Return-Path: Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id A2CB7C016F for ; Wed, 13 May 2020 19:03:34 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 8ACCB89438 for ; Wed, 13 May 2020 19:03:34 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id T-AwSgbHIITs for ; Wed, 13 May 2020 19:03:31 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-ej1-f48.google.com (mail-ej1-f48.google.com [209.85.218.48]) by hemlock.osuosl.org (Postfix) with ESMTPS id 61208892AC for ; Wed, 13 May 2020 19:03:31 +0000 (UTC) Received: by mail-ej1-f48.google.com with SMTP id e2so422485eje.13 for ; Wed, 13 May 2020 12:03:31 -0700 (PDT) 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=ByJxDnKZi4TtjZZKEld0PhoezZYTxk1pEna+TkZ+irc=; b=oZGUcxRyqID0wOTkNf3r3VqyJPr/PFk0RxCmN5L5avLATh8ysBHwuqSbvEPuH4CIWy QA/aZGAofdn+VvBS/b3UGzE2f34UN065DzLFkCA27MeNSIt0awC7LWhoSvFmJteBXJuu bv8ImdnF7m87i6GLPUBsD0pV8EvEjF95mXQuJhrAYwHEa0PusGzWNqhZvFq44uXXr/gm 0QwHxaEGXiqrCeMHWiCbQaNd9yZQV/nFsfPJGCgAZgLFHk8xdScNNVlkifiZQN4LeXBU McuSnltvIC1k73xoqr8ljvDt8fkfEzWb4Xvl0PwDfMUKXnYQkhOUbSfG6k+p5sGunnev aayQ== 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=ByJxDnKZi4TtjZZKEld0PhoezZYTxk1pEna+TkZ+irc=; b=DEAlWQ34+7tkKcT+kPu8qXuj7RXxgJE6rhbdIWpSRqkHMZUkK/VFmn+sNXPxfDqyhB /Qntirx2dMWcy8trHfIxw9vyHk/DyX11POxYE7dWJR117v2foG7sH0iDbGGsXySMJVCM KezMyLTz93/uhb0SYOVkD+2d2LpmhoEznmoOspIL16zvnsx53AL3yTBLvaqOmSayE1hD vtHmjhTaeTN94WiZ9oYtO/9XFbx2z0LbYzrRMwol9fEHq5rySbObw9fmVQLawKo8pVgl m8kd+sfT1j1xmRQ9i9/PxREo9iAqZB8IG4r9RdiDBuvPO+cp2LP7UYaQ3CNrRHVmVzLP F62Q== X-Gm-Message-State: AOAM5324EJfHcL8pI1wyjjyT3wllHQ7vhDKLTC9uXlYogCwXPhtAqQ44 F7hwnNLQayvh5osm3mxsyMvawKlpGXuqBGKQCmXNzM+V X-Google-Smtp-Source: ABdhPJzeJmURk8E5vlxYa+1NX0qapLtaKxCxbjH4MtI+IlUPnSZOz0m55Cww0DlwxQ/n62gDa22RoHuK9c8/gRmgc5s= X-Received: by 2002:a17:906:7f0d:: with SMTP id d13mr465780ejr.312.1589396609615; Wed, 13 May 2020 12:03:29 -0700 (PDT) MIME-Version: 1.0 References: <20200513220222.24953c0a@simplexum.com> In-Reply-To: <20200513220222.24953c0a@simplexum.com> From: Ruben Somsen Date: Wed, 13 May 2020 21:03:17 +0200 Message-ID: To: Dmitry Petukhov Content-Type: multipart/alternative; boundary="00000000000052cd5705a58c3ccf" X-Mailman-Approved-At: Wed, 13 May 2020 19:06:29 +0000 Cc: Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] TLA+ specification for Succint Atomic Swap 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: Wed, 13 May 2020 19:03:34 -0000 --00000000000052cd5705a58c3ccf Content-Type: text/plain; charset="UTF-8" Hi Dmitry, Thanks for creating a specification for testing, I appreciate the interest! >The checking of the model encoded in the specification can successfully detect the violation of 'no mutual secret knowledge' invariant when one of the participant can bypass mempool and give the transaction directly to the miner (this problem was pointed out by ZmnSCPxj in the original SAS thread [2]) I'm not sure if I follow. The issue ZmnSCPxj described about bypassing the mempool was not a violation. It was merely a "nuisance" strategy that causes Alice to have to abort in three transactions. Also note that I subsequently pointed out in the thread that this strategy does not work, because Alice is supposed to abort sooner than that if Bob still has not locked up any funds. Or perhaps you're referring to the issue ZmnSCPxj pointed out after that, where refund transaction #1 and the success transaction could both become valid at the same time. It would make sense for the test to pick up on that, but I believe that is ultimately also not an issue (see my last reply in the thread). >I did not understand what the destination of Alice&Bob cooperative spend of refund_tx#1 will be This transaction can be spent by Alice & Bob right away or by Alice a day later (in relative time, so the tx has to confirm first). The Alice & Bob condition is there purely to ensure that Bob can spend the money before Alice once he