From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 480DBBE4 for ; Mon, 9 Sep 2019 04:14:17 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-40133.protonmail.ch (mail-40133.protonmail.ch [185.70.40.133]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id C058D6D6 for ; Mon, 9 Sep 2019 04:14:15 +0000 (UTC) Date: Mon, 09 Sep 2019 04:14:07 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=default; t=1568002452; bh=SLZZp1tC0Ua8GgW8/GsV0bSuzEDcPtFzqk1K1GlyCFU=; h=Date:To:From:Reply-To:Subject:In-Reply-To:References:Feedback-ID: From; b=OdcFmZc82QulfJ0qVCJTzefQJohCrk/1R7KmtvapzbfbAde7U24NDVDJUnr0E9VMt PLcnvDZPR/12Vuk0dZYZF7ZSaRNSoSfctWaboVpVwXl4+O9crw6taX9xq8dQZko6XW zcBRTa8ZTEQyE/uzN79iZInG+iohKbQz2QayvFO8= To: Ruben Somsen , Bitcoin Protocol Discussion From: ZmnSCPxj Reply-To: ZmnSCPxj Message-ID: In-Reply-To: References: Feedback-ID: el4j0RWPRERue64lIQeq9Y2FP-mdB86tFqjmrJyEPR9VAtMovPEo9tvgA0CrTsSHJeeyPXqnoAu6DN-R04uJUg==:Ext:ProtonMail MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-2.2 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, FREEMAIL_FROM, FROM_LOCAL_NOVOWEL, 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 Subject: Re: [bitcoin-dev] PoW fraud proofs without a soft fork X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 09 Sep 2019 04:14:17 -0000 Good morning Ruben, > One might intuitively feel that the lack of a commitment is unsafe, > but there seems to be no impact on security (only bandwidth). The onl= y > way you can be fooled is if all peers lie to you (Sybil), causing you > to follow a malicious minority chain. But even full nodes (or the > committed version of PoW fraud proofs) can be fooled in this way if > they are denied access to the valid most PoW chain. If there are > additional security concerns I overlooked, I=E2=80=99d love to hear t= hem. I think it would be better to more precisely say that: 1. In event of a sybil attack, a fullnode will stall and think the blockch= ain has no more miners. 2. In event of a sybil attack, an SPV, even using this style, will follow = the false blockchain. This has some differences when considering automated systems. Onchain automated payment processing systems, which use a fullnode, will re= fuse to acknowledge any incoming payments. This will lead to noisy complaints from clients of the automated payment pr= ocessor, but this is a good thing since it warns the automated payment proc= essor of the possibility of this attack occurring on them. The use of a timeout wherein if the fullnode is unable to see a new block f= or, say, 6 hours, could be done, to warn higher-layer management systems to= pay attention. While it is sometimes the case that the real network will be unable to find= a new block for hours at a time, this warning can be used to confirm if su= ch an event is occurring, rather than a sybil attack targeting that fullnod= e. On the other hand, such a payment processing system, which uses an SPV with= PoW fraud proofs, will be able to at least see incoming payments, and cont= inue to release product in exchange for payment. Yet this is precisely a point of attack, where the automated payment proces= sing system is sybilled and then false payments are given to the payment pr= ocessor on the attack chain, which are double-spent on the global consensus= chain. And the automated system may very well not be able to notice this. Regards, ZmnSCPxj