From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 09702C07FF for ; Sat, 4 Apr 2020 12:07:38 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id EE92587C74 for ; Sat, 4 Apr 2020 12:07:37 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ppyM5UkcbcJK for ; Sat, 4 Apr 2020 12:07:35 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-40132.protonmail.ch (mail-40132.protonmail.ch [185.70.40.132]) by whitealder.osuosl.org (Postfix) with ESMTPS id 67E1387C5C for ; Sat, 4 Apr 2020 12:07:35 +0000 (UTC) Date: Sat, 04 Apr 2020 12:07:28 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=default; t=1586002052; bh=7d8ym44ss9L0fpOPRMFeAbX1AsDs054B/ZX6iy/Xd/8=; h=Date:To:From:Cc:Reply-To:Subject:In-Reply-To:References:From; b=Uy89TeyTBLU2Ou5w80lODmk7IIJuKi+rq6H9KgIGOUCrZ4AdRxy3+hq7u7f7HrGc4 Q/X6l4ujMRp3b8v0H+YLvaWPGxZk25SzQipaYIv3zO2sebQ+a6tiz5hxQt4VIHiOFA F+J+P4UYi4MNEJgTk7PvbR1POhG+Tn+UywPFcgUQ= To: Nadav Kohen , Bitcoin Protocol Discussion From: ZmnSCPxj Reply-To: ZmnSCPxj Message-ID: In-Reply-To: References: <20200331103508.asvxujkhtifj6n7i@ganymede> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: Tom Trevethan Subject: Re: [bitcoin-dev] Statechain implementations 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: Sat, 04 Apr 2020 12:07:38 -0000 Good morning Nadav, Indeed. It seems to me that practical deployments of statechains requires the state= chain operator to be a trusted federation, possibly a k-of-n. This is slightly better than a federated sidechain because the money can al= ways be reclaimed on the blockchain layer very quickly in case of a loss of= trust in the federation. If the k-of-n is arranged in such a way that the signers can be identified = (such as by use of old `OP_CHECKMULTISIG` or some combination of the propos= ed `OP_CHECKSIGADD`) then it has the same "auditability", i.e. you can iden= tify the pseudonyms of the members who cheated (which is not worth much, as= getting a new pseudonym is trivial). It is helpful to remember that a k-of-n federation can only be trusted if y= ou have full trust in at least (n - k + 1) members of the federation. Regards, ZmnSCPxj > Hey all, > > So my main concern with the proposal as written is that the Statechain En= tity (SE) can untraceably=C2=A0scam its users with the following attack: > 1) Buy the utxo (have it transferred to a key it knows), this first step = can be skipped if the utxo was created by the SE. > 2) Transfer the UTXO to someone else, let it be for however long > 3) When it wishes to steal the UTXO, the SE now knows its own shard s_n a= nd it=C2=A0 knows the full private key, x, from when it owned the UTXO (and= had both shards), and so it can compute x/s_n =3D the current users shard.= It can then sign for the current user, and forge a state transition to a k= ey it owns before spending the UTXO on chain. > > The main problem here is that the user who had their funds stolen cannot = prove to anyone that this has happened since the attack compromises their k= ey. > That said, I think this problem is easily fixed by adding a new user key = to the protocol with which they must sign in order for the transfer to be c= onsidered valid on the state chain. This way, if the SE wishes to steal the= funds (which they still can), at least it is traceable/provable that this = SE is not trustworthy as there is no evidence of a valid transfer for the f= unds that have been stolen. > > Best, > Nadav > > On Thu, Apr 2, 2020 at 7:22 PM Tom Trevethan via bitcoin-dev wrote: > > > Thanks for all of the input and comments - I do now think that the decr= ementing nSequence relative locktime backup system with kick-off transactio= n is the way to go, including a fee penalty via CPFP to disincentivise= =C2=A0DoS, as suggested.=C2=A0 > > I have started a more detailed document specifying the proposed protoco= l in more detail:=C2=A0https://github.com/commerceblock/mercury/blob/master= /statechains.md=C2=A0which includes improvements to the transfer=C2=A0mecha= nism (and an explanation of how this can be used to transfer/novate positio= ns in DLCs). Always happy to get more feedback or PRs.