Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 363D71434 for ; Mon, 5 Oct 2015 22:03:50 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-ig0-f174.google.com (mail-ig0-f174.google.com [209.85.213.174]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 032D5E4 for ; Mon, 5 Oct 2015 22:03:48 +0000 (UTC) Received: by igcrk20 with SMTP id rk20so71793293igc.1 for ; Mon, 05 Oct 2015 15:03:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=kRmFtJWHusJfjMXZ+5uPcqVfOSvQYfvzW+gdsnp+Yoc=; b=IMaJIaSCVFEcS2LKE7i00u/NpiU6omtR/tkd87A3DiCllZHZ0oIhItsIGU33XQWAKS 7NPNngZb2bkErdNb+Wttj+soUFc2Nfa7HTq7obrbsJKEnznc5fwBrbyt29wd07gmrAkQ koc4BAeqfUPrC4BItX4/SqACwRcbrrY4dUsaxg3CiK+tXlYyBQNh5j7pOFMAlSOTnnR6 Yh0j3qQ54e9/5s31Ev+mFOMu702ctNrdPco9bPKDPuCMQ29wo0KU9gkmWVBAzPduJ34T EeLrl76N3CgOfBeHElUddx5Ga/pbuhdFI4vTS8QmB2YcUyCYQmXHpwcqwlGFzrs2iCAl A+Vw== MIME-Version: 1.0 X-Received: by 10.50.30.101 with SMTP id r5mr7524394igh.35.1444082628343; Mon, 05 Oct 2015 15:03:48 -0700 (PDT) Received: by 10.64.106.103 with HTTP; Mon, 5 Oct 2015 15:03:48 -0700 (PDT) In-Reply-To: <561115C0.3080601@sky-ip.org> References: <20151003143056.GA27942@muck> <20151004083525.GA18291@navy> <561115C0.3080601@sky-ip.org> Date: Mon, 5 Oct 2015 18:03:48 -0400 Message-ID: From: Alex Morcos To: s7r@sky-ip.org Content-Type: multipart/alternative; boundary=047d7bdca97e16d140052162b027 X-Spam-Status: No, score=-2.7 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,HTML_MESSAGE,RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: Bitcoin Dev , Anthony Towns Subject: Re: [bitcoin-dev] CHECKSEQUENCEVERIFY - We need more usecases to motivate the change X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Development Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 05 Oct 2015 22:03:50 -0000 --047d7bdca97e16d140052162b027 Content-Type: text/plain; charset=UTF-8 Peter, Your concern about whether this is the best way to use the nSequence field; would that be addressed by providing more high order bits to signal different uses of the field? At a certain point we're really not limiting the future at all and there is something to be said for not letting the perfect be the enemy of the good. I think it would be nice to make forward progress on BIPS 68,112, and 113 and move towards getting them finalized and implemented. (Although I do suspect they aren't quite ready to go out with CLTV) What is the reasoning for having single second resolution on the time based sequence number locks? Might it not make some sense to reduce that resolution and leave more low order bits as well? Alex On Sun, Oct 4, 2015 at 8:04 AM, s7r via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA256 > > Hi aj, > > On 10/4/2015 11:35 AM, Anthony Towns via bitcoin-dev wrote: > > On Sat, Oct 03, 2015 at 04:30:56PM +0200, Peter Todd via > > bitcoin-dev wrote: > >> So we need to make the case for two main things: 1) We have > >> applications that need a relative (instead of absolute CLTV) 2) > >> Additionally to RCLTV, we need to implement this via nSequence > > > >> However I don't think we've done a good job showing why we need > >> to implement this feature via nSequence. BIP68 describes the new > >> nSequence semantics, and gives the rational for them as being a > >> "Consensus-enforced tx replacement" mechanism, with a > >> bidirectional payment channel as an example of this in action. > >> However, the bidirectional payment channel concept itself can be > >> easily implemented with CLTV alone. > > > > Do you mean "with RCLTV alone" here? > > > > RCLTV/OP_CSV is used in lightning commitment transactions to > > enforce a delay between publishing the commitment transaction, and > > spending the output -- that delay is needed so that the > > counterparty has time to prove the commitment was revoked and claim > > the outputs as a penalty. > > > > I partially understand - can you please provide a simple Alice and Bob > example here with the exact scenario? Thanks. Why is there a need to > 'delay between publishing the commitment transaction and spending the > output'? If the absolute CLTV script reached its maturity it means > something went wrong (e.g. counterparty cheated or got hit by a bus) > so what is with the delay time needed for proving that the commitment > was revoked? I assume an absolute CLTV script reaching its maturity > (nLockTime) is the proof itself that the commitment was revoked - but > maybe I'm missing something obvious, sorry if this is the case. > > > Using absolute CLTV instead would mean that once the effective > > delay a commitment transaction has decreases over time -- initially > > it will be longer than desirable, causing unwanted delays in > > claiming funds when no cheating is going on; but over time it will > > become too short, which