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From: Erik Aronesty <erik@q32.com>
Date: Fri, 18 Feb 2022 10:50:02 -0500
Message-ID: <CAJowKgKEAptvQnOSKc7W=FDtf6DRchaBUyx3QWeHbCN_89w2zQ@mail.gmail.com>
To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Content-Type: multipart/alternative; boundary="000000000000b206c205d84cd609"
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`
Precedence: list

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> 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

> 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"

> 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


On Fri, Feb 18, 2022 at 9:48 AM ZmnSCPxj <ZmnSCPxj@protonmail.com> wrote:

> Good morning Erik,
>
> > hey, i read that whole thing, but i'm confused as to why it's necessary
> >
> > seems like N of N participants can pre-sign an on-chain transfer of
> funds for each participant to a new address that consists of (N-1) or (N-1)
> participants, of which each portion of the signature is encrypted for the
> same (N-1) participants
> >
> > then any (N-1) subset of participants can collude publish that
> transaction at any time to remove any other member from the pool
> >
> > all of the set up  (dkg for N-1), and transfer (encryption of partial
> sigs) is done offchain, and online with the participants that are online
>
>
> As I understand your counterproposal, it would require publishing one
> transaction per evicted participant.
> 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.
>
> Finally, please see also the other thread on lightning-dev:
> https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-February/003479.html
> In this thread, I point out that if we ever use channel factories, it
> would be best if we treat each channel as a 2-of-2 that participates in an
> overall N-of-N (i.e. the N in the outer channel factory is composed of
> 2-of-2).
> For example, instead of the channel factory being signed by participants
> `A`, `B`, `C`, `D`, instead the channel factory is signed by `AB`, `AC`,
> `AD`, `BC`, `BD`, `CD`, so that if e.g. participant B needs to be evicted,
> we can evict the signers `AB`, `BC`, and `BD`.
> This means that for the channel factory case, already the number of
> "participants" is quadratic on the number of *actual* participants, which
> greatly increases the number of transactions that need to be evicted in
> one-eviction-at-a-time schemes (which is how I understand your proposal) as
> well as increasing the `N!` number of signatures that need to be exchanged
> during setup.
>
>
> But yes, certainly that can work, just as pre-signed transactions can be
> used instead of `OP_CTV` or pretty much any non-`OP_CHECKMULTISIG` opcode,
> xref Smart Contracts Unchained.
>
> Regards,
> ZmnSCPxj
>

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<div dir=3D"ltr">&gt; As I understand your counterproposal, it would requir=
e publishing one transaction per evicted participant.<div><br></div><div>if=
 you also pre-sign (N-2, N-3, etc), you can avoid this<br><div><br>&gt; In =
addition, each participant has to store `N!` possible orderings in which pa=
rticipants can be evicted, as you cannot predict the future and cannot pred=
ict which partiicpants will go offline first.<br></div><div><br>why would=
=C2=A0the ordering matter?=C2=A0 these are unordered pre commitments to mov=
e funds, right?=C2=A0 =C2=A0you agree post the one that represents &quot;ev=
eryone that&#39;s offline&quot;</div><div><br>&gt; But yes, certainly that =
can work, just as pre-signed transactions can be used instead of `OP_CTV`=
=C2=A0<br><br>i don&#39;t see how multiple users can securely share a chann=
el (allowing massive additional scaling with lighting) without op_ctv<br><b=
r></div></div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=
=3D"gmail_attr">On Fri, Feb 18, 2022 at 9:48 AM ZmnSCPxj &lt;<a href=3D"mai=
lto:ZmnSCPxj@protonmail.com">ZmnSCPxj@protonmail.com</a>&gt; wrote:<br></di=
v><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;borde=
r-left:1px solid rgb(204,204,204);padding-left:1ex">Good morning Erik,<br>
<br>
&gt; hey, i read that whole thing, but i&#39;m confused as to why it&#39;s =
necessary<br>
&gt;<br>
&gt; seems like N of N participants can pre-sign an on-chain transfer of fu=
nds for each participant to a new address that consists of (N-1) or (N-1) p=
articipants, of which each portion of the signature is encrypted for the sa=
me (N-1) participants<br>
&gt;<br>
&gt; then any (N-1) subset of participants can collude publish that transac=
tion at any time to remove any other member from=C2=A0the pool<br>
&gt;<br>
&gt; all of the set up=C2=A0 (dkg for N-1), and transfer (encryption of par=
tial sigs) is done offchain, and online with the participants=C2=A0that are=
 online<br>
<br>
<br>
As I understand your counterproposal, it would require publishing one trans=
action per evicted participant.<br>
In addition, each participant has to store `N!` possible orderings in which=
 participants can be evicted, as you cannot predict the future and cannot p=
redict which partiicpants will go offline first.<br>
<br>
Finally, please see also the other thread on lightning-dev: <a href=3D"http=
s://lists.linuxfoundation.org/pipermail/lightning-dev/2022-February/003479.=
html" rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.or=
g/pipermail/lightning-dev/2022-February/003479.html</a><br>
In this thread, I point out that if we ever use channel factories, it would=
 be best if we treat each channel as a 2-of-2 that participates in an overa=
ll N-of-N (i.e. the N in the outer channel factory is composed of 2-of-2).<=
br>
For example, instead of the channel factory being signed by participants `A=
`, `B`, `C`, `D`, instead the channel factory is signed by `AB`, `AC`, `AD`=
, `BC`, `BD`, `CD`, so that if e.g. participant B needs to be evicted, we c=
an evict the signers `AB`, `BC`, and `BD`.<br>
This means that for the channel factory case, already the number of &quot;p=
articipants&quot; is quadratic on the number of *actual* participants, whic=
h greatly increases the number of transactions that need to be evicted in o=
ne-eviction-at-a-time schemes (which is how I understand your proposal) as =
well as increasing the `N!` number of signatures that need to be exchanged =
during setup.<br>
<br>
<br>
But yes, certainly that can work, just as pre-signed transactions can be us=
ed instead of `OP_CTV` or pretty much any non-`OP_CHECKMULTISIG` opcode, xr=
ef Smart Contracts Unchained.<br>
<br>
Regards,<br>
ZmnSCPxj<br>
</blockquote></div>

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