=C2=A0 > > > > Tom > > > > On Tue, Mar 31, 2020 at 12:41 PM Tom Trevethan = wrote: > > > > > Hi David, > > > > > > Just for clarity, I left nChain over 2 years ago (having worked there= since 2016). While there, I (along with other researchers) were given free= rein to work on any ideas we wanted to. I had been interested in the scali= ng of Bitcoin off-chain, and this was one of several things I spent time on= (including things like sidechains,=C2=A0pegs and threshold signatures). Th= is patent application came out of an idea I had to transfer ownership of UT= XOs off-chain that has some similarities to the statechains proposal, which= has shown there is interest and demand for this type of system.=C2=A0 > > > > > > Although I think the existence of this application is something to be= mindful of, there are several important things to note: > > > > > > 1. Although there are similarities, the current ideas are significant= ly different to those in the application.=C2=A0 > > > 2. The key transfer protocol as described in the application is not s= ecure (for several reasons, including as discussed above, by Albert and Bob= etc.) - and a different mechanism is required.=C2=A0 > > > 3. Decrementing timelocks (as suggested in the application) are prior= art (Decker-Wattenhofer 2015), and in any case any implementation will mos= t likely use an 'invalidation tree' relative locktime backup mechanism for = open-ended UTXOs.=C2=A0 > > > 4. The patent application has not been granted (it was made in May 20= 17) and the international search report rejected it on the grounds of prior= art.=C2=A0 > > > > > > Tom > > > > > > On Tue, Mar 31, 2020 at 11:36 AM David A. Harding wro= te: > > > > > > > On Wed, Mar 25, 2020 at 01:52:10PM +0000, Tom Trevethan via bitcoin= -dev wrote: > > > > > Hi all, > > > > > > > > > > We are starting to work on an implementation of the statechains c= oncept ( > > > > > https://medium.com/@RubenSomsen/statechains-non-custodial-off-cha= in-bitcoin-transfer-1ae4845a4a39), > > > > > > > > > > [...] > > > > > There are two main modifications we are looking at: > > > > > [...] > > > > > > > > > > 2. Replacing the 2-of-2 multisig output (paying to statechain ent= ity SE key > > > > > and transitory key) with a single P2(W)PKH output where the publi= c key > > > > > shared between the SE and the current owner. The SE and the curre= nt owner > > > > > can then sign with a 2-of-2 ECDSA MPC. > > > > > > > > Dr. Trevethan, > > > > > > > > Would you be able to explain how your proposal to use statechains w= ith > > > > 2P-ECDSA relates to your patent assigned to nChain Holdings for "Se= cure > > > > off-chain blockchain transactions"?[1]=C2=A0 > > > > > > > > =C2=A0 =C2=A0 [1] https://patents.google.com/patent/US20200074464A1 > > > > > > > > Here are some excerpts from the application that caught my attentio= n in > > > > the context of statechains in general and your proposal to this lis= t in > > > > particular: > > > > > > > > > an exchange platform that is trusted to implement and operate the > > > > > transaction protocol, without requiring an on-chain transaction. = The > > > > > off-chain transactions enable one computer system to generate mul= tiple > > > > > transactions that are recordable to a blockchain in different > > > > > circumstances > > > > > > > > > > [...] > > > > > > > > > > at least some of the off-chain transactions are valid for recordi= ng on > > > > > the blockchain even in the event of a catastrophic failure of the > > > > > exchange (e.g., exchange going permanently off-line or loosing ke= y > > > > > shares). > > > > > > > > > > [...] > > > > > > > > > > there may be provided a computer readable storage medium includin= g a > > > > > two-party elliptic curve digital signature algorithm (two-party E= CDSA) > > > > > script comprising computer executable instructions which, when > > > > > executed, configure a processor to perform functions of a two-par= ty > > > > > elliptic curve digital signature algorithm described herein. > > > > > > > > > > [...] > > > > > > > > > > In this instance the malicious actor would then also have to coll= ude > > > > > with a previous owner of the funds to recreate the full key. Beca= use > > > > > an attack requires either the simultaneous theft of both exchange= and > > > > > depositor keys or collusion with previous legitimate owners of fu= nds, > > > > > the opportunities for a malicious attacker to compromise the exch= ange > > > > > platform are limited. > > > > > > > > Thank you, > > > > > > > > -Dave > > > > _______________________________________________ > > bitcoin-dev mailing list > > bitcoin-dev@lists.linuxfoundation.org > > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev