, I expect that it should
be possible to create a niche chain which is used by few participants while the
security of the chain is somehow guaranteed from its bind to the mainchain. If
this was not the case, such a niche sidechain could easily be attacked, even if
just stalled/censored for a long period time, with just a small [absolute]
investment from an attacker, although this investment might be large if taken
relatively to the utility of this niche sidechain. So if we speak concretely
about your proposal, you assume honest majority of validators. But in your
system the validators come from locking of stake on Bitcoin chain by nodes that
are interested in a particular sidechain. If you put this model on a niche
chain where only few participants are interested in it, it's trivial for an
attacker to be stronger [have more Bitcoin to lock] than all legitimate users
together. You should only use honest majority assumption where the scope is
global, where it is very hard and very expensive to obtain majority.
Sent with [ProtonMail](https://protonmail.com) Secure Email.
‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Sunday, January 12, 2020 6:54 PM, Robin Linus via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
> Hi all,
>
> I've been working on a sidechain protocol with no trusted third party. You
> can find the [whitepaper here](http://coins.github.io/coins.pdf).
>
> Abstract. Coins is a Bitcoin extension designed for payments at scale. We
> propose an efficient solution to the double-spending problem using a
> bitcoin-backed proof-of-stake. Validators vote on sidechain blocks with
> one-time signatures, forming a record that cannot be changed without
> destroying their collateral. Every user can become a validator by locking
> bitcoins. One-time signatures guarantee that validators loose their stake for
> publishing conflicting histories. Checkpoints can be additionally secured
> with a bitcoin-backed proof-of-burn. Assuming a rational majority of
> validators, the sidechain provides safety and liveness. The sidechain’s
> footprint within bitcoin’s blockchain is minimal. The protocol is a generic
> consensus mechanism allowing for arbitrary sidechain assets. Spawning
> multiple, independent instances scales horizontally.
>
> Feedback is highly appreciated!
>
> Thank you
>
> - Robin
>
> PS: [Here on Github you can find further research on scalability and
> usability](https://github.com/coins/coins.github.io).
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