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 9871C9E2 for ; Sat, 9 Jun 2018 03:29:33 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-wm0-f52.google.com (mail-wm0-f52.google.com [74.125.82.52]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id E4D885C2 for ; Sat, 9 Jun 2018 03:29:32 +0000 (UTC) Received: by mail-wm0-f52.google.com with SMTP id 69-v6so6880799wmf.3 for ; Fri, 08 Jun 2018 20:29:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chia-net.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=VXbsYwcyEwRHSqvdlngzaTlNrwwzUqi5AStJRp8Yrug=; b=Xy1k8rN9ugYQ5JSytDV55/FPx+c/k/O//AUceHKXsAsZgHbzXs9ktE4aknHHzTBKU9 fyb1aQFyhH0Sy+1b7RYw0nmQlT/CHNZ3qTFVgZJHJFagY+mMhiyR3YvZ5gZtM+WOh52q fxWSAze49bTdAubP/JOmqlkehlCPRgdC7Pu7tm6dDTTVw4CFflvqMlnsejwIjhpVcmym DVnwGJbNvEovf/VYotuLj/Rq63fw04B92vu5YWzJOwgjjlcZ1d6+jHpDOYrzb7Tknsp7 F1XI/sAtmp/EQAajJfN37N8PsGBa5Oop/mcNrLk0DiydH6wet+FvJ+hUbTKyU0r0/C/q L/6A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=VXbsYwcyEwRHSqvdlngzaTlNrwwzUqi5AStJRp8Yrug=; b=fnEmaZDW1QeaEIoy8LW4h5EAyRtQXK0MDe92ulPtUKZuJ4+C1kjrHrCUypV3TVXu4h Bwu2srcMb6j2Qqis2UJAS0DkpPZzAqNf/36r6X3QZ2vbLpUZkN8MmWHjf3HLnW7B9ALu 0QtmgdarDwrdkgccXoio8HcjEhM+9wix3jjbj9fZKe6h+1MrFcmBCL1l3/ku0CIbDpRr itG2pDA/bka30fX0RZSCtBcDw0j2h+5lt2zcbwHPpsK1ZbsWZsxVwMMj1/DZag4wkepa yC3mfwIaBGzsx5nXwwgqpm2oolnMIw7UK1aCVygKjXpt9ZXbVsIYWa/S+JtP533000IV ahgQ== X-Gm-Message-State: APt69E3zS0dK1w1qs4xwm5q9xmaiYj/ZIf96I+c2TJC9OcZ8uSWhVk5E AS+NPPtwEO4C4ukLlcwIzacqNKDXGKRVlQV481rwmHxi X-Google-Smtp-Source: ADUXVKKrHNSYS4U8We/wUsNWjZLOjjJ4f/RYaL5F+8fI+NhH6rucDQlg67sZu5rk2o5rJ+t+ikblgl1gCdcN9xfMqaA= X-Received: by 2002:a1c:9f06:: with SMTP id i6-v6mr2783041wme.73.1528514971454; Fri, 08 Jun 2018 20:29:31 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a1c:b984:0:0:0:0:0 with HTTP; Fri, 8 Jun 2018 20:29:30 -0700 (PDT) X-Originating-IP: [65.200.105.218] In-Reply-To: <20180607222028.zbva4vrv64dzrmxy@petertodd.org> References: <20180607171311.6qdjohfuuy3ufriv@petertodd.org> <20180607222028.zbva4vrv64dzrmxy@petertodd.org> From: Bram Cohen Date: Fri, 8 Jun 2018 20:29:30 -0700 Message-ID: To: Peter Todd Content-Type: multipart/alternative; boundary="000000000000e85efc056e2d1f66" X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, HTML_MESSAGE, RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org X-Mailman-Approved-At: Sat, 09 Jun 2018 03:30:45 +0000 Cc: Bitcoin Protocol Discussion Subject: Re: [bitcoin-dev] Trusted merkle tree depth for safe tx inclusion 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: Sat, 09 Jun 2018 03:29:33 -0000 --000000000000e85efc056e2d1f66 Content-Type: text/plain; charset="UTF-8" So are you saying that if fully validating nodes wish to prune they can maintain the ability to validate old transactions by cacheing the number of transactions in each previous block? On Thu, Jun 7, 2018 at 3:20 PM, Peter Todd wrote: > On Thu, Jun 07, 2018 at 02:15:35PM -0700, Bram Cohen wrote: > > Are you proposing a soft fork to include the number of transactions in a > > block in the block headers to compensate for the broken Merkle format? > That > > sounds like a good idea. > > > > On Thu, Jun 7, 2018 at 10:13 AM, Peter Todd via bitcoin-dev < > > bitcoin-dev@lists.linuxfoundation.org> wrote: > > > > > It's well known that the Bitcoin merkle tree algorithm fails to > distinguish > > > between inner nodes and 64 byte transactions, as both txs and inner > nodes > > > are > > > hashed the same way. This potentially poses a problem for tx inclusion > > > proofs, > > > as a miner could (with ~60 bits of brute forcing) create a transaction > that > > > committed to a transaction that was not in fact in the blockchain. > > > > > > Since odd-numbered inner/leaf nodes are concatenated with themselves > and > > > hashed > > > twice, the depth of all leaves (txs) in the tree is fixed. > > > > > > It occured to me that if the depth of the merkle tree is known, this > > > vulnerability can be trivially avoided by simply comparing the length > of > > > the > > > merkle path to that known depth. For pruned nodes, if the depth is > saved > > > prior > > > to pruning the block contents itself, this would allow for completely > safe > > > verification of tx inclusion proofs, without a soft-fork; storing this > ^^^^^^^^^^^^^^^^^^^ > > Re-read my post: I specifically said you do not need a soft-fork to > implement > this. In fact, I think you can argue that this is an accidental feature, > not a > bug, as it further encourages the use of safe full verifiaction rather than > unsafe lite clients. > > -- > https://petertodd.org 'peter'[:-1]@petertodd.org > --000000000000e85efc056e2d1f66 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
So are you saying that if fully validating nodes wish to p= rune they can maintain the ability to validate old transactions by cacheing= the number of transactions in each previous block?

