From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-3.v43.ch3.sourceforge.com ([172.29.43.193] helo=mx.sourceforge.net) by sfs-ml-3.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1UphQI-00008m-V1 for bitcoin-development@lists.sourceforge.net; Thu, 20 Jun 2013 16:09:23 +0000 Received-SPF: pass (sog-mx-3.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.216.41 as permitted sender) client-ip=209.85.216.41; envelope-from=etotheipi@gmail.com; helo=mail-qa0-f41.google.com; Received: from mail-qa0-f41.google.com ([209.85.216.41]) by sog-mx-3.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1UphQD-0006a5-3N for bitcoin-development@lists.sourceforge.net; Thu, 20 Jun 2013 16:09:22 +0000 Received: by mail-qa0-f41.google.com with SMTP id f14so1222932qak.14 for ; Thu, 20 Jun 2013 09:09:11 -0700 (PDT) X-Received: by 10.49.71.70 with SMTP id s6mr1124799qeu.66.1371744551577; Thu, 20 Jun 2013 09:09:11 -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 j5sm1560691qan.7.2013.06.20.09.09.10 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 20 Jun 2013 09:09:10 -0700 (PDT) Message-ID: <51C32926.10904@gmail.com> Date: Thu, 20 Jun 2013 12:09:10 -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: bitcoin-development@lists.sourceforge.net References: <51BFD886.8000701@gmail.com> <20130619142510.GA17239@crunch> <51C1C288.4000305@gmail.com> <20130619152815.GA14729@netbook.cypherspace.org> <20130620074830.GA21724@crunch> <66577F722D29461D8651DF1D0684AAE1@LAPTOPAIR> In-Reply-To: <66577F722D29461D8651DF1D0684AAE1@LAPTOPAIR> X-Enigmail-Version: 1.5.1 Content-Type: multipart/alternative; boundary="------------060104010105000204080005" 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: 1UphQD-0006a5-3N 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: Thu, 20 Jun 2013 16:09:23 -0000 This is a multi-part message in MIME format. --------------060104010105000204080005 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit On 06/20/2013 05:10 AM, Jeremy Spilman wrote: >> which could involve proving something to a third party that has not seen >> the communication between payer and payee. > OK - I think I follow now. So a third-party who does not see any of the > communication between the payer and payee only knows the HASH160. Let's say > the payee denies receipt of the funds.... > > It's easy to prove what public key it was sent to (it's the preimage), but > you can't prove the parent of that public key. You can provide any number of > ParentPubKey * Multiplier that could have been used, so the 3rd party is > unconvinced by a "matching" ParentPubKey * Multiplier. > > However, if you calculated the destination using: PubKeyParent * > HMAC(Multiplier,PubKeyParent) as Timo said, now if you give the 3rd party a > PubKeyParent and Multiplier (or Addend) that produces the destination > address, you've proven the payment is in fact spendable by PubKeyParent, and > they can't deny receipt. Very cool. > > Sorry for "echoing" this back, it took me a little while to work it out, so > I thought I'd write it down. Hope I got it right... > > If you give {PubKey, ChainCode} you do get this feature. If you give > {ParentPubKey, Addend} or {ParentPubKey, Addend, ChainCode} you're back to > having plausible deniability. > > If BIP32's CKD'((Kpar, cpar), i) was actually HMAC(HMAC(cpar, i), Kpar) you > could give HMAC(cpar, i) instead of Addend, and then you would get this > feature; a way to 'skip down' a level in the wallet hierarchy, keep the > 'chain of custody' so to speak back to the ParentPubKey intact, without > having to disclose the ChainCode. Meh... > > I agree, if we used Timo's suggestion, that seems to clean up the remaining uncertainties with this recommendation. I'm not convinced those uncertainties matter in this situation, where there is no question about the parent public key. That is the part of the process that was already verified, per my previous examples. But certainly, for this to be more versatile it would need that. If I modify my request to match Timo's recommendation, then it loses the benefit of being a simple, non-disruptive extension of BIP 32. I'm not fond of deviating from BIP 32, as it kind of defeats one of the benefits of BIP 32: standardization. And I'm not inclined to make an Armory-specific wallet variant. But I can't tell if the benefits are lost on you, or you just don't think they are worth it (or I'm overstating them). I'm strongly opposed to bring extra wallets/chains into this equation /*just*/ to get a benefit that can be had with a simple alternative encoding. This isn't a question of which is better, it's a matter of recognizing that both forms have usefulness and should both be supported. -Alan --------------060104010105000204080005 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit
On 06/20/2013 05:10 AM, Jeremy Spilman wrote:
which could involve proving something to a third party that has not seen 
the communication between payer and payee.

OK - I think I follow now.  So a third-party who does not see any of the 
communication between the payer and payee only knows the HASH160.  Let's say 
the payee denies receipt of the funds....

It's easy to prove what public key it was sent to (it's the preimage), but 
you can't prove the parent of that public key. You can provide any number of 
ParentPubKey * Multiplier that could have been used, so the 3rd party is 
unconvinced by a "matching" ParentPubKey * Multiplier.

However, if you calculated the destination using: PubKeyParent * 
HMAC(Multiplier,PubKeyParent) as Timo said, now if you give the 3rd party a 
PubKeyParent and Multiplier (or Addend) that produces the destination 
address, you've proven the payment is in fact spendable by PubKeyParent, and 
they can't deny receipt. Very cool.

Sorry for "echoing" this back, it took me a little while to work it out, so 
I thought I'd write it down. Hope I got it right...

If you give {PubKey, ChainCode} you do get this feature. If you give 
{ParentPubKey, Addend} or {ParentPubKey, Addend, ChainCode} you're back to 
having plausible deniability.

If BIP32's CKD'((Kpar, cpar), i) was actually HMAC(HMAC(cpar, i), Kpar) you 
could give HMAC(cpar, i) instead of Addend, and then you would get this 
feature; a way to 'skip down' a level in the wallet hierarchy, keep the 
'chain of custody' so to speak back to the ParentPubKey intact, without 
having to disclose the ChainCode. Meh...

I agree, if we used Timo's suggestion, that seems to clean up the remaining uncertainties with this recommendation.   I'm not convinced those uncertainties matter in this situation, where there is no question about the parent public key.  That is the part of the process that was already verified, per my previous examples.  But certainly, for this to be more versatile it would need that. 

If I modify my request to match Timo's recommendation, then it loses the benefit of being a simple, non-disruptive extension of BIP 32.   I'm not fond of deviating from BIP 32, as it kind of defeats one of the benefits of BIP 32:  standardization.   And I'm not inclined to make an Armory-specific wallet variant.

But I can't tell if the benefits are lost on you, or you just don't think they are worth it (or I'm overstating them).  I'm strongly opposed to bring extra wallets/chains into this equation *just* to get a benefit that can be had with a simple alternative encoding.  This isn't a question of which is better, it's a matter of recognizing that both forms have usefulness and should both be supported. 

-Alan
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