Delivery-date: Fri, 19 Jul 2024 11:27:44 -0700 Received: from mail-yb1-f189.google.com ([209.85.219.189]) by mail.fairlystable.org with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from <bitcoindev+bncBCU2P6FJ3EBBBF7A5K2AMGQEYCHJEAA@googlegroups.com>) id 1sUsKV-0007hy-2O for bitcoindev@gnusha.org; Fri, 19 Jul 2024 11:27:44 -0700 Received: by mail-yb1-f189.google.com with SMTP id 3f1490d57ef6-e05e9e4dfbesf4923694276.1 for <bitcoindev@gnusha.org>; Fri, 19 Jul 2024 11:27:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlegroups.com; s=20230601; t=1721413657; x=1722018457; darn=gnusha.org; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:x-original-sender:mime-version :subject:references:in-reply-to:message-id:to:from:date:sender:from :to:cc:subject:date:message-id:reply-to; bh=At36Vbhot8pETgQCkBAipoL+dSaeFcHRDCDEWJnAJ9A=; b=BQZjyNfrCQMnbzNfvaa+iwa6SLp7m8EeIyffmK5ONEmTHSzxcgFrK4l84JytZ8gsGe STFYsZEWfpBzyATvYo9PDPNWqv9onKhzvgtK3YYXyKRJnBWRUDOiafEJTdhsa5i8Nzpq 88YcEYwoGiw0kNMdG+vuFEyFvzB4GZPenHVi7ne1kp3ocsTNS6FfTBsZhfBRiWJxFHTO BQ11709oeesyk+rGGQoayq/q7wcxuaRtsmYc0/PokXy0uPCnBJUniuM6QwTHUOAJXzA3 g52mgfVg7NPtXzeCViTJQ1/kNbbMrZOqlSRb1BuXvAn5J3jl3nTCEtb9L7cUtsaFtprN /Qfw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1721413657; x=1722018457; darn=gnusha.org; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:x-original-sender:mime-version :subject:references:in-reply-to:message-id:to:from:date:from:to:cc :subject:date:message-id:reply-to; bh=At36Vbhot8pETgQCkBAipoL+dSaeFcHRDCDEWJnAJ9A=; b=jDmGsN6l/w6XwbnSoy4c1KJVGTw3Y7ezf/bXM92Ex90KQRwXd60XF40u6MCdIaHk1e Ij3Tw5J41SSAOlv0RCBNr3D4r++9pzEKSvJNzTdVIdkDcvfYVjHEIDD/mlnArYfyY/RL Jpueo/3173yQqgAyE2rJ7OpFrj3KJbQqUhQcVIMSzT03NYAvmkez4MOSqnutgWtGR4Yv Wiv9OTP314XNHIhUcFEM80fySe4jfxgjIBi3tMHR4vmmzb46MZEtKldZgtGfv6pd+Hkk 2zrILESYgyI9bYNXHS8wbQGNtY4cK3z1SmaEWkgn4gXHbbB9YGgy1AcsL/prk1i1csD/ 7n/w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721413657; x=1722018457; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:x-original-sender:mime-version :subject:references:in-reply-to:message-id:to:from:date:x-beenthere :x-gm-message-state:sender:from:to:cc:subject:date:message-id :reply-to; bh=At36Vbhot8pETgQCkBAipoL+dSaeFcHRDCDEWJnAJ9A=; b=UkBQl/5Xs/tONbRxqSoLAidEco6D33zkzL6I0A6bnTPm3mS5fwGqkecxfAyE8g3vW7 WGh6sZCvYK236xw8YFRv2CtJgPSgX1CHqB/hRbyJ69GZ6BeFORg4Hgl2Upg1HwPL6i7m ivzbcbsfEwfoM30150ir28vj9KTD+x/GDxq19Li7X9P/h0XQLQ72+LLl2KgVDUZATS8S BFOcMqW2CJPp0MmkdaOdO6SHaKgt3Vy0XM77/WobT5WD0I9uhCuQE3Lbvq4fz5nPOpvT XrXOCmTFXuqb5b2WyeZ71+pVWAGOlOmNfYI+4YXjt5o/NWRe+iWnMfTjiyWwRgTTK60P oTlA== Sender: bitcoindev@googlegroups.com X-Forwarded-Encrypted: i=1; AJvYcCVbYBIV3EVPGc19HU5eg0h+dp7eQzJ9YrImDWDV/tBicIMq/elhhRCaGsXhjERx9ab2h0iRtudcNY1Fe+Q6OhIEMLpcC1A= X-Gm-Message-State: AOJu0YzC2Kinhv6IkhkFZiI1QcsVnQUMmYS4RV6hORQX9plvZEWizkPQ nwPj8bvOJmL1FHnKYhynE4AOU3YAPGVSOWn3E2i2waJDeR3SorXp X-Google-Smtp-Source: AGHT+IHUrjrLg53yrhRyLxl3zASDofVe/17D0bkefTBeHsutohY7zoOEClAwtHWmJzC7CmvyQEFKpA== X-Received: by 2002:a05:6902:f81:b0:e08:6af2:d5b9 with SMTP id 3f1490d57ef6-e08706adb8amr534628276.49.1721413656710; Fri, 19 Jul 2024 11:27:36 -0700 (PDT) X-BeenThere: bitcoindev@googlegroups.com Received: by 2002:a25:f912:0:b0:e03:6457:383f with SMTP id 3f1490d57ef6-e05fdb408a3ls3363212276.1.