From mboxrd@z Thu Jan 1 00:00:00 1970 Delivery-date: Tue, 06 Oct 2026 14:36:34 -0700 Received: from mail-oa1-f63.google.com ([209.85.160.63]) by mail.fairlystable.org with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from ) id 1xECpt-00044z-PR for bitcoindev@gnusha.org; Tue, 06 Oct 2026 14:36:34 -0700 Received: by mail-oa1-f63.google.com with SMTP id 586e51a60fabf-451d80641efsf4651967fac.2 for ; Tue, 06 Oct 2026 14:36:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlegroups.com; s=20251104; t=1791322587; x=1791927387; darn=gnusha.org; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:x-original-sender:content-type :mime-version:subject:message-id:to:from:date:sender:from:to:cc :subject:date:message-id:reply-to:content-type; bh=WnjRRx9P2IMiXtLvHGHLZyXVGV+TYj8cWAcU1DAYzy8=; b=DfUSGmsQJSrYV2gUbyltyAZxGDR1/VUGvtFhQPS0XjTBZnHrMHI8eLJzTKRpgIAjbC yk8c1/qatgQGlpEmk9eJijljGUYbv9vH58nKIS/53tMlw8/8vP9LWoEnCJX46AzCFKSw WOmtrK6pwVFjbFb9i0H5v2pQcgcuc829uD1QLCYO2eMUfv3hmFGpfodYnencQL244Qdb w0H2XqOSYqRDJ+VxMskNtcc46I7JCs71J+bePs905KPMBjK/bM2/LXjx7V6eJf6M5cUL 5ZaYefymbaDl9xs9kQ21vujmSeiKkh62tBifiu0/Yw0M/G/JslQIBBVZq868HSEUp47w y13Q== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1791322587; x=1791927387; darn=gnusha.org; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:x-original-sender:content-type :mime-version:subject:message-id:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=WnjRRx9P2IMiXtLvHGHLZyXVGV+TYj8cWAcU1DAYzy8=; b=QTp2sMZJ2ziTUxRInfkMnKb5kFtZD4g67SHvdbMyzyj5Wooo77PTIcLDrYpPJEgttT GNCk6feSQ1s+ILaM887/Ztobb1ZTgXNgmv9ozNI7kJCcHf4yrfpJukiFeqWUu7oyS3V/ DVpNQI/xRWkjLGASHxbxDHi4ij+nTRc4/9b9bHn0F9W5GOIce3WUTJhVyAHNeyVZP9r8 Si+BFJgOALRG1n/MWUqTVdqIoIMhYB2sGxTnwpuF1Y1TiqC80/j1r5QLFij/cVD6G32y ZsJ8bPpNcuaY6d3fNFcszrOt/n4rZYuVf9Hs5tQMHKwrEMgcqf0f1NI+rwTNA5Ta6uCR YLSQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1791322587; x=1791927387; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:x-original-sender:content-type :mime-version:subject:message-id:to:from:date:x-beenthere :x-gm-message-state:sender:from:to:cc:subject:date:message-id :reply-to:content-type; bh=WnjRRx9P2IMiXtLvHGHLZyXVGV+TYj8cWAcU1DAYzy8=; b=VuRKcyGIwhSJzX6q+Eg+jHPEG3Rq4lyv8pYplu7IAQny/JFXo93qxktUBwkznREAKj jC2xheXJN/oSUlnvylLsQd+68AkvhAqjAh3nT+bAlRZ0MnpK9fhwbXEzDeWLugS9SduR JTz62wJlldVG9h4NLGaTgse6PXpWgmvok58z6XUk9V+UrQBoPxGQsr9mtZ75LDqi1s2s 6zPpPyLsY7cdSaR/BebXKVIv0URRgzuX71+7/c3QjNX0Uv7zZQpTw3UuvRO9EKyNd51M xIGsy1t8nJHT6oUIxTw7SBAH2V8gO8xpuAzzl1Pi1oVRbY4q+brHx8WTTJtwmvj/wH3b Xk1Q== Sender: bitcoindev@googlegroups.com X-Forwarded-Encrypted: i=1; AKwUvBxAHrQ3NqCVHuqBR7ef0jQLDZSOw8zn1KYnbPNIqfn2ceGRwNFJK123q2aS5QBsoqnhAUpeb3r6HS/2@gnusha.org X-Gm-Message-State: AFuF++nMWv1wRX3AyqTq9UZ/SCmmxlxtgzr4XpboNOqQaOC8dtnSYYkq J2/NRC7yJmuG5X6kqwXMTZRv+Va6lwZEr+XXUh++DipiULCWq28AW4XJ X-Received: by 2002:a05:6871:7381:b0:46a:8e29:4a03 with SMTP id 586e51a60fabf-4a25956e82dmr302480fac.13.1791322587412; Tue, 06 Oct 2026 14:36:27 -0700 (PDT) X-BeenThere: bitcoindev@googlegroups.com; h="ATskLdc6r+RARo4RO9VwNqrOmDNckoBWx/6URR+rd0XeTWTcmQ==" Received: by 2002:a05:6871:eb12:b0:49d:faf9:48cf with SMTP id 586e51a60fabf-4a253a5ae19ls674100fac.2.-pod-prod-03-us; Tue, 06 Oct 2026 14:36:20 -0700 (PDT) X-Received: by 2002:a05:6808:13d6:b0:4f3:e98f:fa26 with SMTP id 5614622812f47-4fc46c98650mr528691b6e.58.1791322580834; Tue, 06 Oct 2026 14:36:20 -0700 (PDT) Received: by 2002:a05:690c:8691:20b0:8ae:b617:7167 with SMTP id 00721157ae682-8b05aee5583ms7b3; Tue, 6 Oct 2026 14:05:37 -0700 (PDT) X-Received: by 2002:a05:690c:c505:b0:8ae:b617:713f with SMTP id 00721157ae682-8b05af73dc4mr3082597b3.53.1791320736437; Tue, 06 Oct 2026 14:05:36 -0700 (PDT) Date: Tue, 6 Oct 2026 14:05:36 -0700 (PDT) From: Ori Newman To: Bitcoin Development Mailing List Message-Id: <2e554c89-a2a1-4bcf-941c-32f6a8ba9567n@googlegroups.com> Subject: [bitcoindev] RE BIP 300: 26% censoring attack MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_12210_977927440.1791320736156" X-Original-Sender: OriNewman1@gmail.com Precedence: list Mailing-list: list bitcoindev@googlegroups.com; contact bitcoindev+owners@googlegroups.com List-ID: X-Google-Group-Id: 786775582512 List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , X-Spam-Score: -0.5 (/) ------=_Part_12210_977927440.1791320736156 Content-Type: multipart/alternative; boundary="----=_Part_12211_1542023487.1791320736156" ------=_Part_12211_1542023487.1791320736156 Content-Type: text/plain; charset="UTF-8" It seems like a 26% attacker can censor BIP 300 bundles indefinitely: Assume some drivechain publishes a valid bundle, the attacker can send ALARM messages in all of her blocks to reduce its score by 1 in each block. Since the expected score increase per block is 0.74 - 0.26 = 0.48, its expected score in the 26300 block window is 0.48 * 26300 = 12624, which is less than the required score of 13150, so the bundle will almost certainly fail (this is only an approximation, since hitting the 13150 wall at any point is enough for the bundle to get accepted). I think the fix to it should be quite simple: once we forbid ALARM messages or any kind of downvote, we can revert to the honest majority security assumption - a proposal with 51% support will almost certainly succeed to pass the threshold, and a proposal with 49% support will almost certainly fail to pass it. If this is intentional, I suggest changing the BIP to reflect the 75% honest majority assumption, since this is a strong deviation from Bitcoin's security model (one argument for it would be to make it extra difficult for an attacker with less than 75% of the hashrate to steal funds). If this is not intentional, I suggest to forbid ALARM messages or any kind of downvote, so we revert to the 50% honest majority security assumption - a proposal with 51% support will almost certainly succeed to pass the threshold, and a proposal with 49% support will almost certainly fail to pass it. -- 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 email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/2e554c89-a2a1-4bcf-941c-32f6a8ba9567n%40googlegroups.com. ------=_Part_12211_1542023487.1791320736156 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
It seems like a 26% attacker can censor BIP 300 bundles indefinitely:<= /div>

