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From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
To: Erik Aronesty <erik@q32.com>
Cc: Bitcoin Protocol Discussion
	<bitcoin-dev@lists.linuxfoundation.org>,
	Anthony Towns <aj@erisian.com.au>
Subject: Re: [bitcoin-dev] `OP_EVICT`: An Alternative to `OP_TAPLEAFUPDATEVERIFY`
Date: Fri, 18 Feb 2022 16:06:39 +0000	[thread overview]
Message-ID: <3YGc8zgpxTXfmj09vOFSHiGqubBn5Tb6PefbEje8vbSvcKt3wWlf2Ue1VCS33WFygsLq5Rvdv9FW8SCvoDqGNUVYT7gAa2z4NSdu5GHqkHc=@protonmail.com> (raw)
In-Reply-To: <CAJowKgKEAptvQnOSKc7W=FDtf6DRchaBUyx3QWeHbCN_89w2zQ@mail.gmail.com>

Good morning Erik,

> > As I understand your counterproposal, it would require publishing one transaction per evicted participant.
>
> if you also pre-sign (N-2, N-3, etc), you can avoid this

It also increases the combinatorial explosion.

> > In addition, each participant has to store `N!` possible orderings in which participants can be evicted, as you cannot predict the future and cannot predict which partiicpants will go offline first.
>
> why would the ordering matter?  these are unordered pre commitments to move funds, right?   you agree post the one that represents "everyone that's offline"

Suppose `B` is offline first, then the remaining `A` `C` and `D` publish the eviction transaction that evicts only `B`.
What happens if `C` then goes offline?
We need to prepare for that case (and other cases where the participants go offline at arbitrary orders) and pre-sign a spend from the `ACD` set and evicts `C` as well, increasing combinatorial explosion.
And so on.

We *could* use multiple Tapleaves, of the form `<A> OP_CHECKSIG <BCD> OP_CHECKSIG` for each participant.
Then the per-participant `<A>` signature is signed with `SIGHASH_SINGLE|SIGHASH_ANYONECANPAY` and is pre-signed, while the remainder is signed by `<BCD>` with default `SIGHASH_ALL`.
Then if one participant `B` is offline they can evict `B` and then the change is put into a new UTXO with a similar pre-signed scheme `<A> OP_CHECKSIG <CD> OP_CHECKSIG`.
This technique precludes pre-signing multiple evictions.

>
> > But yes, certainly that can work, just as pre-signed transactions can be used instead of `OP_CTV` 
>
> i don't see how multiple users can securely share a channel (allowing massive additional scaling with lighting) without op_ctv

They can, they just pre-sign, like you pointed out.
The same technique works --- `OP_CTV` just avoids having ridiculous amounts of combinatorial explosion and just requires `O(log n)` per eviction.
Remember, this proposal can be used for channel factories just as well, as pointed out, so any objection to this proposal also applies to `OP_CTV`.



Regards,
ZmnSCPxj


  reply	other threads:[~2022-02-18 16:06 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-18  2:45 [bitcoin-dev] `OP_EVICT`: An Alternative to `OP_TAPLEAFUPDATEVERIFY` ZmnSCPxj
2022-02-18 13:53 ` Erik Aronesty
2022-02-18 14:48   ` ZmnSCPxj
2022-02-18 15:50     ` Erik Aronesty
2022-02-18 16:06       ` ZmnSCPxj [this message]
2022-02-18 13:55 ` Jonas Nick
2022-02-18 18:09 ` Antoine Riard
2022-02-18 23:39   ` ZmnSCPxj
2022-02-19  0:56     ` Jeremy Rubin
2022-02-19  1:17       ` ZmnSCPxj
2022-02-19  1:46       ` Greg Sanders
2022-02-19  7:21         ` Billy Tetrud
2022-02-19 11:41           ` ZmnSCPxj
2022-02-19 21:59             ` Billy Tetrud
2022-02-22  0:17     ` Antoine Riard
2022-02-23 11:42       ` ZmnSCPxj

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