-pod-prod-09-us; Fri, 19 Jul 2024 11:27:35 -0700 (PDT) X-Received: by 2002:a25:8b86:0:b0:e03:2f90:e81d with SMTP id 3f1490d57ef6-e0870462b60mr8513276.11.1721413655165; Fri, 19 Jul 2024 11:27:35 -0700 (PDT) Received: by 2002:a05:690c:3104:b0:664:87b6:d9e0 with SMTP id 00721157ae682-66918fcc18bms7b3; Fri, 19 Jul 2024 05:41:07 -0700 (PDT) X-Received: by 2002:a05:6902:1004:b0:e03:2257:98b8 with SMTP id 3f1490d57ef6-e05feb3117bmr100638276.1.1721392866989; Fri, 19 Jul 2024 05:41:06 -0700 (PDT) Date: Fri, 19 Jul 2024 05:41:06 -0700 (PDT) From: /dev /fd0 <alicexbtong@gmail.com> To: Bitcoin Development Mailing List <bitcoindev@googlegroups.com> Message-Id: <18a5e5a2-92b3-4345-853d-5a63b71d848bn@googlegroups.com> In-Reply-To: <Zpk7EYgmlgPP3Y9D@petertodd.org> References: <Zpk7EYgmlgPP3Y9D@petertodd.org> Subject: [bitcoindev] Re: A "Free" Relay Attack Taking Advantage of The Lack of Full-RBF In Core MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_159328_1732340751.1721392866788" X-Original-Sender: alicexbtong@gmail.com Precedence: list Mailing-list: list bitcoindev@googlegroups.com; contact bitcoindev+owners@googlegroups.com List-ID: <bitcoindev.googlegroups.com> X-Google-Group-Id: 786775582512 List-Post: <https://groups.google.com/group/bitcoindev/post>, <mailto:bitcoindev@googlegroups.com> List-Help: <https://groups.google.com/support/>, <mailto:bitcoindev+help@googlegroups.com> List-Archive: <https://groups.google.com/group/bitcoindev List-Subscribe: <https://groups.google.com/group/bitcoindev/subscribe>, <mailto:bitcoindev+subscribe@googlegroups.com> List-Unsubscribe: <mailto:googlegroups-manage+786775582512+unsubscribe@googlegroups.com>, <https://groups.google.com/group/bitcoindev/subscribe> X-Spam-Score: -0.5 (/) ------=_Part_159328_1732340751.1721392866788 Content-Type: multipart/alternative; boundary="----=_Part_159329_1526928484.1721392866788" ------=_Part_159329_1526928484.1721392866788 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Peter, > I didn't get a substantive > response from Bitcoin Core, other than Core closing the my pull-req=20 enabling > full-RBF by default that would fix this specific vulnerability. The last comment in the pull request suggests opening a new pull request to= =20 enable full RBF by default, referencing the one closed due to off-topic=20 comments.=20 > But read on, this is quite an odd case of Core politics, and the story is= =20 not > as simple as Core refusing to fix a vulnerability. It seems that you are the one trying to politicize this issue.=20 /dev/fd0 floppy disk guy On Thursday, July 18, 2024 at 4:04:26=E2=80=AFPM UTC Peter Todd wrote: > # Summary > > This is a public disclosure of a vulnerability that I previously disclose= d=20 > to > the bitcoin-security mailing list. It's an easy vulnerability to fix.=20 > Although > as with other "free" relay attacks I've disclosed, I didn't get a=20 > substantive > response from Bitcoin Core, other than Core closing the my pull-req=20 > enabling > full-RBF by default that would fix this specific vulnerability. > > But read on, this is quite an odd case of Core politics, and the story is= =20 > not > as simple as Core refusing to fix a vulnerability. Also, I've including a= =20 > fun > homework problem at the end: figure out how TRUC/V3 transactions itself= =20 > creates > a "free" relay attack. > > > # Background > > This is just one of a few "free" relay attacks that I have recently=20 > disclosed, > including, but not limited to: > > "A Free-Relay Attack Exploiting RBF Rule #6" - Mar 18th 2024 > https://groups.google.com/g/bitcoindev/c/EJYoeNTPVhg > > "A Free-Relay Attack Exploiting Min-Relay-Fee Differences" - Mar 31st 202= 4 > https://groups.google.com/g/bitcoindev/c/3XqfIOYzXqo > > The term "free relay attack" simply refers to any mechanism where=20 > transaction > data can be broadcast at unusually low cost; the "free" in "free relay" i= s=20 > a > misnomer as all these attacks do in fact have some cost. > > This particular attack isn't significantly different than the other attac= ks > I've disclosed. With one important exception: unlike those other attacks, > fixing this particular attack would be quite easy, by enabling full-rbf b= y > default. So I disclosed it to the bitcoin-security mailing list as a test= :=20 > does > Bitcoin Core actually care about free relay attacks? My hypothesis is tha= t=20 > Core > does not, as they know full well that "free" relay is an unavoidable=20 > problem; > I've received absolutely no feedback from any Bitcoin Core members for th= e > other disclosed attacks, beyond achow using my disclosure of the RBF Rule= =20 > #6 > attack as an excuse to remove me from the bitcoin-security mailing list. > > The fact that Core doesn't actually care about "free" relay attacks is=20 > relevant > to TRUC/V3 Transactions. As per BIP-431: > > "The primary problem with [RBFR proposals] is the potential for free rela= y=20 > and DDoS attacks. > > Removing Rule 3 and 4 in general would allow free relay [27]." > > https://github.com/bitcoin/bips/blob/812907c2b00b92ee31e2b638622a4fe14a42= 8aee/bip-0431.mediawiki#user-content-Alternatives_replace_by_feerate > > I believe the authors of that BIP are fully aware of the fact that "free"= =20 > relay > is an unavoidable problem, making their rational for TRUC/V3 bogus, and= =20 > don't > want to admit that they've wasted a large amount of engineering time on a= =20 > bad > proposal. I will be submitting a pull-req to get BIP-431 corrected, as th= e=20 > many > "free" relay attacks I've disclosed clearly show that claiming RBFR would > "allow" free relay is simply not true. > > Notably, full-RBF is _itself_ a transaction pinning fix for many use-case= s; > part of the TRUC/V3 standard is to force full-RBF behavior for V3=20 > transactions. > So Core closing my full-RF pull-req is doubling down on TRUC/V3 in a seco= nd > way, and TRUC/V3 proponents were the ones who tried to get the full-RBF= =20 > option > removed from Core in the first place. If not for this dumb bit of Core > politics, I'm sure my year-old pull-req to enable full-RBF by default wou= ld > have been merged many months ago, as almost all hashpower has adopted=20 > full-RBF > making objections based on "zeroconf" absurd. > > > # The Attack > > If you're a competent Bitcoin engineer, familiar with how mempools work,= =20 > you've > probably figured it out already based on the title: obviously, if a high > percentage of miners are adopting a policy that Bitcoin Core nodes are=20 > not, you > can cheaply consume transaction relay bandwidth by simply relaying=20 > transations > that miners are rejecting. > > Specifically, do the following: > > 1. Broadcast a small, low-fee-rate, tx A with BIP-125 opt-in disabled. > 2. Broadcast a full-RBF double-spend of A, A2, with a higher fee-rate. > 3. Spend the outputs of A in a large, low fee-rate, transaction B with=20 > BIP-125 > opt-in enabled. ~100% of miners will reject B, as it spends an input not = in > their mempools. However Bitcoin Core nodes will waste bandwidth propagati= ng > B. > 4. (Optional) Double-spend B repeatedly. Again, Bitcoin Core nodes will= =20 > waste > bandwidth propagating Bn's that ~100% of miners are ignoring. > 5. Double-spend A2 to recover your funds and do it all over again (or if= =20 > A2 had > a high enough fee-rate, just wait for it to be mined). > > The cost to relay each B transaction depends on the fee-rate of B. Since > Bitcoin Core defaults to a fairly large mempool, the minimum relay=20 > fee-rate is > typically well below the economic fee-rate required for miners to actuall= y=20 > mine > a transaction; Core accepts transactions that are uneconomical for miners= =20 > to > mine for the forseeable future. > > For example, at the moment typical mempools require transactions to pay a= t > least 1sat/vB, while there are hundreds of MvB worth of transactions payi= ng > 4sat/vB, the minimum economical fee-rate. Thus, transactions paying less= =20 > than > 4sat/VB are extremely unlikely to get mined in the nearish