receives her key at the end of the protocol. If it helps, you could model this transaction as two separate transactions instead: txA: 1 day absolute timelock to Alice & Bob (reveals secretAlice), which can then be spent by txB: +1 day relative timelock to Alice This should be functionally equivalent. Also note that the protocol should fully function if refund tx #1 did not exist at all. It merely serves to save block space in certain refund scenarios. >it would be great to have an established framework for modelling of the behavior in Bitcoin-like blockchain networks. In particular, having a model of mempool-related behavior would help to reason about difficult RBF/CPFP issues A laudable goal. Good luck with your efforts. Cheers, Ruben On Wed, May 13, 2020 at 7:07 PM Dmitry Petukhov via bitcoin-dev < bitcoin-dev@lists.linuxfoundation.org> wrote: > The Succint Atomic Swap contract presented by Ruben Somsen recently has > drawn much interest. > > I personally am interested in the smart contracts realizeable in the > UTXO model, and also interested in applying formal methods to the > design and implementation of such contracts. > > I think that having formal specifications for the contracts and to be > able to machine-check the properties of these specifications is very > valuable, as it can uncover the corner cases that might be difficult to > uncover otherwise. > > The SAS contract is complex enough that it may benefit from formal > specification and machine checking. > > I created a specification in TLA+ [1] specification language based on > the explanation and the diagram given by Ruben. > > The checking of the model encoded in the specification can successfully > detect the violation of 'no mutual secret knowledge' invariant when one > of the participant can bypass mempool and give the transaction directly > to the miner (this problem was pointed out by ZmnSCPxj in the original > SAS thread [2]) > > There's one transition that was unclear how to model, though: I did not > understand what the destination of Alice&Bob cooperative spend of > refund_tx#1 will be, so this transition is not modelled. > > I believe there can be more invariants and temporal properties of the > model that can be checked. At the moment the temporal properties > checking does not work, as I didn't master TLA+ enough yet. The safety > invariants checking should work fine, though, but more work needed to > devise and add the invariants. > > In the future, it would be great to have an established framework for > modelling of the behavior in Bitcoin-like blockchain networks. > In particular, having a model of mempool-related behavior would help to > reason about difficult RBF/CPFP issues. The specification I present > models the mempool, but in a simple way, without regards to the fees. > > The specification can be found in this github repository: > https://github.com/dgpv/SASwap_TLAplus_spec > > There could be mistakes or omissions in the specified model, I hope > that public review can help find these. > > It would be great to receive comments, suggestions and corrections, > especially from people experienced in formal methods and TLA+, as this > is only my second finished TLA+ spec and only my third project using > formal methods (I created bitcoin transaction deserialization code in > Ada/SPARK before that [3]). Please use the github issues or off-list > mail to discuss if the matter is not interesting to the general > bitcoin-dev list audience. > > [1] https://lamport.azurewebsites.net/tla/tla.html > > [2] > > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-May/017846.html > > [3] https://github.com/dgpv/spark-bitcoin-transaction-example > _______________________________________________ > bitcoin-dev mailing list > bitcoin-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev > --00000000000052cd5705a58c3ccf Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Hi Dmitry,

