I think the right approach for this is to actually implement it and then propose a BIP. There are so many possible features we could add to the payment protocol, any other approach would rapidly turn into lots of people deciding to do the "fun bits" and often leaving others doing the hard work with difficult or unworkable specs.

For instance, if you try to implement this, you would rapidly discover that it probably makes more sense to do this as an additional set of fields in PaymentDetails rather than a new message type entirely. A new top level message type would in turn require new MIME types, URI extensions and so on. That doesn't make any sense.

Once you decide to extend PaymentDetails, the next discovery would be that it probably makes sense to try and solve the problem of address re-use for recurring payments first, before speccing out time intervals and so on. That's a separate BIP.

I'm all for adding recurring payments as a feature, that's what the protocol is there for. But I'd like to see future protocol extension requests come after at least one working implementation has been made .....

On Tue, Jan 28, 2014 at 3:36 AM, Stephane Brossier <stephane@kill-bill.org> wrote:

Hi,

[I sent this email 2 days ago prior my registration to the mailing list; please forgive me if this is a duplicate]

I would like to propose an extension to the Payment Protocol (bip-0070) to address the case of recurring payments in Bitcoin -- new bip or modification of bip-0070.

There has been a lot of growth in the last few years in the 'subscription economy' with many new companies embracing that model -- online video, gaming, groceries, newspapers,... In parallel, Bitcoin is growing into a mainstream currency (hence bip-0070), and so the next logical step would be to define a protocol to address that need.

We have been working in the past few years on an open-source billing platform (http://kill-bill.org/), and recently came with a prototype to do recurring billing in Bitcoin (see http://thekillbillstory.wordpress.com/2014/01/20/bitcoin-plugin/ and http://thekillbillstory.wordpress.com/2014/01/11/coinbase-integration-experiment/).

The work flow would look similar to the one from bip-0070. There would need to be some additions; the flow could be summarized as follow:

0. Click: 'Subscribe Now'

1. Wallet would get a RecurringPaymentRequestAuth which describes the nature of the future recurring payments
2. The Customer would get prompted from the wallet to authorize it.
3. The wallet would then poll the Merchant server (startup time, and/or well defined frequency) and potentially merchant would start issuing a PaymentRequest); the role of the wallet is to ensure that PaymentRequest is within the bounds of what was accepted by the customer-- amount, frequency,.. If it is, then it would make the Payment the same way it works for bip-0070

Is that something that the community would be interested in? We could provide more details about the protocol we have in mind (messages and flow), and also provide an implementation with bitcoinj as a wallet and Kill Bill as a merchant server.

Le me know what you think.

Stéphane

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