future. > > Concretely, broadcasting B transactions at 1sat/vB, 2sat/vB, and 3sat/vB= =20 > would > have almost zero cost as the probability of those transactions getting=20 > mined is > nearly zero. This is true _regardless_ of what % of miners are mining=20 > full-RBF! > As long as you can get at least one miner to mine the A double-spend, the > attack only costs what it cost to get A mined. > > If B's are broadcast at a higher fee-rate than the minimum economical=20 > fee-rate, > then the % of full-RBF miners matters. For example, if only 99% of miners= =20 > mine > full-RBF, the chance of a B transaction getting mined per block is about= =20 > 1%, so > the amortized cost of broadcasting B is about 1% of whatever total fee th= e > highest fee-rate variant of B pays. > > For an attacker who does not need any B to be broadcast, the cost savings= =20 > to > use of relay bandwidth is approximately the ratio of the difference in si= ze > between B and and A. With a maximum standard transaction size of 100KvB, = or > 400KB serialized size, this ratio is on the order of 5000:1, times the=20 > total > number of B variants broadcast, and the % chance of each B being mined;= =20 > it's a > few orders of magnitude. > > Of course, as mentioned above, this is just one of *many* "free" relay=20 > attacks, > so fixing this particular issue doesn't change much. > > > # Attackers Who Benefit From B Getting Mined > > Some attackers actually need B to get mined. For example, imagine an=20 > exchange > who needs to do large consolidation transactions. They could use this=20 > attack > (and some attacks like it) as a way to goad users and miners into mining > consolidation transactions for them at low cost. In this variant of the= =20 > attack, > the attacker would pad the size of B with consolidation spends that they= =20 > needed > to do anyway. Someone who tried to stop the attack by getting B mined (eg= =20 > via > mempool.space's transaction accellerator) would simply be paying the=20 > attacker's > fees for them. > > Obviously, this strategy is only relevant for B's below the economic=20 > fee-rate. > However, the weaker version of this strategy is to parallize the attack,= =20 > and do > your consolidation with the _A_ double-spends to reduce the # of bytes=20 > used per > full-rbf double-spend. > > > # TRUC/V3 Creates a Free Relay Attack > > I'll leave the details of this as a homework problem. But obviously, the > introduction of TRUC/V3 transactions *itself* creates a free relay attack= =20 > very > similar to the above! Just like full-RBF, not all miners will mine V3 > transactions. So you can do the exact same type of attack by taking=20 > advantage > of this difference in mining policy. > > --=20 > https://petertodd.org 'peter'[:-1]@petertodd.org > --=20 You received this message because you are subscribed to the Google Groups "= Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to bitcoindev+unsubscribe@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/= bitcoindev/18a5e5a2-92b3-4345-853d-5a63b71d848bn%40googlegroups.com. ------=_Part_159329_1526928484.1721392866788 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Peter,<br /><br />>=C2=A0I didn't get a substantive<br />> respons= e from Bitcoin Core, other than Core closing the my pull-req enabling<br />= > full-RBF by default that would fix this specific vulnerability.<br /><= br /> The last comment in the pull request suggests opening a new pull request to= enable full RBF by default, referencing the one closed due to off-topic co= mments. <div><br /></div><div>>=C2=A0But read on, this is quite an odd case of C= ore politics, and the story is not<br />> as simple as Core refusing to = fix a vulnerability.