Thanks for creating a specif= ication for testing, I appreciate the interest!

&g= t;The checking of the model encoded in the specification can successfully d= etect the violation of 'no mutual secret knowledge' invariant when = one of the participant can bypass mempool and give the transaction directly= to the miner (this problem was pointed out by ZmnSCPxj in the original SAS= thread [2])

I'm not sure if I follow. The iss= ue ZmnSCPxj described about bypassing the mempool was not a violation. It w= as merely a "nuisance" strategy that causes Alice to have to abor= t in three transactions. Also note that I subsequently pointed out in the t= hread that this strategy does not work, because Alice is supposed to abort = sooner than that if Bob still has not locked up any funds.

Or perhaps you're referring to the issue=20 ZmnSCPxj pointed out after that, where refund transaction #1 and the success transa= ction could both become valid at the same time. It would make sense for the= test to pick up on that, but I believe that is ultimately also not an issu= e (see my last reply in the thread).

>I did not= understand what the destination of Alice&Bob cooperative spend of refu= nd_tx#1 will be

This transaction can be spent = by Alice & Bob right away or by Alice a day later (in relative time, so= the tx has to confirm first). The Alice & Bob condition is there purel= y to ensure that Bob can spend the money before Alice once he receives her = key at the end of the protocol.

If it helps, you c= ould model this transaction as two separate transactions instead:
txA: 1 day absolute timelock to Alice & Bob (reveals secretAlice), whi= ch can then be spent by
txB: +1 day relative timelock to Alice

This should be functionally equivalent. Also note th= at the protocol should fully function if refund tx #1 did not exist at all.= It merely serves to save block space in certain refund scenarios.

>it would be great to have an established framework for= modelling of the behavior in Bitcoin-like blockchain networks. In particul= ar, having a model of mempool-related behavior would help to reason about d= ifficult RBF/CPFP issues

A laudable goal. Good= luck with your efforts.

Cheers,
Ruben

On Wed, May 13, 2020 at 7:07 PM Dmitry Petukhov via bitcoin-dev <bitcoin-dev@lists.lin= uxfoundation.org> wrote:
The Succint Atomic Swap contract presented by Ruben Somsen = recently has
drawn much interest.

I personally am interested in the smart contracts realizeable in the
UTXO model, and also interested in applying formal methods to the
design and implementation of such contracts.

I think that having formal specifications for the contracts and to be
able to machine-check the properties of these specifications is very
valuable, as it can uncover the corner cases that might be difficult to
uncover otherwise.

The SAS contract is complex enough that it may benefit from formal
specification and machine checking.

I created a specification in TLA+ [1] specification language based on
the explanation and the diagram given by Ruben.

The checking of the model encoded in the specification can successfully
detect the violation of 'no mutual secret knowledge' invariant when= one
of the participant can bypass mempool and give the transaction directly
to the miner (this problem was pointed out by ZmnSCPxj in the original
SAS thread [2])

There's one transition that was unclear how to model, though: I did not=
understand what the destination of Alice&Bob cooperative spend of
refund_tx#1 will be, so this transition is not modelled.

I believe there can be more invariants and temporal properties of the
model that can be checked. At the moment the temporal properties
checking does not work, as I didn't master TLA+ enough yet. The safety<= br> invariants checking should work fine, though, but more work needed to
devise and add the invariants.

In the future, it would be great to have an established framework for
modelling of the behavior in Bitcoin-like blockchain networks.
In particular, having a model of mempool-related behavior would help to
reason about difficult RBF/CPFP issues. The specification I present
models the mempool, but in a simple way, without regards to the fees.

The specification can be found in this github repository:
https://github.com/dgpv/SASwap_TLAplus_spec

There could be mistakes or omissions in the specified model, I hope
that public review can help find these.

It would be great to receive comments, suggestions and corrections,
especially from people experienced in formal methods and TLA+, as this
is only my second finished TLA+ spec and only my third project using
formal methods (I created bitcoin transaction deserialization code in
Ada/SPARK before that [3]). Please use the github issues or off-list
mail to discuss if the matter is not interesting to the general
bitcoin-dev list audience.

[1] https://lamport.azurewebsites.net/tla/tla.html=

[2]
https://lists.linuxfound= ation.org/pipermail/bitcoin-dev/2020-May/017846.html

[3] https://github.com/dgpv/spark-bitcoin-t= ransaction-example
_______________________________________________
bitcoin-dev mailing list
= bitcoin-dev@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mail= man/listinfo/bitcoin-dev
--00000000000052cd5705a58c3ccf--