572 lines
25 KiB
Markdown
572 lines
25 KiB
Markdown
---
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title: 71/STATUS-PUSH-NOTIFICATION-SERVER
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name: Push Notification Server
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status: draft
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category: Standards Track
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description: A set of methods to allow Status clients to use push notification services in mobile environments.
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editor: Jimmy Debe <jimmy@status.im>
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contributors:
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- Andrea Maria Piana <andreap@status.im>
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---
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- Status: draft
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- Category: Standards Track
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- Editor: Jimmy Debe <jimmy@status.im>
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- Contributors:
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- Andrea Maria Piana <andreap@status.im>
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## Abstract
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A push notification server implementation for IOS devices and Android devices.
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This specification provides a set of methods that allow clients to use push notification services in mobile environments.
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## Background
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Push notification for iOS and Android devices can only be implemented by relying on
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[APN](https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/APNSOverview.html#//apple_ref/doc/uid/TP40008194-CH8-SW1),
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Apple Push Notification, service for iOS or
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[Firebase](https://firebase.google.com/) for Android.
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For some Android devices, foreground services are restricted, requiring a user to grant authorization to applications to use foreground notifications.
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Apple iOS devices restrict notifications to a few internal functions that every application can not use.
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Applications on iOS can request execution time when they are in the background. This has a limited set of use cases for example,
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it will not schedule any time if the application was closed with force quit.
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Requesting execution time is not responsive enough to implement a push notification system.
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Status provides a set of methods to acheive push notification services.
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Since this can not be safely implemented in a privacy-preserving manner, clients need to be given an option to opt-in to receive and send push notifications.
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They are disabled by default.
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## Specification
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The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [2119](https://www.ietf.org/rfc/rfc2119.txt).
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### Definitions
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| Terminology | Description |
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| --------------- | --------- |
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| client | A node that implements the Status specifications. |
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| user | The owner of a device that runs a client. |
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| server | A service that performs push notifications. |
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| Waku-Store | A Waku node that decides to provide functionality to store messages permanently and deliver the messages to requesting clients. As described in [13/WAKU-STORE](../../waku/standards/core/13/store) specification.|
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### Server Components
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| Components | Description |
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| --------------- | --------- |
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| gorush Instance | Only used by push notification servers and MUST be publicly available.|
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| Push Notification Server | Used by clients to register for receiving and sending notifications. |
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| Registering Client | A client that wants to receive push notifications. |
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| Sending Client | A client that wants to send push notifications. |
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### Requirements:
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The party releasing the app MUST possess a certificate for the Apple Push Notification service and it MUST run a
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[gorush](https://github.com/appleboy/gorush) publicly accessible server for sending the actual notification.
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The party releasing the app MUST run its own [gorush](https://github.com/appleboy/gorush).
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### Push Notification Server Flow
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#### Registration Process:
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#### Sending and Receiving Notification Process:
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### Registering Client
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Registering a client with a push notification service.
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- A client MAY register with one or more push notification services in order to increase availability.
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- A client SHOULD make sure that all the notification services they registered with have the same information about their tokens.
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- A `PNR message` (Push Notification Registration) MUST be sent to the
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[partitioned topic](../../waku/standards/application/54/x3dh-sessions) for the public key of the node, encrypted with this key.
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- The message MUST be wrapped in a [`ApplicationMetadataMessage`](../62/payloads) with type set to `PUSH_NOTIFICATION_REGISTRATION`.
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- The marshaled protobuf payload MUST also be encrypted with AES-GCM using the Diffie–Hellman key generated from the client and server identity.
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This is done in order to ensure that the extracted key from the signature will be considered invalid if it can’t decrypt the payload.
