Andy Schroder On 02/22/2015 06:06 PM, Eric Voskuil wrote: > On 02/22/2015 02:37 PM, Andy Schroder wrote: >> I'd like to see some discussion too about securing the bluetooth >> connection. Right now it is possible for an eavesdropper to monitor the >> data transferred. > Yes, this should be a prerequisite issue to all others. > >> I'd personally like to see if wrapping the current >> connection with SSL works or if we can run https over a bluetooth >> socket. > There is no reason to add this significant complexity. The purpose of > SSL/TLS is to establish privacy over a *public* channel. But to do so > requires verification by the user of the merchant's public certificate. > Once we rely on the channel being *private*, the entire SSL process is > unnecessary. I guess we need to decide whether we want to consider NFC communication private or not. I don't know that I think it can be. An eavesdropper can place a tiny snooping device near and read the communication. If it is just passive, then the merchant/operator won't realize it's there. So, I don't know if I like your idea (mentioned in your other reply) of putting the session key in the URL is a good idea? > > Presumably we would not want to require PKI for privacy, since that's a > bit of a contradiction. But if one wants to do this NFC is not required, > since the private session can be established over the public (Bluetooth) > network. > >> There was some criticism of this, but I don't think it has been >> tested to know if it is really a problem or not. If we just run https >> over bluetooth, then a lot of my concerns about the message header >> inconsistencies will go away and the connection will also be secure. We >> don't have to reinvent anything. >> >> >> >> Andy Schroder >> >> On 02/22/2015 02:08 PM, Jan Vornberger wrote: >>> Hi everyone, >>> >>> I am working on a Bitcoin point of sale terminal based on a Raspberry >>> Pi, which >>> displays QR codes, but also provides payment requests via NFC. It can >>> optionally >>> receive the sender's transaction via Bluetooth, so if the sender wallet >>> supports it, the sender can be completely offline. Only the terminal >>> needs an >>> internet connection. >>> >>> Typical scenario envisioned: Customer taps their smartphone (or maybe >>> smartwatch >>> in the future) on the NFC pad, confirms the transaction on their phone >>> (or smartwatch) and the transaction completes via Bluetooth and/or the >>> phone's >>> internet connection. >>> >>> You can see a prototype in action here: >>> >>> https://www.youtube.com/watch?v=P7vKHMoapr8 >>> >>> The above demo uses a release version of Schildbach's Bitcoin Wallet, >>> so it >>> works as shown today. However, some parts - especially the Bluetooth >>> stuff - are >>> custom extensions of Schildbach's wallet which are not yet standard. >>> >>> I'm writing this post to document my experience implementing NFC and >>> offline >>> payments and hope to move the discussion forward around standardizing >>> some of >>> this stuff. Andy Schroder's work around his Bitcoin Fluid Dispenser [1,2] >>> follows along the same lines, so his proposed TBIP74 [3] and TBIP75 >>> [4] are >>> relevant here as well. >>> >>> >>> ## NFC vs Bluetooth vs NFC+Bluetooth ## >>> >>> Before I get into the implementation details, a few words for why I >>> decided to >>> go with the combination of NFC and Bluetooth: >>> >>> Doing everything via NFC is an interesting option to keep things >>> simple, but the >>> issue is, that one usually can't maintain the connection while the >>> user confirms >>> the transaction (as they take the device back to press a button or >>> maybe enter a >>> PIN). So there are three options: >>> >>> 1. Do a "double tap": User taps, takes the device back, confirms, then >>> taps >>> again to transmit the transaction. (I think Google Wallet does >>> something like >>> this.) >>> >>> 2. Confirm beforehand: User confirms, then taps and everything can >>> happen in one >>> go. The disadvantage is, that you confirm the transaction before you >>> have seen >>> the details. (I believe Google Wallet can also work this way.) >>> >>> 3. Tap the phone, then establish a Bluetooth connection which allows >>> you to do >>> all necessary communication even