Assume some drivechain publishes a valid bundle,= the attacker can send ALARM messages in all of her blocks to reduce its sc= ore by 1 in each block. Since the expected score increase per block is 0.74= - 0.26 =3D 0.48, its expected score in the 26300 block window is 0.48 * 26= 300 =3D=C2=A012624, which is less than the required score of 13150, s= o the bundle will almost certainly fail=C2=A0(this is only an = approximation, since hitting the 13150 wall at any point is enough for the = bundle to get accepted).

I think the fix to it should be quite simple: once we forbid ALARM messa= ges or any kind of downvote, we can revert to the honest majority security = assumption - a proposal with 51% support will almost certainly succeed to p= ass the threshold, and a proposal with 49% support will almost certainly fa= il to pass it.

If this is in= tentional, I suggest changing the BIP to reflect the 75% honest majority as= sumption, since this is a strong deviation from Bitcoin's security model (o= ne argument for it would be to make it extra difficult for an attacker with= less than 75% of the hashrate to steal funds). If this is not intentional,= I suggest to=C2=A0forbid ALARM messages or any kind of downvote, so = we revert to the 50% honest majority security assumption - a proposal with = 51% support will almost certainly succeed to pass the threshold, and a prop= osal with 49% support will almost certainly fail to pass it.

--
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