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The content of the message MUST contain the following [protobuf record](https://developers.google.com/protocol-buffers/):
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```protobuf
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message PushNotificationRegistration {
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enum TokenType {
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UNKNOWN_TOKEN_TYPE = 0;
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APN_TOKEN = 1;
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FIREBASE_TOKEN = 2;
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}
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TokenType token_type = 1;
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string device_token = 2;
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string installation_id = 3;
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string access_token = 4;
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bool enabled = 5;
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uint64 version = 6;
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repeated bytes allowed_key_list = 7;
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repeated bytes blocked_chat_list = 8;
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bool unregister = 9;
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bytes grant = 10;
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bool allow_from_contacts_only = 11;
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string apn_topic = 12;
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bool block_mentions = 13;
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repeated bytes allowed_mentions_chat_list = 14;
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}
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```
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A push notification server will handle the message according to the following rules:
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- it MUST extract the public key of the sender from the signature and verify that the payload can be decrypted successfully.
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- it MUST verify that `token_type` is supported.
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- it MUST verify that `device_token` is non empty.
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- it MUST verify that `installation_id` is non empty.
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- it MUST verify that `version` is non-zero and greater than the currently stored version for the public key and `installation_id` of the sender, if any.
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- it MUST verify that `grant` is non empty and according to the Grant Server specs.
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- it MUST verify that `access_token` is a valid uuid.
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- it MUST verify that `apn_topic` is set if token_type is APN_TOKEN.
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- The message MUST be wrapped in a [`ApplicationMetadataMessage`](../62/payloads) with type set to `PUSH_NOTIFICATION_REGISTRATION_RESPONSE`.
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The payload of the response is:
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```protobuf
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message PushNotificationRegistrationResponse {
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bool success = 1;
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ErrorType error = 2;
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bytes request_id = 3;
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enum ErrorType {
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UNKNOWN_ERROR_TYPE = 0;
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MALFORMED_MESSAGE = 1;
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VERSION_MISMATCH = 2;
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UNSUPPORTED_TOKEN_TYPE = 3;
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INTERNAL_ERROR = 4;
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}
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}
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```
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A client SHOULD listen for a response sent on the [partitioned topic](../../waku/standards/application/54/x3dh-sessions) that the key used to register.
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If success is true the client has registered successfully.
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If `success` is `false`:
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> If `MALFORMED_MESSAGE` is returned, the request SHOULD NOT be retried without ensuring that it is correctly formed.
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> If `INTERNAL_ERROR` is returned, the request MAY be retried, but the client MUST backoff exponentially.
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#### Handle Errors:
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- If the message can’t be decrypted, the message MUST be discarded.
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- If `token_type` is not supported, a response MUST be sent with `error` set to `UNSUPPORTED_TOKEN_TYPE`.
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- If `token`, `installation_id`, `device_tokens`, `version` are empty, a response MUST be sent with `error` set to `MALFORMED_MESSAGE`.
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- If the `version` is equal or less than the currently stored `version`, a response MUST be sent with `error` set to `VERSION_MISMATCH`.
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- If any other error occurs the `error` SHOULD be set to `INTERNAL_ERROR`.
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- If the response is successful `success` MUST be set to `true` otherwise a response MUST be sent with `success` set to `false`.
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- `request_id` SHOULD be set to the [`SHAKE-256`](https://nvlpubs.nist.gov/nistpubs/fips/nist.fips.202.pdf) of the encrypted payload.
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- The response MUST be sent on the [partitioned topic](../../waku/standards/application/54/x3dh-sessions) of the sender and
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MUST not be encrypted using the secure transport to facilitate the usage of ephemeral keys.
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- If no response is returned, the request SHOULD be considered failed and
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MAY be retried with the same server or a different one, but clients
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MUST exponentially backoff after each trial.
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## Push Notification Server
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A node that handles receiving and sending push notifications for clients.
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### Query Topic:
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On successful registration the server MUST be listening to the topic derived from:
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> `0x` + HexEncode(Shake256(CompressedClientPublicKey))
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Using the topic derivation algorithm described here and listen for client queries.
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#### Server Grant:
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A client MUST authorize a push notification server to send them push notifications.
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This is done by building a grant which is specific to a given client-server pair.
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When receiving a grant, the server MUST validate that the signature matches the registering client.