if the user takes the device back. >>> >>> I feel that option 3 is the nicest UX, so that is what I am focusing >>> on right >>> now, but there are pros and cons to all options. One disadvantage of >>> option 3 in >>> practice is, that many users - in my experience - have Bluetooth >>> turned off, so >>> it can result in additional UI dialogs popping up, asking the user to >>> turn on >>> Bluetooth. >>> >>> Regarding doing everything via Bluetooth or maybe BLE: I have been >>> following the >>> work that Airbitz has done around that, but personally I prefer the NFC >>> interaction of "I touch what I want to pay" rather than "a payment >>> request comes >>> to me through the air and I figure out whether it is meant for me/is >>> legitimate". >>> >>> >>> ## NFC data formats ## >>> >>> A bit of background for those who are not that familiar with NFC: Most >>> Bitcoin >>> wallets with NFC support make use of NDEF (NFC Data Exchange Format) >>> as far as I >>> am aware (with CoinBlesk being an exception, which uses host-based card >>> emulation, if I understand it correctly). NDEF defines a number of >>> record types, >>> among them 'URI' and 'Mime Type'. >>> >>> A common way of using NFC with Bitcoin is to create a URI record that >>> contains a >>> Bitcoin URI. Beyond that Schildbach's wallet (and maybe others?) also >>> support >>> the mime type record, which is then set to >>> 'application/bitcoin-paymentrequest' >>> and the rest of the NFC data is a complete BIP70 payment request. >>> >>> >>> ## Implementation ## >>> >>> To structure the discussion a little bit, I have listed a number of >>> scenarios to >>> consider below. Not every possible combination is listed, but it >>> should cover a >>> bit of everything. >>> >>> Scenarios: >>> >>> 1) Scan QR code, transmit transaction via Bitcoin network >>> Example QR code: bitcoin:1asdf...?amount=42 >>> >>> 2) Touch NFC pad, transmit transaction via Bitcoin network >>> Example NFC URI: bitcoin:1asdf...?amount=42 >>> >>> 3) Scan QR code, fetch BIP70 details via HTTP, post transaction via HTTP >>> Example QR code: >>> bitcoin:1asdf...?amount=42&r=https://example.org/bip70paymentrequest >>> >>> 4) Touch NFC pad, fetch BIP70 details via HTTP, post transaction via HTTP >>> Example NFC URI: >>> bitcoin:1asdf...?amount=42&r=https://example.org/bip70paymentrequest >>> >>> 5) Touch NFC pad, receive BIP70 details directly, post transaction via >>> HTTP >>> Example NFC MIME record: application/bitcoin-paymentrequest + >>> BIP70 payment request >>> >>> 6) Scan QR code, fetch BIP70 details via Bluetooth, post transaction >>> via Bluetooth >>> Example QR code: bitcoin:1asdf...?amount=42&bt=1234567890AB >>> Payment request has 'payment_url' set to 'bt:1234567890AB' >>> >>> 7) Touch NFC pad, fetch BIP70 details via Bluetooth, post transaction >>> via Bluetooth >>> Example NFC URI: bitcoin:1asdf...?amount=42&bt=1234567890AB >>> Payment request has 'payment_url' set to 'bt:1234567890AB' >>> >>> Scenarios 1 and 2 are basically the 'legacy'/pre-BIP70 approach and I >>> am just >>> listing them here for comparison. Scenario 3 is what is often in use >>> now, for >>> example when using a checkout screen by BitPay or Coinbase. >>> >>> I played around with both scenarios 4 and 5, trying to decide whether >>> I should >>> use an NFC URI record or already provide the complete BIP70 payment >>> request via >>> NFC. >>> >>> My experience here has been, that the latter was fairly fragile in my >>> setup >>> (Raspberry Pi, NFC dongle from a company called Sensor ID, using >>> nfcpy). I tried >>> with signed payment requests that were around 4k to 5k and the >>> transfer would >>> often not complete if I didn't hold the phone perfectly in place. So I >>> quickly >>> switched to using the NFC URI record instead and have the phone fetch >>> the BIP70 >>> payment request via Bluetooth afterwards. Using this approach the >>> amount of data >>> is small enough that it's usually 'all or nothing' and that seems more >>> robust to >>> me. >>> >>> That said, I continue to have problems with the NFC stack that I'm >>> using, so it >>> might just be my NFC setup that is causing these problems. I will >>> probably give >>> the NXP NFC library a try next (which I believe is