[Bitcoin-development] Bill Request Message - (another) Proposed BIP 70 extension

[Paul Goldstein <paul@realfoot.com>]

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Here's an idea for a BIP 70 extension to let wallets be scanned by merchant
bar code readers to start off a payment request flow instead of the other
way around (wallet scanning the merchant QR). Useful for brick and mortar
merchants and mobile wallet apps.


Motivation:
A mechanism is needed for mobile wallets to request a bill, so that a
payment protocol flow can be initiated. Current mechanisms for initiating
BIP70 payment flows generally require wallets to either scan a merchant
barcode (not optimal, see below), or click on a specially formatted url
link (only suitable while browsing and purchasing on a merchant website).

Successful non-bitcoin mobile wallet apps to date (a popular coffee shop
app comes to mind) allow for the wallet app to be scanned by the merchant
and not the other way around (as is commonly done in bitcoin wallets
today). For broad bitcoin adoption we need a mechanism for wallets to be
scanned by merchant bar code readers at brick and mortar shops. This will
also greatly ease checkouts at drive throughs and allows merchants to
leverage existing hardware (barcode readers).

Other technologies like NFC may obviate the need for this extension,
however, those technologies remain somewhat uncommon and may not be
suitable for smaller wearables hitting the market.

message BillRequest {
 required uint64 time = 1;
 optional uint64 expires = 2;
 required string bill_request_uri = 3;
}


time - Unix timestamp (seconds since 1-Jan-1970 UTC) when the BillRequest
was created.
expires - Unix timestamp (UTC) after which the BillRequest should be
considered invalid (wallets may only be monitoring for messages for a short
time).
bill_req_addr - Typically a URL where a BIP70 payment request can be sent
that is being monitored by the wallet. However this could also support URIs
like "sms:860-555-1212" or "mailto:asdf@gmail.com" allowing for a variety
of connection options.

Recommendations: it is recommended that wallet apps display a non-QR
barcode like a PDF417 barcode to initiate the Bill Request flow. This will
avoid confusion with existing QR code usage in wallet apps.

--------
Paul G.

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