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The grant is built as:<br />
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`Signature(Keccak256(CompressedPublicKeyOfClient . CompressedPublicKeyOfServer . AccessToken), PrivateKeyOfClient)`
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#### Unregistering with a Server:
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- To unregister a client MUST send a `PushNotificationRegistration` request as described above with `unregister` set
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to `true`, or removing their device information.
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- The server MUST remove all data about this user if `unregistering` is `true`, apart from the `hash` of the public key and
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the `version` of the last options, in order to make sure that old messages are not processed.
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- A client MAY unregister from a server on explicit logout if multiple chat keys are used on a single device.
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#### Re-registering with a Server:
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- A client SHOULD re-register with the node if the APN or FIREBASE token changes.
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- When re-registering a client SHOULD ensure that it has the most up-to-date `PushNotificationRegistration` and
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increment `version` if necessary.
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- Once re-registered, a client SHOULD advertise the changes.
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Changing options is handled the same as re-registering.
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#### Advertising a Server:
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Each user registered with one or more push notification servers
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SHOULD advertise periodically the push notification services they have registered with for each device they own.
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```protobuf
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message PushNotificationQueryInfo {
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string access_token = 1;
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string installation_id = 2;
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bytes public_key = 3;
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repeated bytes allowed_user_list = 4;
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bytes grant = 5;
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uint64 version = 6;
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bytes server_public_key = 7;
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}
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message ContactCodeAdvertisement {
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repeated PushNotificationQueryInfo push_notification_info = 1;
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}
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```
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#### Handle Advertisement Message:
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- The message MUST be wrapped in a [`ApplicationMetadataMessage`](../62/payloads) with type set to `PUSH_NOTIFICATION_QUERY_INFO`.
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- If no filtering is done based on public keys, the access token SHOULD be included in the advertisement.
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Otherwise it SHOULD be left empty.
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- This SHOULD be advertised on the [contact code topic](../../waku/standards/application/53/x3dh) and
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SHOULD be coupled with normal contact-code advertisement.
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- When a user register or re-register with a push notification service, their contact-code SHOULD be re-advertised.
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- Multiple servers MAY be advertised for the same installation_id for redundancy reasons.
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#### Discovering a Server:
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To discover a push notification service for a given user, their
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[contact code topic](../../waku/standards/application/53/x3dh) SHOULD be listened to.
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A Waku-Store node can be queried for the specific topic to retrieve the most up-to-date contact code.
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#### Querying a Server:
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If a token is not present in the latest advertisement for a user, the server SHOULD be queried directly.
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To query a server a message:
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```protobuf
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message PushNotificationQuery {
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repeated bytes public_keys = 1;
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}
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```
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#### Handle Query Message:
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- The message MUST be wrapped in a [`ApplicationMetadataMessage`](../62/payloads) with type set to `PUSH_NOTIFICATION_QUERY`.
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- it MUST be sent to the server on the topic derived from the hashed public key of the key we are querying,
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[as described above](#query-topic).
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- An ephemeral key SHOULD be used and SHOULD NOT be encrypted using the [secure transport](../../waku/standards/application/53/x3dh).
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If the server has information about the client a response MUST be sent:
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```protobuf
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message PushNotificationQueryInfo {
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string access_token = 1;
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string installation_id = 2;
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bytes public_key = 3;
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repeated bytes allowed_user_list = 4;
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bytes grant = 5;
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uint64 version = 6;
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bytes server_public_key = 7;
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}
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message PushNotificationQueryResponse {
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repeated PushNotificationQueryInfo info = 1;
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bytes message_id = 2;
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bool success = 3;
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}
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```
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#### Handle Query Response:
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- A `PushNotificationQueryResponse` message MUST be wrapped in a
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[`ApplicationMetadataMessage`](../62/payloads) with type set to `PUSH_NOTIFICATION_QUERY_RESPONSE`.
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Otherwise a response MUST NOT be sent.
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- If `allowed_key_list` is not set `access_token` MUST be set and `allowed_key_list` MUST NOT be set.
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- If `allowed_key_list` is set `allowed_key_list` MUST be set and `access_token` MUST NOT be set.
