From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-4.v43.ch3.sourceforge.com ([172.29.43.194] helo=mx.sourceforge.net) by sfs-ml-3.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1UpNco-0002Ep-H8 for bitcoin-development@lists.sourceforge.net; Wed, 19 Jun 2013 19:00:58 +0000 Received-SPF: pass (sog-mx-4.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.223.173 as permitted sender) client-ip=209.85.223.173; envelope-from=etotheipi@gmail.com; helo=mail-ie0-f173.google.com; Received: from mail-ie0-f173.google.com ([209.85.223.173]) by sog-mx-4.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1UpNcn-0000dT-Il for bitcoin-development@lists.sourceforge.net; Wed, 19 Jun 2013 19:00:58 +0000 Received: by mail-ie0-f173.google.com with SMTP id k13so14330599iea.32 for ; Wed, 19 Jun 2013 12:00:52 -0700 (PDT) X-Received: by 10.50.136.230 with SMTP id qd6mr2053027igb.4.1371668452227; Wed, 19 Jun 2013 12:00:52 -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 ir8sm7396363igb.6.2013.06.19.12.00.51 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 19 Jun 2013 12:00:51 -0700 (PDT) Message-ID: <51C1FFDA.1050308@gmail.com> Date: Wed, 19 Jun 2013 15:00:42 -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: Adam Back References: <51BFD886.8000701@gmail.com> <20130619142510.GA17239@crunch> <51C1C288.4000305@gmail.com> <20130619152815.GA14729@netbook.cypherspace.org> <20130619183657.GA16708@netbook.cypherspace.org> In-Reply-To: <20130619183657.GA16708@netbook.cypherspace.org> X-Enigmail-Version: 1.5.1 Content-Type: multipart/alternative; boundary="------------050302010302050007010608" X-Spam-Score: -0.6 (/) 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 1.0 HTML_MESSAGE BODY: HTML included in message -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: 1UpNcn-0000dT-Il 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 19:00:58 -0000 This is a multi-part message in MIME format. --------------050302010302050007010608 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit On 06/19/2013 02:36 PM, Adam Back wrote: > This maybe simpler and trivially compatible with existing type2 public > keys > (ones that are multiples of a parent public key): send an ECDSA > signature of > the multiplier, and as we know you can compute ("recover") the parent > public > key from an the ECDSA signature made using it. > > Adam > > On Wed, Jun 19, 2013 at 05:28:15PM +0200, Adam Back wrote: >> [q-th root with unknown no discrete log artefact] >> >> If it was a concern I guess you could require a proof of knowledge of >> discrete log. ie as well as public key parent, multiplier the >> address must >> include ECDSA sig or Schnorr proof of knowledge (which both demonstrate >> knowledge of the discrete log of Q to base G.) It's a cool trick but requiring a signature on each multiplier defeats one of the purposes of a deterministic wallet. I don't want to have to explicitly export a whole bunch of signatures from my offline system just to exercise this address option. The "observer wallet" should be able to do anything it needs to on its own, without help from the offline wallet. Unless you mean that there is a one-time signature from the offline computer that works for all addresses, that can be exported with the observer wallet...? If all you want to do is prove that /someone/ owns that private key, you could send {Sign(MagicString), Multiplier}. So it becomes one signature operation *per wallet*, but creating new wallets would require going back to the offline computer for that one-time signature. That's better than the alternative, but it's still extra bloat for the wallet apps. Either way, I'm not convinced that these are a problem for the specified use cases I outlined. In cases where you have a persistent business relationship, they need to verify the parent public key exchange anyway. After that, the software doesn't technically require the transmission of the PubKey, it only needs the Name/ID of the party and the multiplier and it will fetch the PubKey from its data store. Or it is transmitted and the payer verifies it's correct. Computing an alternate {PubKey', Mult'} that produces the same address and then using it in a MitM attack doesn't work here if the two parties pre-verified the public keys. In the case that a business is checking whether the cashout address of a customer is the same as the last time: if the first payout was not replaced by an attacker, then the business already has the correct public key in their DB and a replacement of further payout requests will fail validation. If the first payout was replaced... well that could've been done anyway (with or without this alternate form), and the customer wouldn't have received their money and the whole process would be flagged and terminated before further transactions. -Alan --------------050302010302050007010608 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit On 06/19/2013 02:36 PM, Adam Back wrote:
This maybe simpler and trivially compatible with existing type2 public keys
(ones that are multiples of a parent public key): send an ECDSA signature of
the multiplier, and as we know you can compute ("recover") the parent public
key from an the ECDSA signature made using it.

Adam

On Wed, Jun 19, 2013 at 05:28:15PM +0200, Adam Back wrote:
[q-th root with unknown no discrete log artefact]

If it was a concern I guess you could require a proof of knowledge of
discrete log.  ie as well as public key parent, multiplier the address must
include ECDSA sig or Schnorr proof of knowledge (which both demonstrate
knowledge of the discrete log of Q to base G.)

It's a cool trick but requiring a signature on each multiplier defeats one of the purposes of a deterministic wallet.  I don't want to have to explicitly export a whole bunch of signatures from my offline system just to exercise this address option.  The "observer wallet" should be able to do anything it needs to on its own, without help from the offline wallet. 

Unless you mean that there is a one-time signature from the offline computer that works for all addresses, that can be exported with the observer wallet...?  If all you want to do is prove that someone owns that private key, you could send {Sign(MagicString), Multiplier}.   So it becomes one signature operation per wallet, but creating new wallets would require going back to the offline computer for that one-time signature.  That's better than the alternative, but it's still extra bloat for the wallet apps.

Either way, I'm not convinced that these are a problem for the specified use cases I outlined.   In cases where you have a persistent business relationship, they need to verify the parent public key exchange anyway.  After that, the software doesn't technically require the transmission of the PubKey, it only needs the Name/ID of the party and the multiplier and it will fetch the PubKey from its data store.  Or it is transmitted and the payer verifies it's correct.  Computing an alternate {PubKey', Mult'} that produces the same address and then using it in a MitM attack doesn't work here if the two parties pre-verified the public keys. 

In the case that a business is checking whether the cashout address of a customer is the same as the last time:  if the first payout was not replaced by an attacker, then the business already has the correct public key in their DB and a replacement of further payout requests will fail validation.  If the first payout was replaced... well that could've been done anyway (with or without this alternate form), and the customer wouldn't have received their money and the whole process would be flagged and terminated before further transactions.

-Alan


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