Return-Path: Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id 84F0EC0177 for ; Mon, 24 Feb 2020 18:27:07 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 6CB862051C for ; Mon, 24 Feb 2020 18:27:07 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id hF8H4IAkDAcB for ; Mon, 24 Feb 2020 18:27:05 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-pj1-f66.google.com (mail-pj1-f66.google.com [209.85.216.66]) by silver.osuosl.org (Postfix) with ESMTPS id 154BC20500 for ; Mon, 24 Feb 2020 18:27:05 +0000 (UTC) Received: by mail-pj1-f66.google.com with SMTP id 12so114654pjb.5 for ; Mon, 24 Feb 2020 10:27:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=tjvljFNG1wzZrQameEXm2Q2FADZ/qylV22JJFju+Ijw=; b=YzZ+GVq/SdyAplxUcsOAj/vh+2ML8ugeVaInUWaQo9iJz+h/+m1OYBQn88CnNzrZBC +fCP5tWXwmXlyzh+0Vv+c0DHuYYzAW1QuiWT53IC1VTKMf0qo3R9aO6036LTwGIz0hTj DipdlA3lr5Ns2L+6ZVnCunKw90vO9RnIQ2xJRx67Gp0R/Yp/NiGtVLhr9ZTZ4HLh9fWO C2Gwjqw8Dan8BrUmFMuo3eclndHa/jRHzHmSoOmn++XYUEORcfV2IVVra+b5Rqi4u4tF u9NQrVSM/m01vJfRZcWGC0sHUkAQAL3xORmb/8rz4jaECxvMglBf4IwQVnTdB7eQe82V g97g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=tjvljFNG1wzZrQameEXm2Q2FADZ/qylV22JJFju+Ijw=; b=a6lf0sIrwFg7CTjLZFI0kuMlJj6kOgHcylT06Hms6n+eMw6GsRUIIjOtXrxpAzSMlp TIau+nvgfqWMqXFGNMPghTrYSFCkgbfEP7lfwzjXN9WA/ycyu4k1hoerlhAzrkm2LV7B vMwIn/BzpdwNgSdOGbkrHiq3jK/Ym/uThROu17+QEKI/G+duC7QDFMNzK3DZDdcJIoYI U2v6BwpQWtMfQMkDWW2UTbtMKch29euZ0KFVRKaZViGus4GfUjVmzvNKqYamclw69WeO 8h0BMYWMppyTwPs4mPk5vLZ54WianQvI2mdyR+7y4u5m+mTCp1kNPtSuZa1ujp/tP4Gm 7elg== X-Gm-Message-State: APjAAAX3pLqwO+mrGbpu8zDOGCK1C+366rptkriVKNF/3wa1HsbZufId HDH84cgyZoRnqpfWvAN/YLs7iwbMKMqAR467fhs= X-Google-Smtp-Source: APXvYqyeNxueFH517vqHj6q0TjmWw9rBgIyyxU6ySM///Z9gIsT/owKyo2haIxatd+VSzg+c8C+oJt4YBNBvmBrLuq8= X-Received: by 2002:a17:90a:2004:: with SMTP id n4mr482617pjc.20.1582568824529; Mon, 24 Feb 2020 10:27:04 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Antoine Riard Date: Mon, 24 Feb 2020 13:26:52 -0500 Message-ID: To: ZmnSCPxj Content-Type: multipart/alternative; boundary="0000000000009e66e0059f5684dc" X-Mailman-Approved-At: Mon, 24 Feb 2020 18:40:40 +0000 Cc: Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] LN & Coinjoin, a Great Tx Format Wedding X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 24 Feb 2020 18:27:07 -0000 --0000000000009e66e0059f5684dc Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable > I notice your post puts little spotlight on unilateral cases. > A thing to note, is that we only use `nSequence` and the weird watermark on unilateral closes. > Even HTLCs only exist on unilateral closes --- on mutual closes we wait for HTLCs to settle one way or the other before doing the mutual close. Yes, I'm only aiming LN-cooperative cases, as your noticed HTLCs only exist on commitment txn and masquerading them in some Taptree would come with its own challenges. Cooperative closings should be the majority of channels if network is reliable and so would be a set big enough to achieve the goal of blurring Coinjoins among LN transactions. Right now we don't use `nSequence` but the current interactive tx construction proposal uses it for RBF (weird watermark was an example). > On mutual closes, we should probably set `nLockTime` to the current blockheight + 1 as well. > This has greater benefit later in a Taproot world. I assume mutual closes would fall under the aforementioned tx construction proposal, so a closing may be a batch to fund other channels or splice existent ones. > A kind of non-equal-value CoinJoin could emulate a Lightning open + close, but most Lightning channels will have a large number of blocks (thousands or tens of thousands) between the open and the close; it seems unlikely that a short-term channel will exist > that matches the non-equal-value CoinJoin. That's a really acute point, utxo age and spending frequency may be obvious protocol leaks. Splicing may help there because a LN node would do multiple chain writes during channel lifecycle for liquidity reasons but it's near-impossible to predict its frequency without deployment. Even with this, I do fear an analysis gap between Coinjoin spending delta and LN ones. A way to circumvent this would be for CoinjoinXT to timelock its PTG transactions to mimick actively-spliced LN channels. That's where adoption of a common format by other onchain transactions than LN ones would help a lot. > Should always be on, even if we do not (yet) have a facility to re-interact to bump fees higher. > While it is true that a surveillor can determine that a transaction has in fact been replaced (by observing the mempool) and thus eliminate the set of transactions