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 8A9EF86D for ; Thu, 7 Jun 2018 22:20:36 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from outmail148095.authsmtp.com (outmail148095.authsmtp.com [62.13.148.95]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id D49C270D for ; Thu, 7 Jun 2018 22:20:35 +0000 (UTC) Received: from mail-c247.authsmtp.com (mail-c247.authsmtp.com [62.13.128.247]) by punt21.authsmtp.com. (8.15.2/8.15.2) with ESMTP id w57MKXEM021838; Thu, 7 Jun 2018 23:20:33 +0100 (BST) (envelope-from user@petertodd.org) Received: from petertodd.org (ec2-52-5-185-120.compute-1.amazonaws.com [52.5.185.120]) (authenticated bits=0) by mail.authsmtp.com (8.15.2/8.15.2) with ESMTPSA id w57MKUhE030682 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Thu, 7 Jun 2018 23:20:31 +0100 (BST) (envelope-from user@petertodd.org) Received: from [127.0.0.1] (localhost [127.0.0.1]) by petertodd.org (Postfix) with ESMTPSA id 8F0A3400B0; Thu, 7 Jun 2018 22:20:30 +0000 (UTC) Received: by localhost (Postfix, from userid 1000) id 6CCD922043; Thu, 7 Jun 2018 18:20:28 -0400 (EDT) Date: Thu, 7 Jun 2018 18:20:28 -0400 From: Peter Todd To: Bram Cohen Message-ID: <20180607222028.zbva4vrv64dzrmxy@petertodd.org> References: <20180607171311.6qdjohfuuy3ufriv@petertodd.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="lvorui2qu73lvhyc" Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-Server-Quench: fde045a1-6aa0-11e8-8791-0015176ca198 X-AuthReport-Spam: If SPAM / abuse - report it at: http://www.authsmtp.com/abuse X-AuthRoute: OCd2Yg0TA1ZIVwkA IjsJECJaVQIpKltL GxAVKBZePFsRUQkR aAdMdgUUEkAaAgsB Am4bWVdeUl17WmE7 bghPaBtcak9QXgdq T0pMXVMcUwBvfGdk XmseURl0fwcIfnZ5 ZQg0CiVbWEErdFt7 Ex9UCGwHMG99YGcW UV1YdwJRcQRMLU5E Y1gxNiYHcQ5VPz4z GA41ejw8IwAXFD5I WR0AIRoXTFwIGjN0 WwoPEH0jEFUZR209 KAZuMVcSEQ4NIg0z N1AlREkZNBlwQhVE GEZDG2dGJkUBQDc3 RQoSRkkQDHVTRj1f agAA X-Authentic-SMTP: 61633532353630.1038:706 X-AuthFastPath: 0 (Was 255) X-AuthSMTP-Origin: 52.5.185.120/25 X-AuthVirus-Status: No virus detected - but ensure you scan with your own anti-virus system. X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,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] 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: Thu, 07 Jun 2018 22:20:36 -0000 --lvorui2qu73lvhyc Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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? Th= at > sounds like a good idea. >=20 > On Thu, Jun 7, 2018 at 10:13 AM, Peter Todd via bitcoin-dev < > bitcoin-dev@lists.linuxfoundation.org> wrote: >=20 > > It's well known that the Bitcoin merkle tree algorithm fails to disting= uish > > between inner nodes and 64 byte transactions, as both txs and inner nod= es > > 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 s= afe > > 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 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. --=20 https://petertodd.org 'peter'[:-1]@petertodd.org --lvorui2qu73lvhyc Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEFcyURjhyM68BBPYTJIFAPaXwkfsFAlsZr6oACgkQJIFAPaXw kftYFwf8DuI6w/F2TNWTpB148T8D+76lYlk08wAWVaVZy4b1MCBtIOVbs7xRA+k4 RWQSML1Zhpo1Gi3JwBAeGFRHKQa/XWG7PRj76FgJlvNtaHVaFMszqbOTGsPXMtX3 f+iVubCxBHNBgCXaAkcuPi7IwVwELGCPP51aq5F1iTiayQPUPnnIFgc1X82jG/Y+ 6t/fEWqO/ZbDk7apzx4zZYD+YndWA1VnjDVbtaL5AmqTfgE6MrVIlmfaDWWoRJlW HWJEGY2iHC1+EXn657hpjEQ7zUF70B+U/Dz5whVsEaAOU2Hwvqwo63jL0yu7clbk m9C4aS3Cfmfha9AhvvTGsZkbncAyYQ== =sog5 -----END PGP SIGNATURE----- --lvorui2qu73lvhyc--