With the recent discussion started today regarding another bluetooth communication proposal created by Airbitz, I'd like to bring people's attention back to this proposal that saw little discussion last fall. I guess I'm not sure why two proposals are being created. Is their some advantage of using bluetooth low energy over standard bluetooth (I'm not well versed in bluetooth low energy)? This NFC coupled approach seems to avoid a lot of issues with identifying the correct payee. You can see this proposed scheme demonstrated in action in a POS application in the video link below which demonstrates it with my fuel pump and Andreas Schildbach's wallet.

There was a small discussion that occurred after my original announcement below. If you are new to this e-mail list, you can find an archive of those few replies here: https://www.mail-archive.com/bitcoin-development%40lists.sourceforge.net/msg06354.html

Since this original announcement, a few improvements have been made to the proposal:

1. Improved documentation and explanation of the use cases in
   Schildbach's wallet's wiki
    1. https://github.com/schildbach/bitcoin-wallet/wiki/Payment-Requests
2. Issue with the payment_url field has resolved by changing to a
   repeated field and requiring the wallet to search for the protocol
   they want to use, rather than expecting it to be a certain element
   number in the list.
    1. https://github.com/AndySchroder/bips/blob/master/tbip-0075.mediawiki

Although there are some interesting use cases of Airbitz's proposal's work flow, tapping an NFC radio with a 5 mm range requires much less brain power and time than picking the correct name on the app's screen. The manual name picking is going to be especially crazy in a very congested location. The payer isn't ever going to want to have to try and figure out what register or payment terminal they are at for most applications I would ever use.

I'd like to see something happen with this technology. I've also noticed that micropayment channels have little formality to being established practically and it would be awesome if they could be managed over bluetooth as well. Maybe more improvements to the payment protocol can simultaneously result (and also extended to bluetooth) that embrace the establishment of micropayment channels.

Andy Schroder

On 10/17/2014 03:58 PM, Andy Schroder wrote:

I'd like to introduce two proposed BIPs. They are primarily focused on implementing the payment protocol using bluetooth connections. I've been working on automated point of sale devices and bluetooth communication is critical in my mind due to the potential lack of internet access at many points of sale, either due to lack of cellular internet coverage, lack of payee providing wireless internet, and/or due to financial constraints of the payer prohibiting them from maintaining a cellular internet service plan. These BIPs are largely modeled after the current functionality of Andreas Schildbach's android Bitcoin Wallet's bluetooth capability. I've discussed the communication scheme with him in depth and believe these proposals to clearly and accurately represent the communication scheme.

There is also an additional &h= parameter added to the bitcoin: URI scheme which applies to both bluetooth and http payment protocol requests which allows for a hash of the payment request to be included. This hash was proposed by Andreas as an amendment to BIP72, but others preferred not to amend BIP72 since it has already been put into place. The current version of Schildbach's bitcoin wallet already supports the "h parameter".

I'd appreciate feedback from everyone, particularly wallet developers as widespread bluetooth support among wallets is very important to me. I'm also very new to this mailing list as well as the BIP writing process, so I'd appreciate your understanding if my conventions are not standard. I am currently using the naming conventions "TBIP", so that I can propose /temporary/ BIP numbers, and cross reference between the two. Obviously these will change if the BIPs are formally adopted. You can find a copy of these proposed BIPs at the following links:

  * https://github.com/AndySchroder/bips/blob/master/tbip-0074.mediawiki
  * https://github.com/AndySchroder/bips/blob/master/tbip-0075.mediawiki

If you are interested, you can see a demonstration of many of the proposed features using Schildbach's wallet and my fuel pump in a video I recently created: https://youtu.be/kkVAhA75k1Y . The main thing not implemented is multiple URLs for the payment protocol, so, as a hack, I'm just presenting https vi QR code and bluetooth via NFC on my fuel pump for now.

