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 C7B8F1BB for ; Thu, 18 Aug 2016 00:34:05 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-qk0-f179.google.com (mail-qk0-f179.google.com [209.85.220.179]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 32154238 for ; Thu, 18 Aug 2016 00:34:05 +0000 (UTC) Received: by mail-qk0-f179.google.com with SMTP id t7so3467727qkh.1 for ; Wed, 17 Aug 2016 17:34:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=qJGkPo/dy44zX9w11FfccBwRto/RkfzydR186Y4IKic=; b=JM+on/U0e3+LzoCLAEZST05SopKF2wY0wouD5wPmFRLqU5bncmPUZHTs9AyejLRlxT sNM+oUsxd8zLD+AA8ucmnJaPuuRI8PNWcjSz2ig6sPW55yM559+u7O1dkJPwkVRbq84n YNafvWzJb5S31He9Tc6DVToiOWr8eoXajwgaHhpDnuqwk6ZVPX31uMe/02UtMd7iHU/b 3nygkipVoVq1L6JeIglwjqDTq7Ng9eWZhn6hkSqBgpGbeddX3X926tbZXsFWyzr0jna9 0dCawExp4KSbPS3FF3Z5YBJKIWX+IY7N7MSm3w+BX8I8zJOAsPYeI3pVlxxwxdx4wyPX vr/w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=qJGkPo/dy44zX9w11FfccBwRto/RkfzydR186Y4IKic=; b=YNpuT9vLTUVTkrusXt9S/lSrfcrK17KcX7ikustRNIqVE2dhCTN7VoDIwp6w2Z5NE8 WK7a3cmPYW05QWdZL+2HRl0vaamox8mutjH4MmzXzRitpcouWKNkS7+IsI6c2FhhPRCn iILhxPS7UorylPj3vR5M05P40Gk7JK97rMIxz6LydZZc8YQf9sfGYBq2PzHGpDQQZyox jiD+bmRb4dyHtt9joFbkTFfnYu8DRRSPm7PEmVFH2PnAiy4DrIanDPwhg0cnQsEHTyZH cG4it4axvDY/nEDpDqFGwW9Hjkt7WzBoENW6F6lnlte95oexOUdyTQH4ejTGvDu4O5sM QpgQ== X-Gm-Message-State: AEkoouve7zahxFb33WqEK0SE31CsFaTU1bR40go/MMcCw5xTuQb2DDs5bVw+OWfTUO+Ur+0QY5VG1d65WWaroQ== X-Received: by 10.55.5.17 with SMTP id 17mr48162700qkf.279.1471480444467; Wed, 17 Aug 2016 17:34:04 -0700 (PDT) MIME-Version: 1.0 Received: by 10.200.46.221 with HTTP; Wed, 17 Aug 2016 17:33:24 -0700 (PDT) In-Reply-To: References: <1736097121.90204.1471369988809@privateemail.com> <976728541.94211.1471402973613@privateemail.com> <201608170440.35767.luke@dashjr.org> <703193091.96057.1471428948569@privateemail.com> From: Sergio Demian Lerner Date: Wed, 17 Aug 2016 21:33:24 -0300 Message-ID: To: Gregory Maxwell Content-Type: multipart/alternative; boundary=001a11488a682fbd5c053a4dbdbf X-Spam-Status: No, score=-2.7 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,HTML_MESSAGE,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 Cc: Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] New BIP: Dealing with OP_IF and OP_NOTIF malleability in P2WSH 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: Thu, 18 Aug 2016 00:34:05 -0000 --001a11488a682fbd5c053a4dbdbf Content-Type: text/plain; charset=UTF-8 On Wed, Aug 17, 2016 at 9:19 PM, Gregory Maxwell wrote: > On Thu, Aug 18, 2016 at 12:11 AM, Sergio Demian Lerner via bitcoin-dev > wrote: > > I think that we're not attacking the real source of the problem: that the > > witness data size is not signed. > > It's not possible to do that for the general case, since you may not > even know the witness size in advance (even for checksig's ECDSA, the > encoding is variable sized). > > That's why scripts can check a maximum witness size, and not necessarily an exact value. I think that is overly focusing on "someone might change the feerate", > yes that is an example of an undesirable witness tampering, but it's > not the only one. > > I don't think fees are the problem. There is another problem. Let me re-explain. If I send a transaction to an IoT device (say to an OpenDime or to the old Firmcoin), and the OpenDime must verify that the transaction has been mined (SPV verification), then it may expect the witness program to be of certain maximum size (an implementation-imposed limit). If a Miner modifies the witness size and makes it too large, then the device may not be able to accept the transaction and the bitcoins may be lost. Lost because the private key is in the device, and because the device cannot accept that cloned transaction, never ever. The same is true (although less strict) for side-chains and drive-chains: they may have certain restrictions on the size of transactions they accept to lock bitcoins. That's why I'm proposing that a transaction becomes INVALID if the witness size is higher than the expected size (by the sender). --001a11488a682fbd5c053a4dbdbf Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Wed, Aug 17, 2016 at 9:19 PM, Gregory Maxwell <= gmaxwell@gmail.com<= /a>> wrote:
On= Thu, Aug 18, 2016 at 12:11 AM, Sergio Demian Lerner via bitcoin-dev
<bitcoin-dev@li= sts.linuxfoundation.org> wrote:
> I think that we're not attacking the real source of the problem: t= hat the
> witness data size is not signed.

It's not possible to do that for the general case, since you may= not
even know the witness size in advance (even for checksig's ECDSA, the encoding is variable sized).

That's why scripts can check a maximum witness si= ze, and not necessarily an exact value.


I think that is overly focusing on "someone might change the feerate&q= uot;,
yes that is an example of an undesirable witness tampering, but it's not the only one.

I don't think fees are the problem. There is another= problem. Let me re-explain.
If I send a transaction to an IoT device (= say to an OpenDime or to the old Firmcoin), and the OpenDime must verify th= at the transaction has been mined (SPV verification), then it may expect th= e witness program to be of certain maximum size (an implementation-imposed= =C2=A0 limit). If a Miner modifies the witness size and makes it too large,= then the device may not be able to accept the transaction and the bitcoins= may be lost. Lost because the private key is in the device, and because th= e device cannot accept that cloned transaction, never ever.

The same= is true (although less strict) for side-chains and drive-chains: they may = have certain restrictions on the size of transactions they accept to lock b= itcoins.

That's why I'm pro= posing that a transaction becomes INVALID if the witness size is higher tha= n the expected size (by the sender).


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