1. Introduction

1. Introduction

The Web Push protocol [RFC8030] is an intermediated protocol by necessity. Messages from an application server are delivered to a user agent (UA) via a push service, as shown in Figure 1.

+-------+           +--------------+       +-------------+
|  UA   |           | Push Service |       | Application |
+-------+           +--------------+       +-------------+
    |                      |                      |
    |        Setup         |                      |
    |<====================>|                      |
    |           Provide Subscription              |
    |-------------------------------------------->|
    |                      |                      |
    :                      :                      :
    |                      |     Push Message     |
    |    Push Message      |<---------------------|
    |<---------------------|                      |
    |                      |                      |

                             Figure 1

This document describes how messages sent using this protocol can be secured against inspection, modification, and forgery by a push service.

Web Push messages are the payload of an HTTP message [RFC7230]. These messages are encrypted using an encrypted content encoding [RFC8188]. This document describes how this content encoding is applied and describes a recommended key management scheme.

Multiple users of Web Push at the same user agent often share a central agent that aggregates push functionality. This agent can enforce the use of this encryption scheme by applications that use push messaging. An agent that only delivers messages that are properly encrypted strongly encourages the end-to-end protection of messages.

A web browser that implements the Push API [API] can enforce the use of encryption by forwarding only those messages that were properly encrypted.

1.1. Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

This document uses the terminology from [RFC8030], primarily "user agent", "push service", and "application server".