Subject: Re: [bitcoin-dev] Statechain implementations

From: "David A. Harding" <[email-masked]>
Date: Tue, 31 Mar 2020 06:35:08 -0400

On Wed, Mar 25, 2020 at 01:52:10PM +0000, Tom Trevethan via bitcoin-dev wrote:
> Hi all,
> 
> We are starting to work on an implementation of the statechains concept (
> https://medium.com/@RubenSomsen/statechains-non-custodial-off-chain-bitcoin-transfer-1ae4845a4a39),
>
> [...]
> There are two main modifications we are looking at:
> [...]
> 
> 2. Replacing the 2-of-2 multisig output (paying to statechain entity SE key
> and transitory key) with a single P2(W)PKH output where the public key
> shared between the SE and the current owner. The SE and the current owner
> can then sign with a 2-of-2 ECDSA MPC. 

Dr. Trevethan,

Would you be able to explain how your proposal to use statechains with
2P-ECDSA relates to your patent assigned to nChain Holdings for "Secure
off-chain blockchain transactions"?[1]  

    [1] https://patents.google.com/patent/US20200074464A1

Here are some excerpts from the application that caught my attention in
the context of statechains in general and your proposal to this list in
particular:

> an exchange platform that is trusted to implement and operate the
> transaction protocol, without requiring an on-chain transaction. The
> off-chain transactions enable one computer system to generate multiple
> transactions that are recordable to a blockchain in different
> circumstances
>
> [...]
>
> at least some of the off-chain transactions are valid for recording on
> the blockchain even in the event of a catastrophic failure of the
> exchange (e.g., exchange going permanently off-line or loosing key
> shares).
>
> [...]
>
> there may be provided a computer readable storage medium including a
> two-party elliptic curve digital signature algorithm (two-party ECDSA)
> script comprising computer executable instructions which, when
> executed, configure a processor to perform functions of a two-party
> elliptic curve digital signature algorithm described herein.
>
> [...]
>
> In this instance the malicious actor would then also have to collude
> with a previous owner of the funds to recreate the full key. Because
> an attack requires either the simultaneous theft of both exchange and
> depositor keys or collusion with previous legitimate owners of funds,
> the opportunities for a malicious attacker to compromise the exchange
> platform are limited.

Thank you,

-Dave