that arose from protocols that mark RBF but do not (yet) have a facility to bump fees higher, this > information is not permanently recorded on all fullnodes and at least we force surveillors to record this information themselves. Yes but if you do this for Core and given some merchants are refusing RBF transactions for onchain payments, people are going to complain... Also see footnote on spurious-RBF about not-having facility to bump fees higher (you can sign multiple RBF transactions in 1-RTT and agree to broadcast them later to obfuscate mempool analysis). > However, it seems to me that we need to as well nail down the details of this format. Of course, just curious of people opinions right now but if it's a good way to solve the described problem, will draft a spec. Le sam. 22 f=C3=A9vr. 2020 =C3=A0 20:29, ZmnSCPxj = a =C3=A9crit : > Ggood morning Antoine, and list, > > > > * nLocktime/nSequence > > ... > > * weird watermark (LN commitment tx obfuscated commitment number) > > ... > > LN (cooperative case): > > I notice your post puts little spotlight on unilateral cases. > A thing to note, is that we only use `nSequence` and the weird watermark > on unilateral closes. > Even HTLCs only exist on unilateral closes --- on mutual closes we wait > for HTLCs to settle one way or the other before doing the mutual close. > > If we assume that unilateral closes are rare, then it might be an > acceptable risk to lose privacy in that case. > Of course, it takes two to tango, and it takes two to make a Lightning > channel, so --- > In any case, I explored some of the difficulties with unilateral closes a= s > well: > > * > https://lists.linuxfoundation.org/pipermail/lightning-dev/2020-January/00= 2421.html > * > https://lists.linuxfoundation.org/pipermail/lightning-dev/2020-January/00= 2415.html > > On mutual closes, we should probably set `nLockTime` to the current > blockheight + 1 as well. > This has greater benefit later in a Taproot world. > > > Questions: > > * Are there any protocol-specific semantic wrt to onchain transactions > incompatibility > > between Coinjoin and cooperative LN txn ? > > A kind of non-equal-value CoinJoin could emulate a Lightning open + close= , > but most Lightning channels will have a large number of blocks (thousands > or tens of thousands) between the open and the close; it seems unlikely > that a short-term channel will exist that matches the non-equal-value > CoinJoin. > > In particular, a LN cooperative close will, in general, have only one > input. > A new form of CoinJoin could, instead of using a single transaction, use > two, with an entry transaction that spends into an n-of-n of the > participants, and the n-of-n being spent to split the coin back to their > owners. > But again: a Lightning network channel would have much time with the fund= s > in a single UTXO before later splitting the funds, > This also starts edging closer to CoinJoinXT territory. > > > * What about RBF-by-default ? > > Should always be on, even if we do not (yet) have a facility to > re-interact to bump fees higher. > While it is true that a surveillor can determine that a transaction has i= n > fact been replaced (by observing the mempool) and thus eliminate the set = of > transactions that arose from protocols that mark RBF but do not (yet) hav= e > a facility to bump fees higher, this information is not permanently > recorded on all fullnodes and at least we force surveillors to record thi= s > information themselves. > > > * Core wallet or any other protocol or even batching algorithms could > adopt > > to this format ? > > It seems likely. > However, it seems to me that we need to as well nail down the details of > this format. > > > * Is artificially increasing the number of outputs to mimic Coinjoins t= xn > > acceptable wrt to utxo bloat/fees ? > > That is indeed an issue. > > Regards, > ZmnSCPxj > --0000000000009e66e0059f5684dc Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
> I notice your post puts litt= le spotlight on unilateral cases.
> A thing to note, is that we only use `nSequence` and the weird waterma= rk on unilateral closes.
> Even HTLCs only exist on unilateral closes --- on mutual closes we wai= t=20 for HTLCs to settle one way or the other before doing the mutual close.
=
Yes, I'm only aiming LN-cooperative cases, as your noticed HT= LCs only exist on commitment txn and masquerading them in some Taptree woul= d come
with its own challenges. Cooperative closings should be the= majority of channels if network is reliable and so would be a set big enou= gh to achieve the goal
of blurring Coinjoins among LN transac= tions.