On Thu, Jun 7, 2018 at 3:20 PM, Pet= er Todd <pete@petertodd.org> wrote:
On Thu, Jun 07, 2018 at 02:15:35PM -0700, Br= am Cohen wrote:
> Are you proposing a soft fork to include the number of transactions in= a
> block in the block headers to compensate for the broken Merkle format?= That
> sounds like a good idea.
>
> On Thu, Jun 7, 2018 at 10:13 AM, Peter Todd via bitcoin-dev <
> bitcoin-dev@l= ists.linuxfoundation.org> wrote:
>
> > It's well known that the Bitcoin merkle tree algorithm fails = to distinguish
> > between inner nodes and 64 byte transactions, as both txs and inn= er nodes
> > are
> > hashed the same way. This potentially poses a problem for tx incl= usion
> > proofs,
> > as a miner could (with ~60 bits of brute forcing) create a transa= ction that
> > committed to a transaction that was not in fact in the blockchain= .
> >
> > Since odd-numbered inner/leaf nodes are concatenated with themsel= ves and
> > hashed
> > twice, the depth of all leaves (txs) in the tree is fixed.
> >
> > It occured to me that if the depth of the merkle tree is known, t= his
> > vulnerability can be trivially avoided by simply comparing the le= ngth of
> > the
> > merkle path to that known depth. For pruned nodes, if the depth i= s saved
> > prior
> > to pruning the block contents itself, this would allow for comple= tely safe
> > verification of tx inclusion proofs, without a soft-fork; storing= this
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2= =A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0^^^^^^^^^^^^^^^^^^^

Re-read my post: I specifically said you do not need a soft-fork to impleme= nt
this. In fact, I think you can argue that this is an accidental feature, no= t a
bug, as it further encourages the use of safe full verifiaction rather than=
unsafe lite clients.

--
http= s://petertodd.org 'peter'[:-1]@petertodd.org

--000000000000e85efc056e2d1f66--