From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1152AC0172 for ; Wed, 29 Apr 2020 16:00:14 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id F01DB88281 for ; Wed, 29 Apr 2020 16:00:13 +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 ukmPx7nlNcs6 for ; Wed, 29 Apr 2020 16:00:13 +0000 (UTC) X-Greylist: delayed 00:40:45 by SQLgrey-1.7.6 Received: from mail-lj1-f174.google.com (mail-lj1-f174.google.com [209.85.208.174]) by hemlock.osuosl.org (Postfix) with ESMTPS id CE578881D0 for ; Wed, 29 Apr 2020 16:00:12 +0000 (UTC) Received: by mail-lj1-f174.google.com with SMTP id b2so3194469ljp.4 for ; Wed, 29 Apr 2020 09:00:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=satoshilabs.com; s=google; h=mime-version:from:date:message-id:subject:to; bh=ZPC2GhVZiUbEzlxsjE78pXXIwEJtQk1MccFirvtrSFg=; b=LORDlkSoz1RNDgdehjGL0UZ4JCc3Xgec9Y7fA8Wrl8/7LVjAh6Bkwy0Oq7Q5O+1n5F U2eTNlqrad5TV91AkYYS9vyOqMpxOQ7WNt71hyRMN0HWjr0nWPBQseRYHUOTY4qV0gC+ SyUoZ/bmglzbvqbmIL/hgpdazCxfjuMfS5zdO0Wt1hNiQvaAb3f5Oo7BUHouDtV581Qa XREknnDra3p9zsx4QnhHQeX+HIyN55O3o4KbM4mDg4CYQU8XsWmRGlyK/kdvpBcvjAvh sYGAlGrhmzrLMLab8OqejpwOqpEIdjOhagDm2XO5nqPze3nI2UZK6V9U4H5/kZjVgl3i RakQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=ZPC2GhVZiUbEzlxsjE78pXXIwEJtQk1MccFirvtrSFg=; b=td5TxaYg0SKrNAAwsg5xhft7hjcWPohMhT1bpHw3OdfSI4bK9hgAx57IMZh0U0Jmn2 Bd2TJooeOX9Lu/l3TYlDfQZiO17sGL/qX5YCmaBg/tCzRPwcPzb3F2iATw6lbwTsNcc8 6ye7f8fU0cg+6n/4v8BPm2rJ/3Vf6RB/kvQQXHjQK8NF8Y4D+npu1r54kUKIDEGurC2z WpR9SNnFPOf9rgKowGq46DoBPdw3eDkAgjVyIgPiNQ9ek41PwS/KAeFMpdHuTpaId2Il JnFVWIZHCbaugd9E6hben4+P3WSVaAC+6IVJKM3lQLgxGmJVFKpDaSd58dhsgQ3mRXz1 fjHA== X-Gm-Message-State: AGi0PubbYtAPm2Z6DH/AcdWMxXbaW0wnMRDDHYj9AJ3Qq/cOCoLLZ1Z3 JXawXvgow3K/w9iPDQGokC8WgjRiMTrZGya02HWa69MS X-Google-Smtp-Source: APiQypLD+JojXK9qGAU/Uwd4isSZWetMgvsbHibFl2vvwq2yvq6e59exlswVJiijptSxK5M9okzOliTfdkcL9tqNrIY= X-Received: by 2002:a17:906:35d0:: with SMTP id p16mr2875367ejb.77.1588172277719; Wed, 29 Apr 2020 07:57:57 -0700 (PDT) MIME-Version: 1.0 From: Andrew Kozlik Date: Wed, 29 Apr 2020 16:57:46 +0200 Message-ID: To: Bitcoin Protocol Discussion Content-Type: multipart/alternative; boundary="00000000000074d51a05a46f2c7e" X-Mailman-Approved-At: Thu, 30 Apr 2020 08:21:50 +0000 Subject: [bitcoin-dev] BIP-341: Committing to all scriptPubKeys in the signature message 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, 29 Apr 2020 16:00:14 -0000 --00000000000074d51a05a46f2c7e Content-Type: text/plain; charset="UTF-8" Hi everyone, In the current draft of BIP-0341 [1] the signature message commits to the scriptPubKey of the output being spent by the input. I propose that the signature message should commit to the scriptPubKeys of *all* transaction inputs. In certain applications like CoinJoin, a wallet has to deal with transactions containing external inputs. To calculate the actual amount that the user is spending, the wallet needs to reliably determine for each input whether it belongs to the wallet or not. Without such a mechanism an adversary can fool the wallet into displaying incorrect information about the amount being spent, which can result in theft of user funds [2]. In order to ascertain non-ownership of an input which is claimed to be external, the wallet needs the scriptPubKey of the previous output spent by this input. It must acquire the full transaction being spent and verify its hash against that which is given in the outpoint. This is an obstacle in the implementation of lightweight air-gapped wallets and hardware wallets in general. If the signature message would commit to the scriptPubKeys of all transaction inputs, then the wallet would only need to acquire the scriptPubKey of the output being spent without having to acquire and verify the hash of the entire previous transaction. If an attacker would provide an incorrect scriptPubKey, then that would cause the wallet to generate an invalid signature message. Note that committing only to the scriptPubKey of the output being spent is insufficient for this application, because the scriptPubKeys which are needed to ascertain non-ownership of external inputs are precisely the ones that would not be included in any of the signature messages produced by the wallet. The obvious way to implement this is to add another hash to the signature message: sha_scriptPubKeys (32): the SHA256 of the serialization of all scriptPubKeys of the previous outputs spent by this transaction. Cheers, Andrew Kozlik [1] https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki#common-signature-message [2] https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-August/014843.html --00000000000074d51a05a46f2c7e Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Hi everyone,

In the current draft of BIP-0341 [1] t= he signature message commits to the scriptPubKey of the output being spent = by the input. I propose that the signature message should commit to the scr= iptPubKeys of *all* transaction inputs.

In certain applications like= CoinJoin, a wallet has to deal with transactions containing external input= s. To calculate the actual amount that the user is spending, the wallet nee= ds to reliably determine for each input whether it belongs to the wallet or= not. Without such a mechanism an adversary can fool the wallet into displa= ying incorrect information about the amount being spent, which can result i= n theft of user funds [2].

In order to ascertain non-ownership of an= input which is claimed to be external, the wallet needs the scriptPubKey o= f the previous output spent by this input. It must acquire the full transac= tion being spent and verify its hash against that which is given in the out= point. This is an obstacle in the implementation of lightweight air-gapped = wallets and hardware wallets in general. If the signature message would com= mit to the scriptPubKeys of all transaction inputs, then the wallet would o= nly need to acquire the scriptPubKey of the output being spent without havi= ng to acquire and verify the hash of the entire previous transaction. If an= attacker would provide an incorrect scriptPubKey, then that would cause th= e wallet to generate an invalid signature message.

N= ote that committing only to the scriptPubKey of the output being spent is i= nsufficient for this application, because the scriptPubKeys which are neede= d to ascertain non-ownership of external inputs are precisely the ones that= would not be included in any of the signature messages produced by the wal= let.

The obvious way to implement this is to add anothe= r hash to the signature message:
sha_scriptPubKeys (32): the SHA256 of t= he serialization of all scriptPubKeys of the previous outputs spent by this= transaction.

Cheers,
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