means there is not enough time to prove > > cheating (and the channel has to be closed prematurely). You can > > trade those things off and pick something that works, but it's > > always going to be bad. > > > I agree, I see the logic here. Absolute CLTV is not necessary inferior > to RCLTV - there are use cases and use cases. For example, you can > avoid unnecessary waiting until the nLockTime expires if you use > absolute CLTV in combination with P2SH (2/2). Again, it always depends > on the use case - it might be a good solution, it might not be such a > good solution, but even absolute CLTV alone clearly fixes a lot of > things and takes smart contracts to the next level. > > >> There is a small drawback in that the initial transaction could > >> be delayed, reducing the overall time the channel exists, but the > >> protocol already assumes that transactions can be reliably > >> confirmed within a day - significantly less than the proposed 30 > >> days duration of the channel. > > > > Compared to using a CLTV with 30 days duration, With RCLTV a > > channel could be available for years (ie 20x longer), but in the > > case of problems funds could be reclaimed within hours or days (ie > > 30x faster). > > > Indeed. I for one _need_ CLTV / RCLTV in my day to day use cases, it > would be neat to have both, but if I can only have (for the time > being) absolute CLTV so be it - it's still a lot better. > > > But that's all about RCLTV vs CLTV, not about RCLTV vs > > nSequence/OP_CSV. ie, it needs BIP 112 (OP_CSV) but not necessarily > > BIP 68 (nSequence relative locktime), if they could be > > disentangled. > > > > You could do all that with " OP_CHECK_HEIGHT_DELTA_VERIFY" that > > ignores nSequence, and directly compares the height of the current > > block versus the input tx's block (or the diff of their > > timestamps?) though, I think? > > > > I think the disadvantage is that (a) you have to look into the > > input transaction's block height when processing the script; and > > (b) you don't have an easy lookup to check whether the transaction > > can be included in the next block. > > > > You could maybe avoid (b) by using locktime though. Have " > > OP_CHECK_RELATIVE_LOCKTIME_VERIFY" compare the transactions > > locktime against the input's block height or time; if the locktime > > is 0 or too low, the transaction is invalid. (So if nLockTime is in > > blockheight, you can only spend inputs with blockheight based > > OP_CRLTV tests; and if it's in blocktime, you can only spend inputs > > with blocktime based OP_CRLTV. "n" does need to encode whether it's > > time/block height though). > > > > That way, when you see a txn: > > > > - run the script. if you see RCLTV, then + if the tx's locktime > > isn't set, it's invalid; drop it + if the input txn is unconfirmed, > > it's invalid; try again later + workout "locktime - n" if that's >= > > the input tx's block height/time, it's good; keep it in mempool, > > forward it, etc > > > > - if you're mining, include the tx when locktime hits, just like > > you would any other valid tx with a locktime > > > > I think the use cases for BIP68 (nSequence) are of the form: > > > > 1) published input; here's a signed tx that spends it to you, > > usable after a delay. might as well just use absolute locktime > > here, though. > > > > 2) here's an unpublished input, you can build your own transaction > > to spend it, just not immediately after it's published. BIP112 is > > required, and OP_RCLTV as defined above works fine, just include > > it in the published input's script. > > > > 3) here's an unpublished input, and a signed transaction spending > > it, that you can use to spend it after a delay. BIP68 is enough; > > but OP_RCLTV in the second transaction works here. however without > > normalised tx ids, the input could be malleated before > > publication, so maybe this use case isn't actually important > > anyway. > > > > So I think OP_CRLTV alone works fine for them too... > > > > (Does that make sense, or am I missing something obvious?) > > > > Cheers, aj > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v2.0.22 (MingW32) > > iQEcBAEBCAAGBQJWERXAAAoJEIN/pSyBJlsRypMH/2Q+jVRf4hWtPr9cs/06pXM9 > mKHd2OPDEJO8HjSe+cIMCxOz76EZxXglUEkK4YV/huP0Tp0bcMp6EJxsZVD9L78k > dugyh2747ddL6aqRmt0ducTEfIC/Q4BxPA2HRQZkvyyIUQv2Tyo780bC0y8BwUpb > j/BQjFZwk4QgqkTlf5lbCgn85alOKHki2El04iALHc27pUiDWKQPPeNOy6po6mmD > /csvh4XOTQwCVy384ljuFBp0+QN7Z/zx4E8i6GqV2BmfNcveTG6Fc5KrHr2Ud4Th > RD8k6n9mLaPs6ufhVkgUiUqPzQsJ+ns+mm7OEUdd645Kxqxg3Tu1u32DgdpRcHk= > =U0N6 > -----END PGP SIGNATURE----- > _______________________________________________ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev > --047d7bdca97e16d140052162b027 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Peter,

