From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-2.v43.ch3.sourceforge.com ([172.29.43.192] helo=mx.sourceforge.net) by sfs-ml-2.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1W2Pe6-0002SK-Mw for bitcoin-development@lists.sourceforge.net; Sun, 12 Jan 2014 18:20:26 +0000 Received-SPF: pass (sog-mx-2.v43.ch3.sourceforge.com: domain of taplink.co designates 50.117.27.232 as permitted sender) client-ip=50.117.27.232; envelope-from=jeremy@taplink.co; helo=mail.taplink.co; Received: from mail.taplink.co ([50.117.27.232]) by sog-mx-2.v43.ch3.sourceforge.com with smtp (Exim 4.76) id 1W2Pe4-0002oG-Pm for bitcoin-development@lists.sourceforge.net; Sun, 12 Jan 2014 18:20:26 +0000 Received: from laptop-air.hsd1.ca.comcast.net ([192.168.168.135]) by mail.taplink.co ; Sun, 12 Jan 2014 10:28:46 -0800 Content-Type: multipart/alternative; boundary=----------svoj35mbC6KPQXlw6JqQzt To: "bitcoin-development@lists.sourceforge.net" References: <20140106120338.GA14918@savin> <20140110102037.GB25749@savin> Date: Sun, 12 Jan 2014 10:20:18 -0800 MIME-Version: 1.0 From: "Jeremy Spilman" Organization: TapLink Message-ID: In-Reply-To: User-Agent: Opera Mail/1.0 (Win32) oclient: 192.168.168.135#jeremy@taplink.co#465 X-Spam-Score: -0.7 (/) 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 SPF_PASS SPF: sender matches SPF record -0.1 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 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: 1W2Pe4-0002oG-Pm Subject: Re: [Bitcoin-development] Stealth Addresses 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: Sun, 12 Jan 2014 18:20:26 -0000 ------------svoj35mbC6KPQXlw6JqQzt Content-Type: text/plain; charset=iso-8859-15; format=flowed; delsp=yes Content-Transfer-Encoding: 7bit > You can always just extend the payment protocol with the new fields as > well, vs making very long addresses. I should have mentioned that as Task #4. Agree it could be an optional extension and backward compatible. I think for displaying the payment in the UI after it's been made via PP, we have to fully support sending to a new standard address type anyway. Probably easiest to implement in PP after the address and transaction building code is done. So '4a' would be building a static PP file given the necessary inputs. When I get to that point, I'll send out a draft PP extension with fields/formats if someone else hasn't already. '4b' would be actually adding support for parsing those fields and generating the new transaction type into bitcoind. Any thoughts on the prefix, and one vs two pubkey approach? First of all, do we try to support both equally, or favor one over the other? I was thinking we could have two different 4 byte prefixes but that both render as xSTL/tSTL in Base58 but correspond to the one vs two pubkeys expected. I think the chance of finding a single prefix which looks like xSTL for both address lengths is 1 in (58^4)^2, so that's probably not going to happen. From the payer/user perspective, short stealth vs. long stealth is irrelevant; they both have the same usability properties from the payer perspective. So giving them the same Base58 prefix seems like a good plan. The full 4-byte prefix seems worth the usability trade-off versus 1-byte prefix, especially since it will impact the ability to lookup the transaction on an outside service, which I think a lot of people do to verify their payments. IMO a longer prefix isn't "wasting bytes" anywhere that it really counts. We could save two bytes in the address if we required both pubkeys to start with '03', or save one byte if we required they both start with the same byte, but again doesn't seem worth it (to me) for the arbitrary restriction. The actual internal wallet code for *receiving* STL payments and updating balances is more tricky and probably not something I can personally tackle for bitcoind. Assuming we even want first-class support for generating STL addresses and receiving STL payments in a standard user wallet, someone has to decide if the STL 'd' / 'd2' keys should be... 1) Encrypted as usual, and then keep a list of blocks with interesting transactions, and go through them when the user enters their password? This would cause balances to update differently than how they do now, but perhaps be more secure. 2) Kept unencrypted to allow live scanning as usual? Or keep just 'd2' unencrypted, with some new concept of 'unconfirmed' until the user enters their password to prove they can spend that TX? That kind of extra step seems OK for a merchant but sounds very scary for an average user. 3) Kept encrypted under a separate password? Meh... And last thought for now... At some point, we might want to decide on a convention to highlight these STL addresses as 'reusable' -- but similar questions around revocability remain. I hope we don't need anything like a UTC expiration time baked in to the address. A static PP file will have an expiration date either in the certificate or in 'expires' field, so I think if you want it to expire then use PP? ------------svoj35mbC6KPQXlw6JqQzt Content-Type: multipart/related; boundary=----------svoj35mbC6KPQX57ksPHtp ------------svoj35mbC6KPQX57ksPHtp Content-Type: text/html; charset=iso-8859-15 Content-ID: Content-Transfer-Encoding: Quoted-Printable
You can always just exten= d the payment protocol with the new fields as well, vs making very long = addresses. 