There are a few known issues that could be improved to this bluetooth communication scheme as well as the general payment protocol and myself and Andreas would like to receive feedback regarding concerns and potential solutions. Some of the known issues are:

  * There may seem to be some inconsistency in the connection header
    messages between the payment request connection and the payment
    connection. This is largely because it is how Andreas originally
    implemented the communication and is hesitant to change it since
    there are many instances of is software already deployed that
    implement this scheme.
  * The current method uses an unauthenticated bluetooth connection
    for bluetooth 2.1 and newer devices (subject to man in the middle
    attacks, but not passive eavesdroppers), and an unsecure and
    unauthenticated connection for older devices. The known concerns
    here are that someone within 100 meters of the payer could track
    the bitcoin addresses used for the transaction and could possibly
    replace the refund address by submitting a forged payment message
    to the payee. Requiring bluetooth 2.1 and authenticating the
    connection out of band unfortunately don't seem to be as
    straightforward/simple of a task with most bluetooth libraries
    (although I'd love for someone to prove me wrong). It's possible
    this communication scheme could be extended to use an https "like"
    protocol that would not care if the underlying bluetooth
    connection is authenticated or encrypted. It's actually possible
    that http over a bluetooth socket (instead of tcp socket) could be
    implemented, however it is presently uncertain whether this would
    be too slow, too much overhead (both on the devices software and
    communication), or if http could easily be run over bluetooth
    sockets on all platforms.
  * There is no acknowledgement failure message possible in the
    payment protocol, only an acknowledgement message or lack of
    acknowledgement message. This issue seems to be a concern and as a
    result, the memo field is used to send an "ack" or "nack" in
    Schildbach's wallet. Can we add a boolean status field to the
    payment acknowledgement message?
  * I'd personally like a new optional boolean field added to the
    "PaymentDetails" portion of the "PaymentRequest" to allow for the
    payer's wallet to match the "Output" optional "amount" fields as a
    total amount of all Outputs, rather than requiring the amount for
    each output to be matched exactly. As it currently is, the payee
    can specify multiple receiving addresses in order to require a
    payer split up the payments so that when the payee then goes to
    spend the funds later, they don't necessarily have to give their
    payees as much knowledge of their balances and spending and
    receiving habits and sources. As the payment protocol currently is
    requiring all output amounts to be matched exactly for each
    output, there is no flexibility given to the payer in order to
    reduce a merging or unnecessary diverging of account funds, which
    can reduce the privacy of both the payer and the payee. If the
    payee were given the option to allow the payer the option to
    divide the amounts amount the outputs intelligently, there can be
    some privacy gained.
  * Amount of data stored in QR codes may be getting large when a
    backwards compatible URL is used (for wallets that don't support
    the payment protocol) and can be difficult to scan with outdoor
    screens that have an extra weather resistant pane when in direct
  * The number of offline transactions of a wallet is limited to the
    known unspent outputs when they go offline. Long term, I'd like to
    see wallet devices that can use systems such as Kryptoradio's
    DVB-T based broadcast (but this will need yet another radio!).
    Another project may be to develop a blockchain query protocol of
    some kind where retailers can provide access to blockchain data so
    that customer's wallets can update their known unspent outputs via
    bluetooth. It's possible such a bluetooth system could be used in
    combination of "Kryptoradio" like broadcasts to provide multiple
    blockchain references.
  * The additional payment_url approach is a bit sloppy of a solution
    in the PaymentDetails portion of the PaymentRequest. It would have
    been ideal to just change this from an optional field to a
    repeated field, however, the backwards compatibility in the
    protocol buffer format will provide the last item in the array for
    a repeated field (to a code that expects it to be an optional
    field), rather than the first. Because of this, backwards
    compatibility with https payment requests wouldn't work if the
    payment_url field is just changed to a repeated field.
      o Possible alternatives to what is described in the proposed BIP
          + Change payment_url to a repeated field and then reverse
            the order of the parameter numbers in the payment_url,
            compared to the bitcoin URL "r parameter".
          + Create an additional, new payment_url_multi repeated field
            (or some better name), and then leave the original
            payment_url field in there for backwards compatibility
            (and then maybe phase it out in the future).
      o Reference
          + https://developers.google.com/protocol-buffers/docs/proto#updating
              # "|optional| is compatible with |repeated|. Given
                serialized data of a repeated field as input, clients
                that expect this field to be |optional| will take the
                last input value if it's a primitive type field or
                merge all input elements if it's a message type field."

Your comments and suggestions would be greatly appreciated.

Andy Schroder

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