</div><div><br /></div><div> It seems that you are the one trying to politicize this issue. </div><div><br /></div><div>/dev/fd0</div><div>floppy disk guy<br /><br /><= /div><div class=3D"gmail_quote"><div dir=3D"auto" class=3D"gmail_attr">On T= hursday, July 18, 2024 at 4:04:26=E2=80=AFPM UTC Peter Todd wrote:<br/></di= v><blockquote class=3D"gmail_quote" style=3D"margin: 0 0 0 0.8ex; border-le= ft: 1px solid rgb(204, 204, 204); padding-left: 1ex;"># Summary <br> <br>This is a public disclosure of a vulnerability that I previously disclo= sed to <br>the bitcoin-security mailing list. It's an easy vulnerability to fi= x. Although <br>as with other "free" relay attacks I've disclosed, I didn= 't get a substantive <br>response from Bitcoin Core, other than Core closing the my pull-req ena= bling <br>full-RBF by default that would fix this specific vulnerability. <br> <br>But read on, this is quite an odd case of Core politics, and the story = is not <br>as simple as Core refusing to fix a vulnerability. Also, I've inclu= ding a fun <br>homework problem at the end: figure out how TRUC/V3 transactions itself= creates <br>a "free" relay attack. <br> <br> <br># Background <br> <br>This is just one of a few "free" relay attacks that I have re= cently disclosed, <br>including, but not limited to: <br> <br> "A Free-Relay Attack Exploiting RBF Rule #6" - Mar 18th 2= 024 <br> <a href=3D"https://groups.google.com/g/bitcoindev/c/EJYoeNTPVhg" ta= rget=3D"_blank" rel=3D"nofollow" data-saferedirecturl=3D"https://www.google= .com/url?hl=3Den&q=3Dhttps://groups.google.com/g/bitcoindev/c/EJYoeNTPV= hg&source=3Dgmail&ust=3D1721478911283000&usg=3DAOvVaw2tGCUebRo6= vjKF8SKftMMH">https://groups.google.com/g/bitcoindev/c/EJYoeNTPVhg</a> <br> <br> "A Free-Relay Attack Exploiting Min-Relay-Fee Differences"= ; - Mar 31st 2024 <br> <a href=3D"https://groups.google.com/g/bitcoindev/c/3XqfIOYzXqo" ta= rget=3D"_blank" rel=3D"nofollow" data-saferedirecturl=3D"https://www.google= .com/url?hl=3Den&q=3Dhttps://groups.google.com/g/bitcoindev/c/3XqfIOYzX= qo&source=3Dgmail&ust=3D1721478911284000&usg=3DAOvVaw3TOPkBQ_Nd= JKtzd8KxxdVy">https://groups.google.com/g/bitcoindev/c/3XqfIOYzXqo</a> <br> <br>The term "free relay attack" simply refers to any mechanism w= here transaction <br>data can be broadcast at unusually low cost; the "free" in &q= uot;free relay" is a <br>misnomer as all these attacks do in fact have some cost. <br> <br>This particular attack isn't significantly different than the other= attacks <br>I've disclosed. With one important exception: unlike those other at= tacks, <br>fixing this particular attack would be quite easy, by enabling full-rbf= by <br>default. So I disclosed it to the bitcoin-security mailing list as a te= st: does <br>Bitcoin Core actually care about free relay attacks? My hypothesis is t= hat Core <br>does not, as they know full well that "free" relay is an unav= oidable problem; <br>I've received absolutely no feedback from any Bitcoin Core members = for the <br>other disclosed attacks, beyond achow using my disclosure of the RBF Ru= le #6 <br>attack as an excuse to remove me from the bitcoin-security mailing list= . <br> <br>The fact that Core doesn't actually care about "free" rel= ay attacks is relevant <br>to TRUC/V3 Transactions. As per BIP-431: <br> <br> "The primary problem with [RBFR proposals] is the potential fo= r free relay and DDoS attacks. <br> <br> Removing Rule 3 and 4 in general would allow free relay [27]." <br> <a href=3D"https://github.com/bitcoin/bips/blob/812907c2b00b92ee31e= 2b638622a4fe14a428aee/bip-0431.mediawiki#user-content-Alternatives_replace_= by_feerate" target=3D"_blank" rel=3D"nofollow" data-saferedirecturl=3D"http= s://www.google.com/url?hl=3Den&q=3Dhttps://github.com/bitcoin/bips/blob= /812907c2b00b92ee31e2b638622a4fe14a428aee/bip-0431.mediawiki%23user-content= -Alternatives_replace_by_feerate&source=3Dgmail&ust=3D1721478911284= 