From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-4.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1UpJXd-0000S1-W8 for bitcoin-development@lists.sourceforge.net; Wed, 19 Jun 2013 14:39:22 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.223.170 as permitted sender) client-ip=209.85.223.170; envelope-from=etotheipi@gmail.com; helo=mail-ie0-f170.google.com; Received: from mail-ie0-f170.google.com ([209.85.223.170]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1UpJXb-0001oz-7z for bitcoin-development@lists.sourceforge.net; Wed, 19 Jun 2013 14:39:21 +0000 Received: by mail-ie0-f170.google.com with SMTP id e11so13620356iej.15 for ; Wed, 19 Jun 2013 07:39:14 -0700 (PDT) X-Received: by 10.50.11.13 with SMTP id m13mr9910145igb.32.1371652753955; Wed, 19 Jun 2013 07:39:13 -0700 (PDT) Received: from [192.168.1.85] (c-76-111-96-126.hsd1.md.comcast.net. [76.111.96.126]) by mx.google.com with ESMTPSA id fu2sm6414496igb.3.2013.06.19.07.39.13 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 19 Jun 2013 07:39:13 -0700 (PDT) Message-ID: <51C1C288.4000305@gmail.com> Date: Wed, 19 Jun 2013 10:39:04 -0400 From: Alan Reiner User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: timo.hanke@web.de References: <51BFD886.8000701@gmail.com> <20130619142510.GA17239@crunch> In-Reply-To: <20130619142510.GA17239@crunch> X-Enigmail-Version: 1.5.1 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Spam-Score: -1.6 (-) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -1.5 SPF_CHECK_PASS SPF reports sender host as permitted sender for sender-domain 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (etotheipi[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature X-Headers-End: 1UpJXb-0001oz-7z Cc: Bitcoin Dev Subject: Re: [Bitcoin-development] Optional "wallet-linkable" address format - Payment Protocol X-BeenThere: bitcoin-development@lists.sourceforge.net X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Jun 2013 14:39:22 -0000 On 06/19/2013 10:25 AM, Timo Hanke wrote: > Since you mention to use this in conjunction with the payment protocol, > note the following subtlety. Suppose the payer has to paid this address > called "destination": >> Standard Address ~ Base58(0x00 || hash160(PubKeyParent * Multiplier[i]) || >> checksum) > Also suppose the payee has spent the output, i.e. the pubkey > corresponding to "destination", which is PubKeyParent * Multiplier[i], > is publicly known. Then anybody can (in retrospect) create arbitrary > many pairs {PublicKeyParent, Multiplier} (in particular different > PublicKeyParent) that lead to the same "destination". > > Depending on what you have in mind that the transaction should "prove" > regarding its actual receiver or regarding the receiver's PubKeyParent, > this could be an unwanted feature (or it could be just fine). If it is > unwanted then I suggest replacing > PubKeyParent * Multiplier[i] by > PubKeyParent * HMAC(Multiplier[i],PubKeyParent) > which eliminates from the destination all ambiguity about PubKeyParent. > > This modification would not be directly compatible with BIP32 anymore > (unfortunately), but seems to be better suited for use in conjunction > with a payment protocol. > > Timo It's an interesting observation, but it looks like the most-obvious attack vector is discrete log problem: spoofing a relationship between a target public key and one that you control. For instance, if you see {PubA, Mult} produces PubB and you have PubC already in your control that you want to "prove" [maliciously] is related to PubB, then you have to find the multiplier, M that solves: M*PubC = PubB. That's a discrete logarithm problem. I'm not as familiar as you are, with the available operations on elliptic curves, but it sounds like you can produce essentially-random pairs of {PubX, Mult} pairs that give the same PubB, but you won't have the private key associated with those public keys. It's an interesting point, and there may be a reason to be concerned about it. Though, I don't see it yet. -Alan