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- If `access_token` is returned, the `access_token` SHOULD be used to send push notifications.
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- If `allowed_key_list` are returned, the client SHOULD decrypt each token by generating an `AES-GCM` symmetric key from the Diffie–Hellman between the target client and itself.
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If AES decryption succeeds it will return a valid `uuid` which is what is used for access_token.
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The token SHOULD be used to send push notifications.
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- The response MUST be sent on the [partitioned topic](../../waku/standards/application/54/x3dh-sessions) of the sender and
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MUST NOT be encrypted using the [secure transport](../../waku/standards/application/53/x3dh) to facilitate the usage of ephemeral keys.
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- On receiving a response a client MUST verify `grant` to ensure that the server has been authorized to send push notification to a given client.
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### Sending Client
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Sending a push notification
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- When sending a push notification, only the `installation_id` for the devices targeted by the message SHOULD be used.
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- If a message is for all the user devices, all the `installation_id` known to the client MAY be used.
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- The number of devices MAY be capped in order to reduce resource consumption.
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- At least 3 devices SHOULD be targeted, ordered by last activity.
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- For any device that a token is available, or that
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a token is successfully queried,
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a push notification message SHOULD be sent to the corresponding push notification server.
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```protobuf
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message PushNotification {
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string access_token = 1;
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string chat_id = 2;
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bytes public_key = 3;
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string installation_id = 4;
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bytes message = 5;
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PushNotificationType type = 6;
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enum PushNotificationType {
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UNKNOWN_PUSH_NOTIFICATION_TYPE = 0;
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MESSAGE = 1;
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MENTION = 2;
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}
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bytes author = 7;
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}
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message PushNotificationRequest {
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repeated PushNotification requests = 1;
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bytes message_id = 2;
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}
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```
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#### Handle Notification Request:
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- A `PushNotificationRequest` message MUST be wrapped in a
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[`ApplicationMetadataMessage`](../62/payloads) with type set to `PUSH_NOTIFICATION_REQUEST`.
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- Where `message` is the encrypted payload of the message and `chat_id` is the `SHAKE-256` of the `chat_id`.
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`message_id` is the id of the message `author` is the `SHAKE-256` of the public key of the sender.
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- If multiple server are available for a given push notification, only one notification MUST be sent.
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- If no response is received a client SHOULD wait at least 3 seconds,
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after which the request MAY be retried against a different server.
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- This message SHOULD be sent using an ephemeral key.
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On receiving the message, the push notification server MUST validate the access token.
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If the access token is valid, a notification MUST be sent to the
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[gorush](https://github.com/appleboy/gorush) instance with the following data:
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```yaml
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{
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"notifications": [
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{
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"tokens": ["token_a", "token_b"],
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"platform": 1,
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"message": "You have a new message",
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"data": {
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"chat_id": chat_id,
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"message": message,
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"installation_ids": [installation_id_1, installation_id_2]
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}
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}
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]
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}
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```
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Where platform is 1 for iOS and 2 for Firebase, according to the [gorush documentation](https://github.com/appleboy/gorush).
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A server MUST return a response message:
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```protobuf
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message PushNotificationReport {
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bool success = 1;
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ErrorType error = 2;
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enum ErrorType {
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UNKNOWN_ERROR_TYPE = 0;
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WRONG_TOKEN = 1;
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INTERNAL_ERROR = 2;
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NOT_REGISTERED = 3;
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}
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bytes public_key = 3;
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string installation_id = 4;
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}
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```
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```protobuf
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message PushNotificationResponse {
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bytes message_id = 1;
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repeated PushNotificationReport reports = 2;
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}
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```
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Where `message_id` is the `message_id` sent by the client.
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#### Handle Notification Response:
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- A `PushNotificationResponse` message MUST be wrapped in a [`ApplicationMetadataMessage`](../62/payloads) with type set to `PUSH_NOTIFICATION_RESPONSE`.
