Our BIP just defines protocol definitions, and doesn't really dictate how people use them (we're coming up with a new title for the BIP, by the way, to more accurately convey that). Using our definitions as building blocks, someone could definitely accomplish what you described. For example, Joe Mobile Wallet User's wallet could upload a slew of generic PaymentRequest messages with signatures to prove his identity, and the server could then create encryptedPaymentRequest messages using the server's key for encryption and communication with the other party. In this case the server would essentially be a proxy for the user without having actual access to the user's private keys.

My personal goal with the protocol was to keep it extremely flexible so developers could use it to build all different types of schemes while keeping standard messages that could be forwarded between services if needed. Does the above make sense?

James

On Tue, Mar 8, 2016 at 2:55 PM Luke Dashjr via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:

Is there a way for Joe Mobile Wallet User to upload a set of N PaymentRequests
authenticated by his key to an untrusted server, which encrypts and passes
them on in response to InvoiceRequests? Or does this necessarily require the
recipient to be online?

On Tuesday, March 01, 2016 6:58:16 PM Justin Newton via bitcoin-dev wrote:
> The following draft BIP proposes an update to the Payment Protocol.
>
> Motivation:
>
> The motivation for defining this extension to the BIP70 Payment Protocol is
> to allow 2 parties to exchange payment information in a permissioned and
> encrypted way such that wallet address communication can become a more
> automated process. Additionally, this extension allows for the requestor of
> a PaymentRequest to supply a certificate and signature in order to
> facilitate identification for address release. This also allows
> for automated creation of off blockchain transaction logs that are human
> readable, containing who you transacted with, in addition to the
> information that it contains today.
>
> The motivation for this extension to BIP70 is threefold:
>
> 1. Ensure that the payment details can only be seen by the participants in
> the transaction, and not by any third party.
> 2. Enhance the Payment Protocol to allow for store and forward servers in
> order to allow, for example, mobile wallets to sign and serve
> Payment Requests.
> 3. Allow a sender of funds the option of sharing their identity with the
> receiver. This information could then be used to:
>
> * Make bitcoin logs more human readable
> * Give the user the ability to decide who to release payment
> details to
> * Allow an entity such as a political campaign to ensure donors
> match regulatory and legal requirements
> * Allow for an open standards based way for regulated financial
> entities to meet regulatory requirements
> * Automate the active exchange of payment addresses, so static
> addresses and BIP32 X-Pubs can be avoided to maintain privacy
> and convenience
>
> In short we wanted to make bitcoin more human, while at the same time
> improving transaction privacy.
>
> Full proposal here:
>
> https://github.com/techguy613/bips/blob/master/bip-invoicerequest-extension
> .mediawiki
>
> We look forward to your thoughts and feedback on this proposal!
>
> Justin
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