Right now we don't use `nSequence` but the current inter= active tx construction proposal uses it for RBF (weird watermark was an exa= mple).

> On mutual closes, we should probably set `nLockTim= e` to the current blockheight + 1 as well.
> This has greater benefit later in a Taproot world.

I assume mutual closes would fall under the afore= mentioned tx construction proposal, so a closing may be a batch to fund oth= er channels or
splice existent ones.

> A kind of non-equ= al-value CoinJoin could emulate a Lightning open +=20 close, but most Lightning channels will have a large number of blocks=20 (thousands or tens of thousands) between the open and the close; it=20 seems unlikely that a short-term channel will exist > that matches the= =20 non-equal-value CoinJoin.

That's a really acute point= , utxo age and spending frequency may be obvious protocol leaks. Splicing m= ay help there because a LN node would do multiple chain writes during chann= el lifecycle for liquidity reasons but it's
near-impossible t= o predict its frequency without deployment. Even with this, I do fear an an= alysis gap between Coinjoin spending delta and LN ones. A way to circumvent= this would be for CoinjoinXT to timelock its PTG
transaction= s to mimick actively-spliced LN channels. That's where adoption of a co= mmon format by other onchain transactions than LN ones would help a lot.
> Should always be on, even if we do not (yet) have a facility to r= e-interact to bump fees higher.
> While it is true that a surveillor can determine that a transaction ha= s=20 in fact been replaced (by observing the mempool) and thus eliminate the=20 set of transactions that arose from protocols that mark RBF but do not=20 (yet) have a facility to bump fees higher, this > information is not=20 permanently recorded on all fullnodes and at least we force surveillors=20 to record this information themselves.

Yes but if you do this for Core and = given some merchants are refusing RBF transactions for onchain payments, pe= ople are going to complain...
Also see footnote on spurious-RBF about not-having facility to bump fees h= igher (you can sign multiple RBF transactions in 1-RTT and agree to broadca= st them later to obfuscate mempool analysis).

> However, i= t seems to me that we need to as well nail down the details of this format.=

Of course, just curious of people opinions right now but if it's a goo= d way to solve the described problem, will draft a spec.

Le=C2=A0sam. 22 f=C3=A9vr. 2020 =C3=A0=C2=A020:29, ZmnSCPxj <<= a href=3D"mailto:ZmnSCPxj@protonmail.com">ZmnSCPxj@protonmail.com> a= =C3=A9crit=C2=A0:
Ggood morning Antoine, and list,


> * nLocktime/nSequence
> ...
> * weird watermark (LN commitment tx obfuscated commitment number)
> ...
> LN (cooperative case):

I notice your post puts little spotlight on unilateral cases.
A thing to note, is that we only use `nSequence` and the weird watermark on= unilateral closes.
Even HTLCs only exist on unilateral closes --- on mutual closes we wait for= HTLCs to settle one way or the other before doing the mutual close.

If we assume that unilateral closes are rare, then it might be an acceptabl= e risk to lose privacy in that case.
Of course, it takes two to tango, and it takes two to make a Lightning chan= nel, so ---
In any case, I explored some of the difficulties with unilateral closes as = well:

* https://lists.li= nuxfoundation.org/pipermail/lightning-dev/2020-January/002421.html
* https://lists.li= nuxfoundation.org/pipermail/lightning-dev/2020-January/002415.html

On mutual closes, we should probably set `nLockTime` to the current blockhe= ight + 1 as well.
This has greater benefit later in a Taproot world.

> Questions:
> * Are there any protocol-specific semantic wrt to onchain transactions= incompatibility
> between Coinjoin and cooperative LN txn ?

A kind of non-equal-value CoinJoin could emulate a Lightning open + close, = but most Lightning channels will have a large number of blocks (thousands o= r tens of thousands) between the open and the close; it seems unlikely that= a short-term channel will exist that matches the non-equal-value CoinJoin.=

In particular, a LN cooperative close will, in general, have only one input= .
A new form of CoinJoin could, instead of using a single transaction, use tw= o, with an entry transaction that spends into an n-of-n of the participants= , and the n-of-n being spent to split the coin back to their owners.
But again: a Lightning network channel would have much time with the funds = in a single UTXO before later splitting the funds,
This also starts edging closer to CoinJoinXT territory.

> * What about RBF-by-default ?

Should always be on, even if we do not (yet) have a facility to re-interact= to bump fees higher.
While it is true that a surveillor can determine that a transaction has in = fact been replaced (by observing the mempool) and thus eliminate the set of= transactions that arose from protocols that mark RBF but do not (yet) have= a facility to bump fees higher, this information is not permanently record= ed on all fullnodes and at least we force surveillors to record this inform= ation themselves.

> * Core wallet or any other protocol or even batching algorithms could = adopt
> to this format ?

It seems likely.
However, it seems to me that we need to as well nail down the details of th= is format.

> * Is artificially increasing the number of outputs to mimic Coinjoins = txn
> acceptable wrt to utxo bloat/fees ?

That is indeed an issue.

Regards,
ZmnSCPxj
--0000000000009e66e0059f5684dc--