I should have men= tioned that as Task #4. Agree it could be an optional extension and back= ward compatible. I think for displaying the payment in the UI after it's= been made via PP, we have to fully support sending to a new standard ad= dress type anyway. Probably easiest to implement in PP after the address= and transaction building code is done.

So '4a'= would be building a static PP file given the necessary inputs. When I g= et to that point, I'll send out a draft PP extension with fields/formats= if someone else hasn't already. '4b' would be actually adding support f= or parsing those fields and generating the new transaction type into bit= coind.

Any thoughts on the prefix, and one vs t= wo pubkey approach? First of all, do we try to support both equally, or = favor one over the other? I was thinking we could have two different 4 b= yte prefixes but that both render as xSTL/tSTL in Base58 but correspond = to the one vs two pubkeys expected. I think the chance of finding a sing= le prefix which looks like xSTL for both address lengths is 1 in (58^4)^= 2, so that's probably not going to happen.

From= the payer/user perspective, short stealth vs. long stealth is irrelevan= t; they both have the same usability properties from the payer perspecti= ve. So giving them the same Base58 prefix seems like a good plan.
<= div>
The full 4-byte prefix seems worth the usability trad= e-off versus 1-byte prefix, especially since it will impact the ability = to lookup the transaction on an outside service, which I think a lot of = people do to verify their payments. IMO a longer prefix isn't "wasting b= ytes" anywhere that it really counts.

We could = save two bytes in the address if we required both pubkeys to start with = '03', or save one byte if we required they both start with the same byte= , but again doesn't seem worth it (to me) for the arbitrary restriction.=

The actual internal wallet code for *receiving= * STL payments and updating balances is more tricky and probably not som= ething I can personally tackle for bitcoind. Assuming we even want first= -class support for generating STL addresses and receiving STL payments i= n a standard user wallet, someone has to decide if the STL 'd' / 'd2' ke= ys should be...

  1) Encrypted as usual, a= nd then keep a list of blocks with interesting transactions, and go thro= ugh them when the user enters their password?  This would cause bal= ances to update differently than how they do now, but perhaps be more se= cure.

  2) Kept unencrypted to allow live = scanning as usual? Or keep just 'd2' unencrypted, with some new concept = of 'unconfirmed' until the user enters their password to prove they can = spend that TX? That kind of extra step seems OK for a merchant but sound= s very scary for an average user.

  3) Kep= t encrypted under a separate password? Meh...

A= nd last thought for now... At some point, we might want to decide on a c= onvention to highlight these STL addresses as 'reusable' -- but similar = questions around revocability remain. I hope we don't need anything like= a UTC expiration time baked in to the address. A static PP file will ha= ve an expiration date either in the certificate or in 'expires' field, s= o I think if you want it to expire then use PP?
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