Subject: Re: [bitcoin-dev] Ark: An Alternative Privacy-preserving Second Layer Solution

From: Burak Keceli <[email-masked]>
Date: Wed, 7 Jun 2023 16:30:07 +0300 (TRT)

> A problem with the idea of using one-show signatures as double-spend
> protection is that miner-claimable fidelity bonds don't work as well
> against adversaries that are not just counterparties but also miners
> themselves. 

Hey David,

The fidelity bonds in the Ark context are nothing but the vTXOs themselves, which in simple terms, have two possible closures: (1) a key-path collaborative closure with higher precedence and (2) a script-path closure with lower precedence.

The key-path closure is a 2-of-2 between the rightful owner of the vTXO and the service provider. The script path closure, on the other hand, lets the service provider sweep funds after a relative lock time. The key-path closure has higher precedence over the script-path closure since it can be triggered immediately with a satisfying signature.

If the service provider double-spends a transaction that enforces a one-time signature where Bob is the vendor, Bob can forge the service provider’s signature from the 2-of-2 and can immediately claim his previously-spent vTXO(s). If Alice (or the service provider) is a miner she won’t be able steal funds regardless, since she won’t be able co-sign from the Bob’s key.

Best,
Burak