000&usg=3DAOvVaw3fh7gqD6KbjyJF9u5jDGnE">https://github.com/bitcoin/bips= /blob/812907c2b00b92ee31e2b638622a4fe14a428aee/bip-0431.mediawiki#user-cont= ent-Alternatives_replace_by_feerate</a> <br> <br>I believe the authors of that BIP are fully aware of the fact that &quo= t;free" relay <br>is an unavoidable problem, making their rational for TRUC/V3 bogus, and= don't <br>want to admit that they've wasted a large amount of engineering tim= e on a bad <br>proposal. I will be submitting a pull-req to get BIP-431 corrected, as = the many <br>"free" relay attacks I've disclosed clearly show that cla= iming RBFR would <br>"allow" free relay is simply not true. <br> <br>Notably, full-RBF is _itself_ a transaction pinning fix for many use-ca= ses; <br>part of the TRUC/V3 standard is to force full-RBF behavior for V3 trans= actions. <br>So Core closing my full-RF pull-req is doubling down on TRUC/V3 in a se= cond <br>way, and TRUC/V3 proponents were the ones who tried to get the full-RBF= option <br>removed from Core in the first place. If not for this dumb bit of Core <br>politics, I'm sure my year-old pull-req to enable full-RBF by defau= lt would <br>have been merged many months ago, as almost all hashpower has adopted f= ull-RBF <br>making objections based on "zeroconf" absurd. <br> <br> <br># The Attack <br> <br>If you're a competent Bitcoin engineer, familiar with how mempools = work, you've <br>probably figured it out already based on the title: obviously, if a hig= h <br>percentage of miners are adopting a policy that Bitcoin Core nodes are = not, you <br>can cheaply consume transaction relay bandwidth by simply relaying tran= sations <br>that miners are rejecting. <br> <br>Specifically, do the following: <br> <br>1. Broadcast a small, low-fee-rate, tx A with BIP-125 opt-in disabled. <br>2. Broadcast a full-RBF double-spend of A, A2, with a higher fee-rate. <br>3. Spend the outputs of A in a large, low fee-rate, transaction B with = BIP-125 <br> opt-in enabled. ~100% of miners will reject B, as it spends an input= not in <br> their mempools. However Bitcoin Core nodes will waste bandwidth prop= agating <br> B. <br>4. (Optional) Double-spend B repeatedly. Again, Bitcoin Core nodes will= waste <br> bandwidth propagating Bn's that ~100% of miners are ignoring. <br>5. Double-spend A2 to recover your funds and do it all over again (or i= f A2 had <br> a high enough fee-rate, just wait for it to be mined). <br> <br>The cost to relay each B transaction depends on the fee-rate of B. Sinc= e <br>Bitcoin Core defaults to a fairly large mempool, the minimum relay fee-= rate is <br>typically well below the economic fee-rate required for miners to actua= lly mine <br>a transaction; Core accepts transactions that are uneconomical for mine= rs to <br>mine for the forseeable future. <br> <br>For example, at the moment typical mempools require transactions to pay= at <br>least 1sat/vB, while there are hundreds of MvB worth of transactions pa= ying <br>4sat/vB, the minimum economical fee-rate. Thus, transactions paying les= s than <br>4sat/VB are extremely unlikely to get mined in the nearish future. <br> <br>Concretely, broadcasting B transactions at 1sat/vB, 2sat/vB, and 3sat/v= B would <br>have almost zero cost as the probability of those transactions getting = mined is <br>nearly zero. This is true _regardless_ of what % of miners are mining f= ull-RBF! <br>As long as you can get at least one miner to mine the A double-spend, t= he <br>attack only costs what it cost to get A mined. <br> <br>If B's are broadcast at a higher fee-rate than the minimum economic= al fee-rate, <br>then the % of full-RBF miners matters. For