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- The response MUST be sent on the [partitioned topic](../../waku/standards/application/54/x3dh-sessions) of the sender and
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MUST not be encrypted using the [secure transport](../../waku/standards/application/53/x3dh) to facilitate the usage of ephemeral keys.
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- If the request is accepted `success` MUST be set to `true`. Otherwise `success` MUST be set to `false`.
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- If `error` is `BAD_TOKEN` the client MAY query again the server for the token and retry the request.
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- If `error` is `INTERNAL_ERROR` the client MAY retry the request.
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### Protobuf Description
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#### PushNotificationRegistration:
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`token_type`: the type of token. Currently supported is `APN_TOKEN` for Apple Push.<br />
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`device_token`: the actual push notification token sent by `Firebase` or `APN` and `FIREBASE_TOKEN` for firebase.<br />
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`installation_id`: the `installation_id` of the device.<br />
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`access_token`: the access token that will be given to clients to send push notifications.<br />
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`enabled`: whether the device wants to be sent push notifications.<br />
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`version`: a monotonically increasing number identifying the current `PushNotificationRegistration`.
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Any time anything is changed in the record it MUST be increased by the client, otherwise the request will not be accepted.<br />
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`allowed_key_list`: a list of `access_token` encrypted with the AES key generated by Diffie–Hellman between the publisher and the
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allowed contact.<br />
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`blocked_chat_list`: a list of `SHA2-256` hashes of chat ids. Any chat id in this list will not trigger a notification.<br />
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`unregister`: whether the account should be unregistered.<br />
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`grant`: the grant for this specific server.<br />
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`allow_from_contacts_only`: whether the client only wants push notifications from contacts.<br />
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`apn_topic`: the APN topic for the push notification.<br />
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`block_mentions`: whether the client does not want to be notified on mentions.<br />
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`allowed_mentions_chat_list`: a list of SHA2-256 hashes of chat ids where we want to receive mentions.<br />
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DATA DISCLOSED
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- Type of device owned by a given user.
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- The `FIREBASE` or `APN` push notification token,
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- Hash of the `chat_id` a user is not interested in for notifications,
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- The number of times a push notification record has been modified by the user,
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- The number of contacts a client has, in case `allowed_key_list` is set.
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#### PushNotificationRegistrationResponse:
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`success`: whether the registration was successful<br />
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`error`: the error type, if any<br />
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`request_id`: the `SHAKE-256` hash of the `signature` of the request<br />
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`preferences`: the server stored preferences in case of an error<br />
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#### ContactCodeAdvertisement:
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`push_notification_info`: the information for each device advertised
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DATA DISCLOSED
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- The chat key of the sender
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#### PushNotificationQuery:
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`public_keys`: the `SHAKE-256` of the public keys the client is interested in
|
||
|
||
DATA DISCLOSED
|
||
- The hash of the public keys the client is interested in
|
||
|
||
#### PushNotificationQueryInfo:
|
||
`access_token`: the access token used to send a push notification<br />
