P4 aims to solve the problem of subscription services offering end-to-end private cryptocurrency payments. This protocol introduces periodicity to cryptocurrency payments through an ongoing relationship between the merchant and the customer without unintentionally disclosing personally identifiable information. We are creating this protocol to allow us to offer a truely end-to-end private subscription data storage solution built with Tahoe-LAFS. By sharing it, we hope that other subscription services will implement our protocol and further the adoption of cryptocurrency payments in real world retail use cases.

Although this protocol is currently a work in progress, we have already specified some design decisions. For periodicity, we are avoiding a payment pre-authorization design to keep the user in control of their keys. And for privacy we are utilizing Zcash shielded transactions and the coming improvements in the Sapling release.This protocol is being created by the Least Authority team with support from the Zcash team.