Your concern about whether this = is the best way to use the nSequence field; would that be addressed by prov= iding more high order bits to signal different uses of the field?=C2=A0 At = a certain point we're really not limiting the future at all and there i= s something to be said for not letting the perfect be the enemy of the good= .=C2=A0 I think it would be nice to make forward progress on BIPS 68,112, a= nd 113 and move towards getting them finalized and implemented. =C2=A0(Alth= ough I do suspect they aren't quite ready to go out with CLTV)

What is the reasoning for having single second resolution = on the time based sequence number locks?=C2=A0 Might it not make some sense= to reduce that resolution and leave more low order bits as well?

Alex

On Sun, Oct 4, 2015 at 8:04 AM, s7r via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:=
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

Hi aj,

On 10/4/2015 11:35 AM, Anthony Towns via bitcoin-dev wrote:
> On Sat, Oct 03, 2015 at 04:30:56PM +0200, Peter Todd via
> bitcoin-dev wrote:
>> So we need to make the case for two main things: 1) We have
>> applications that need a relative (instead of absolute CLTV) 2) >> Additionally to RCLTV, we need to implement this via nSequence
>
>> However I don't think we've done a good job showing why we= need
>> to implement this feature via nSequence. BIP68 describes the new >> nSequence semantics, and gives the rational for them as being a >> "Consensus-enforced tx replacement" mechanism, with a >> bidirectional payment channel as an example of this in action.
>> However, the bidirectional payment channel concept itself can be >> easily implemented with CLTV alone.
>
> Do you mean "with RCLTV alone" here?
>
> RCLTV/OP_CSV is used in lightning commitment transactions to
> enforce a delay between publishing the commitment transaction, and
> spending the output -- that delay is needed so that the
> counterparty has time to prove the commitment was revoked and claim > the outputs as a penalty.
>

I partially understand - can you please provide a simple Alice and B= ob
example here with the exact scenario? Thanks. Why is there a need to
'delay between publishing the commitment transaction and spending the output'? If the absolute CLTV script reached its maturity it means
something went wrong (e.g. counterparty cheated or got hit by a bus)
so what is with the delay time needed for proving that the commitment
was revoked? I assume an absolute CLTV script reaching its maturity
(nLockTime) is the proof itself that the commitment was revoked - but
maybe I'm missing something obvious, sorry if this is the case.