|
||
`installation_id`: the `installation_id` of the device associated with the `access_token`<br />
|
||
`public_key`: the `SHAKE-256` of the public key associated with this `access_token` and `installation_id`.<br />
|
||
`allowed_key_list`: a list of encrypted access tokens to be returned to the client in case there’s any filtering on public keys in place.<br />
|
||
`grant`: the grant used to register with this server.<br />
|
||
`version`: the version of the registration on the server.<br />
|
||
`server_public_key`: the compressed public key of the server.<br />
|
||
|
||
#### PushNotificationQueryResponse:
|
||
`info`: a list of `PushNotificationQueryInfo`.<br />
|
||
`message_id`: the message id of the `PushNotificationQueryInfo` the server is replying to.<br />
|
||
`success`: whether the query was successful.<br />
|
||
|
||
#### PushNotification:
|
||
`access_token`: the access token used to send a push notification.<br />
|
||
`chat_id`: the `SHAKE-256` of the `chat_id`.<br />
|
||
`public_key`: the `SHAKE-256` of the compressed public key of the receiving client.<br />
|
||
`installation_id`: the `installation_id` of the receiving client.<br />
|
||
`message`: the encrypted message that is being notified on.<br />
|
||
`type`: the type of the push notification, either `MESSAGE` or `MENTION`<br />
|
||
`author`: the `SHAKE-256` of the public key of the sender
|
||
|
||
Data disclosed
|
||
- The `SHAKE-256` hash of the `chat_id` the notification is to be sent for
|
||
|
||
- The cypher text of the message
|
||
|
||
- The `SHAKE-256` hash of the public key of the sender
|
||
|
||
- The type of notification
|
||
|
||
#### PushNotificationRequest:
|
||
`requests`: a list of PushNotification<br />
|
||
`message_id`: the [Status message id](../62/payloads)
|
||
|
||
Data disclosed
|
||
- The status `message_id` for which the notification is for
|
||
|
||
#### PushNotificationResponse:
|
||
`message_id`: the `message_id` being notified on.<br />
|
||
`reports`: a list of `PushNotificationReport`
|
||
|
||
#### PushNotificationReport:
|
||
`success`: whether the push notification was successful.<br />
|
||
`error`: the type of the error in case of failure.<br />
|
||
`public_key`: the public key of the user being notified.<br />
|
||
`installation_id`: the `installation_id` of the user being notified.
|
||
|
||
### Anonymous Mode
|
||
In order to preserve privacy, the client MAY provide anonymous mode of operations to propagate information about the user.
|
||
A client in anonymous mode can register with the server using a key that is different from their chat key.
|
||
This will hide their real chat key. This public key is effectively a secret and
|
||
SHOULD only be disclosed to clients approved to notify a user.
|
||
|
||
- A client MAY advertise the access token on the [contact-code topic](../../waku/standards/application/53/x3dh) of the key generated.
|
||
|
||
- A client MAY share their public key contact updates in the [protobuf record](https://developers.google.com/protocol-buffers/).
|
||
|
||
- A client receiving a push notification public key SHOULD listen to the contact code topic of the push notification public key for updates.
|
||
|
||
The method described above effectively does not share the identity of the sender nor the receiver to the server, but
|
||
MAY result in missing push notifications as the propagation of the secret is left to the client.
|
||
This can be mitigated by [device syncing](../62/payloads), but not completely addressed.
|
||
|
||
## Security/Privacy Considerations
|
||
If anonymous mode is not used, when registering with a push notification service a client will disclose:
|
||
- The devices that will receive notifications.
|
||
|
||
- The chat key.
|
||
|
||
A client MAY disclose:
|
||
- The hash of the `chat_id` they want to filter out.
|
||
|
||
When running in anonymous mode, the client’s chat key is not disclosed.
|
||
|
||
When querying a push notification server a client will disclose:
|
||
- That it is interested in sending push notification to another client, but
|
||
querying client’s chat key is not disclosed.
|
||
|
||
When sending a push notification a client will disclose:
|
||
- The `shake-256` of the `chat_id`.
|
||
|
||
## Copyright
|
||
|
||
Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
|
||
|
||
## References
|
||
1. [PUSH-NOTIFICATION-SERVER, Initial Specification](https://github.com/status-im/specs/blob/master/docs/raw/push-notification-server)
|
||
2. [Push Notification, Apple Developer](https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/APNSOverview.html#//apple_ref/doc/uid/TP40008194-CH8-SW1)
|
||
3. [Firebase](https://firebase.google.com)
|
||
4. [13/WAKU2-STORE](../../waku/standards/core/13/store)
|
||
5. [gorush](https://github.com/appleboy/gorush)
|
||
6. [54/WAKU2-X3DH-SESSIONS](../../waku/standards/application/54/x3dh-sessions)
|
||
7. [62/PAYLOAD](../62/payloads)
|
||
8. [SHAKE-256](https://nvlpubs.nist.gov/nistpubs/fips/nist.fips.202.pdf)
|
||
9. [Protocol Buffers](https://developers.google.com/protocol-buffers)
|
||
10. [53/WAKU2-X3DH](../../waku/standards/application/53/x3dh)
|