I agree we need a payment protocol, but instead of thinking of all of the
things we might possibly want I would like to solve a few boring problems
that we have right now.

Absolutely critical:

+ Bitcoin addresses by themselves are insecure against man-in-the-middle
attacks. We need a payment protocol so if you get a donation link for
"Bitcoin Foundation" in an email message and click on it you can be
reasonably certain that your coins will actually go to the Foundation and
not some hacker at your ISP that modified the email message.

+ After sending payment I should have a receipt that proves I followed the
payee's instructions, so if the payee says they never received the funds I
can prove that it wasn't my fault.

+ Protocol for gathering signatures from multiple devices
(extension/variation of the basic payment protocol, I think).

Not absolutely necessary, but I think v1 should have it anyway:

+ Where-to-send-refund information included with payments, so
overpayments/refunds can be handled efficiently and displayed intelligently
in the customer's wallet.


Everything else I think can wait.

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Gavin Andresen