also the stack that >>> is used >>> by Android). Maybe I have more luck with that approach and could then >>> switch to >>> scenario 5. >>> >>> Scenarios 6 and 7 is what the terminal is doing right now. The 'bt' >>> parameter is >>> the non-standard extension of Andreas' wallet that I was mentioning. >>> TBIP75 >>> proposes to change 'bt' into 'r1' as part of a more generic approach of >>> numbering different sources for the BIP70 payment request. I think >>> that is a >>> good idea and would express my vote for this proposal. So the QR code >>> or NFC URI >>> would then look something like this: >>> >>> >>> bitcoin:1asdf...?amount=42&r=https://example.org/bip70&r1=bt:1234567890AB/resource >>> >>> >>> In addition the payment request would need to list additional >>> 'payment_url's. My >>> proposal would be to do something like this: >>> >>> message PaymentDetails { >>> ... >>> optional string payment_url = 6; >>> optional bytes merchant_data = 7; >>> repeated string additional_payment_urls = 8; >>> // ^-- new; to hold things like 'bt:1234567890AB' >>> } >>> >>> TBIP75 proposes to just change 'optional string payment_url' into >>> 'repeated >>> string payment_url'. If this isn't causing any problems (and hopefully >>> not too >>> much confusion?) I guess that would be fine too. >>> >>> In my opinion a wallet should then actually attempt all or multiple of >>> the >>> provided mechanisms in parallel (e.g. try to fetch the BIP70 payment >>> request via >>> both HTTP and Bluetooth) and go with whatever completes first. But >>> that is of >>> course up to each wallet to decide how to handle. >>> >>> TBIP75 furthermore proposes to include an additional 'h' parameter >>> which would >>> be a hash of the BIP70 payment request, preventing a MITM attack on the >>> Bluetooth channel even if the BIP70 payment request isn't signed. This >>> would >>> have also been my suggestion, although I know that Mike Hearn has raised >>> concerns about this approach. One being, that one needs to finalize >>> the BIP70 >>> payment request at the time the QR code and NFC URI is generated. >>> >>> >>> ## Questions ## >>> >>> My questions to the list: >>> >>> 1) Do you prefer changing 'optional string payment_url' into 'repeated >>> string >>> payment_url' or would you rather introduce a new field >>> 'additional_payment_urls'? >>> >>> 2) @Andreas: Is the r, r1, r2 mechanism already implemented in Bitcoin >>> Wallet? >>> >>> 3) Are there other comments regarding 'h' parameter as per TBIP75? >>> >>> 4) General comments, advice, feedback? >>> >>> I appreciate your input! :-) >>> >>> Cheers, >>> Jan >>> >>> [1] http://andyschroder.com/BitcoinFluidDispenser/ >>> [2] >>> https://www.mail-archive.com/bitcoin-development%40lists.sourceforge.net/msg06354.html >>> >>> [3] https://github.com/AndySchroder/bips/blob/master/tbip-0074.mediawiki >>> [4] https://github.com/AndySchroder/bips/blob/master/tbip-0075.mediawiki >>> >>> ------------------------------------------------------------------------------ >>> >>> Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server >>> from Actuate! Instantly Supercharge Your Business Reports and Dashboards >>> with Interactivity, Sharing, Native Excel Exports, App Integration & more >>> Get technology previously reserved for billion-dollar corporations, FREE >>> http://pubads.g.doubleclick.net/gampad/clk?id=190641631&iu=/4140/ostg.clktrk >>> >>> _______________________________________________ >>> Bitcoin-development mailing list >>> Bitcoin-development@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/bitcoin-development >>> >>> >>> >> >> >> ------------------------------------------------------------------------------ >> Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server >> from Actuate! Instantly Supercharge Your Business Reports and Dashboards >> with Interactivity, Sharing, Native Excel Exports, App Integration & more >> Get technology previously reserved for billion-dollar corporations, FREE >> http://pubads.g.doubleclick.net/gampad/clk?id=190641631&iu=/4140/ostg.clktrk >> >> >> >> _______________________________________________ >> Bitcoin-development mailing list >> Bitcoin-development@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/bitcoin-development >>