Subject: Re: [bitcoin-dev] Relative txout amounts with a Merkleized Sum Tree and explicit miner fee.

From: Rijndael <[email-masked]>
Date: Sat, 26 Nov 2022 00:12:10 +0000

Hello Andrew,

As ZmnSCPxj mentioned, covenant schemes are probably something that you
should be looking at and thinking about. In addition to CTV, I'd also
recommend you take a look (if you haven't already) at
`TAPLEAF_UPDATE_VERIFY`
(https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2021-September/019419.html).
 From your description, it sounds like you may be barking up a similar tree.

Rijndael

On 11/21/22 6:52 PM, ZmnSCPxj via bitcoin-dev wrote:
> Good morning Andrew,
>
>>
>> Can output amounts be mapped to a tap branch? For the goal of secure partial spends of a single UTXO? Looking for feedback on this idea. I got it from Taro.
>
> Not at all.
>
> The issue you are facing here is that only one tap branch will ever consume the entire input amount.
> That is: while Taproot has multiple leaves, only exactly one leaf will ever be published onchain and that gets the whole amount.
>
> What you want is multiple tree leaves where ALL of them will EVENTUALLY be published, just not right now.
>
> In that case, look at the tree structures for `OP_CHECKTEMPLATEVERIFY`, which are exactly what you are looking for, and help make `OP_CTV` a reality.
>
> Without `OP_CHECKTEMPLATEVERIFY` it is possible to use presigned transactions in a tree structure to do this same construction.
> Presigned transactions are known to be larger than `OP_CHECKTEMPLATEVERIFY` --- signatures on taproot are 64 bytes of witness, but an `OP_CHECKTEMPLATEVERIFY` in a P2WSH reveals just 32 bytes of witness plus the `OP_CHECKTEMPLATEVERIFY` opcode.
>
> Regards,
> ZmnSCPxj
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