Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id DCE6C1D81 for ; Tue, 6 Oct 2015 00:19:28 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-ig0-f169.google.com (mail-ig0-f169.google.com [209.85.213.169]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 9F29A79 for ; Tue, 6 Oct 2015 00:19:26 +0000 (UTC) Received: by igcpb10 with SMTP id pb10so75714239igc.1 for ; Mon, 05 Oct 2015 17:19:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-type; bh=TWP3LAsMkx2mo0mcv0cOVbgPN7ecIG5VLAoxKwUSZlE=; b=FUqC06Vt6W/PkIUBX5EWTbq5+GOngsnEaKaijq+HYY1SUPRqtkTFkT2txIyr+f5pnZ HgunSHUqtHmZfPBzFXpvHJJhfXFTu6Ce7UgqPdfnAC1ZNlOCSsQQJGwKKK94ENAPaWrM KSE4Yo/akRrOlbxt14+jfLAPATskWumWoYQeKNkPmW3HTchQWGT8U7ks2C4y94Se2Acv HGMJBJzk/6CzRuvtr6nN+nanmYD885eOL4xHepvaQ+FR1/GI4eD0RKg2NOM0zB24Wk58 VC4Zy376qjjixKnR/tTCc821ZvVyWg9PqlI10BjobKnaV2xIGs5TbjTSQ51Ppet7DLJQ bM+Q== X-Gm-Message-State: ALoCoQmijq/ufgivKxpskP6OHVbTv57zZkKxWnhUU6D/6sMPilQSpVPtYS6Cd11XLlN/sBfS3Uqe X-Received: by 10.50.30.39 with SMTP id p7mr12682133igh.40.1444090766085; Mon, 05 Oct 2015 17:19:26 -0700 (PDT) MIME-Version: 1.0 Received: by 10.107.135.104 with HTTP; Mon, 5 Oct 2015 17:19:06 -0700 (PDT) X-Originating-IP: [173.228.107.141] In-Reply-To: References: <20151003143056.GA27942@muck> <20151004083525.GA18291@navy> <561115C0.3080601@sky-ip.org> From: Mark Friedenbach Date: Mon, 5 Oct 2015 17:19:06 -0700 Message-ID: To: Alex Morcos Content-Type: multipart/alternative; boundary=047d7bdca5c02307360521649522 X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,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: Tue, 06 Oct 2015 00:19:29 -0000 --047d7bdca5c02307360521649522 Content-Type: text/plain; charset=UTF-8 Alex, decreasing granularity is a soft-fork, increasing is a hard-fork. Therefore I've kept the highest possible precision (1 second, 1 block) with the expectation that at some point in the future if we need more low-order bits we can soft-fork them to other purposes, we can decrease granularity at that time. On Mon, Oct 5, 2015 at 3:03 PM, Alex Morcos via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > 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 >> > > > _______________________________________________ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev > > --047d7bdca5c02307360521649522 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Alex, decreasing granularity is a soft-fork, increasing is= a hard-fork. Therefore I've kept the highest possible precision (1 sec= ond, 1 block) with the expectation that at some point in the future if we n= eed more low-order bits we can soft-fork them to other purposes, we can dec= rease granularity at that time.

On Mon, Oct 5, 2015 at 3:03 PM, Alex Morcos via bit= coin-dev <bitcoin-dev@lists.linuxfoundation.org>= ; wrote:
Peter,
Your concern about whether this is the best way to use th= e nSequence field; would that be addressed by providing more high order bit= s to signal different uses of the field?=C2=A0 At a certain point we're= really not limiting the future at all and there is something to be said fo= r 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, and 113 and move towards g= etting them finalized and implemented. =C2=A0(Although I do suspect they ar= en't quite ready to go out with CLTV)

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

Alex
<= br>
On Sun, Oct 4, 2015 at 8:04 AM, s7r via bitco= in-dev <bitcoin-dev@lists.linuxfoundation.org><= /span> wrote:
-----BEGIN PGP SIGNED MESSA= GE-----
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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bitcoin-dev mailing list
= bitcoin-dev@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mail= man/listinfo/bitcoin-dev


_______________________________________________
bitcoin-dev mailing list
bitcoin-dev@lists.= linuxfoundation.org
https://lists.linuxfoundation.org/mail= man/listinfo/bitcoin-dev


--047d7bdca5c02307360521649522--