> Using absolute CLTV instead would mean that once the effective
> delay a commitment transaction has decreases over time -- initially > it will be longer than desirable, causing unwanted delays in
> claiming funds when no cheating is going on; but over time it will
> become too short, which means there is not enough time to prove
> cheating (and the channel has to be closed prematurely). You can
> trade those things off and pick something that works, but it's
> always going to be bad.
>
I agree, I see the logic here. Absolute CLTV is not necessary inferi= or
to RCLTV - there are use cases and use cases. For example, you can
avoid unnecessary waiting until the nLockTime expires if you use
absolute CLTV in combination with P2SH (2/2). Again, it always depends
on the use case - it might be a good solution, it might not be such a
good solution, but even absolute CLTV alone clearly fixes a lot of
things and takes smart contracts to the next level.

>> There is a small drawback in that the initial transaction could >> be delayed, reducing the overall time the channel exists, but the<= br> >> protocol already assumes that transactions can be reliably
>> confirmed within a day - significantly less than the proposed 30 >> days duration of the channel.
>
> Compared to using a CLTV with 30 days duration, With RCLTV a
> channel could be available for years (ie 20x longer), but in the
> case of problems funds could be reclaimed within hours or days (ie
> 30x faster).
>
Indeed. I for one _need_ CLTV / RCLTV in my day to day use cases, it=
would be neat to have both, but if I can only have (for the time
being) absolute CLTV so be it - it's still a lot better.

> But that's all about RCLTV vs CLTV, not about RCLTV vs
> nSequence/OP_CSV. ie, it needs BIP 112 (OP_CSV) but not necessarily > BIP 68 (nSequence relative locktime), if they could be
> disentangled.
>
> You could do all that with "<n> OP_CHECK_HEIGHT_DELTA_VERIF= Y" that
> ignores nSequence, and directly compares the height of the current
> block versus the input tx's block (or the diff of their
> timestamps?) though, I think?
>
> I think the disadvantage is that (a) you have to look into the
> input transaction's block height when processing the script; and > (b) you don't have an easy lookup to check whether the transaction=
> can be included in the next block.
>
> You could maybe avoid (b) by using locktime though. Have "<n&g= t;
> OP_CHECK_RELATIVE_LOCKTIME_VERIFY" compare the transactions
> locktime against the input's block height or time; if the locktime=
> is 0 or too low, the transaction is invalid. (So if nLockTime is in > blockheight, you can only spend inputs with blockheight based
> OP_CRLTV tests; and if it's in blocktime, you can only spend input= s
> with blocktime based OP_CRLTV. "n" does need to encode wheth= er it's
> time/block height though).
>
> That way, when you see a txn:
>
> - run the script. if you see <n> RCLTV, then + if the tx's l= ocktime
> isn't set, it's invalid; drop it + if the input txn is unconfi= rmed,
> it's invalid; try again later + workout "locktime - n" i= f that's >=3D
> the input tx's block height/time, it's good; keep it in mempoo= l,
> forward it, etc
>
> - if you're mining, include the tx when locktime hits, just like > you would any other valid tx with a locktime
>
> I think the use cases for BIP68 (nSequence) are of the form:
>
> 1) published input; here's a signed tx that spends it to you,
> usable after a delay. might as well just use absolute locktime
> here, though.
>
> 2) here's an unpublished input, you can build your own transaction=
> to spend it, just not immediately after it's published. BIP112 is<= br> > required, and OP_RCLTV as defined above works fine, just include
> it in the published input's script.
>
> 3) here's an unpublished input, and a signed transaction spending<= br> > it, that you can use to spend it after a delay. BIP68 is enough;
> but OP_RCLTV in the second transaction works here. however without
> normalised tx ids, the input could be malleated before
> publication, so maybe this use case isn't actually important
> anyway.
>
> So I think OP_CRLTV alone works fine for them too...
>
> (Does that make sense, or am I missing something obvious?)
>
> Cheers, aj
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