example, if only 99% of mine= rs mine <br>full-RBF, the chance of a B transaction getting mined per block is abou= t 1%, so <br>the amortized cost of broadcasting B is about 1% of whatever total fee = the <br>highest fee-rate variant of B pays. <br> <br>For an attacker who does not need any B to be broadcast, the cost savin= gs to <br>use of relay bandwidth is approximately the ratio of the difference in = size <br>between B and and A. With a maximum standard transaction size of 100KvB= , or <br>400KB serialized size, this ratio is on the order of 5000:1, times the = total <br>number of B variants broadcast, and the % chance of each B being mined;= it's a <br>few orders of magnitude. <br> <br>Of course, as mentioned above, this is just one of *many* "free&qu= ot; relay attacks, <br>so fixing this particular issue doesn't change much. <br> <br> <br># Attackers Who Benefit From B Getting Mined <br> <br>Some attackers actually need B to get mined. For example, imagine an ex= change <br>who needs to do large consolidation transactions. They could use this a= ttack <br>(and some attacks like it) as a way to goad users and miners into minin= g <br>consolidation transactions for them at low cost. In this variant of the= attack, <br>the attacker would pad the size of B with consolidation spends that the= y needed <br>to do anyway. Someone who tried to stop the attack by getting B mined (= eg via <br><a href=3D"http://mempool.space" target=3D"_blank" rel=3D"nofollow" dat= a-saferedirecturl=3D"https://www.google.com/url?hl=3Den&q=3Dhttp://memp= ool.space&source=3Dgmail&ust=3D1721478911284000&usg=3DAOvVaw3LA= 8yoWHtUO8-O7KhNWIld">mempool.space</a>'s transaction accellerator) woul= d simply be paying the attacker's <br>fees for them. <br> <br>Obviously, this strategy is only relevant for B's below the economi= c fee-rate. <br>However, the weaker version of this strategy is to parallize the attack= , and do <br>your consolidation with the _A_ double-spends to reduce the # of bytes = used per <br>full-rbf double-spend. <br> <br> <br># TRUC/V3 Creates a Free Relay Attack <br> <br>I'll leave the details of this as a homework problem. But obviously= , the <br>introduction of TRUC/V3 transactions *itself* creates a free relay atta= ck very <br>similar to the above! Just like full-RBF, not all miners will mine V3 <br>transactions. So you can do the exact same type of attack by taking adv= antage <br>of this difference in mining policy. <br> <br>--=20 <br><a href=3D"https://petertodd.org" target=3D"_blank" rel=3D"nofollow" da= ta-saferedirecturl=3D"https://www.google.com/url?hl=3Den&q=3Dhttps://pe= tertodd.org&source=3Dgmail&ust=3D1721478911284000&usg=3DAOvVaw3= Oozvov6XJ1qRfXOK6i_I7">https://petertodd.org</a> 'peter'[:-1]@<a hr= ef=3D"http://petertodd.org" target=3D"_blank" rel=3D"nofollow" data-safered= irecturl=3D"https://www.google.com/url?hl=3Den&q=3Dhttp://petertodd.org= &source=3Dgmail&ust=3D1721478911284000&usg=3DAOvVaw17SWdmJvOinr= lFD8MBev1B">petertodd.org</a> <br></blockquote></div> <p></p> -- <br /> You received this message because you are subscribed to the Google Groups &= quot;Bitcoin Development Mailing List" group.<br /> To unsubscribe from this group and stop receiving emails from it, send an e= mail to <a href=3D"mailto:bitcoindev+unsubscribe@googlegroups.com">bitcoind= ev+unsubscribe@googlegroups.com</a>.<br /> To view this discussion on the web visit <a href=3D"https://groups.google.c= om/d/msgid/bitcoindev/18a5e5a2-92b3-4345-853d-5a63b71d848bn%40googlegroups.= com?utm_medium=3Demail&utm_source=3Dfooter">https://groups.google.com/d/msg= id/bitcoindev/18a5e5a2-92b3-4345-853d-5a63b71d848bn%40googlegroups.com</a>.= <br /> ------=_Part_159329_1526928484.1721392866788-- ------=_Part_159328_1732340751.1721392866788--