# 14/WAKU2-MESSAGE | Vac Research
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# 14/WAKU2-MESSAGE

- Status: stable
- Category: Standards Track
- Editor: Hanno Cornelius <hanno@status.im>
- Contributors:
  - Sanaz Taheri <sanaz@status.im>
  - Aaryamann Challani <p1ge0nh8er@proton.me>
  - Lorenzo Delgado <lorenzo@status.im>
  - Abhimanyu Rawat <abhi@status.im>
  - Oskar Thorén <oskarth@titanproxy.com>

## Abstract​

10/WAKU2 is a family of modular peer-to-peer protocols for secure communication. These protocols are designed to be secure, privacy-preserving, and censorship-resistant and can run in resource-restricted environments. At a high level, 10/WAKU2 implements a publish/subscribe messaging pattern over libp2p and adds capabilities.

The present document specifies the 10/WAKU2 message format. A way to encapsulate the messages sent with specific information security goals, and Whisper/6/WAKU1 backward compatibility.

## Motivation​

When sending messages over Waku, there are multiple requirements:

- One may have a separate encryption layer as part of the application.
- One may want to provide efficient routing for resource-restricted devices.
- One may want to provide compatibility with 6/WAKU1 envelopes.
- One may want encrypted payloads by default.
- One may want to provide unlinkability to get metadata protection.

This specification attempts to provide for these various requirements.

## Semantics​

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.

### Waku Message​

A `WakuMessage` is constituted by the combination of data payload and attributes that, for example, a publisher sends to a topic and is eventually delivered to subscribers.

The `WakuMessage` attributes are key-value pairs of metadata associated with a message. The message data payload is the part of the transmitted `WakuMessage` that is the actual message information. The data payload is also treated as a `WakuMessage` attribute for convenience.

### Message Attributes​

- The `payload` attribute MUST contain the message data payload to be sent.

- The `content_topic` attribute MUST specify a string identifier that can be used for content-based filtering, as described in 23/WAKU2-TOPICS.

- The `meta` attribute, if present, contains an arbitrary application-specific variable-length byte array with a maximum length limit of 64 bytes. This attribute can be utilized to convey supplementary details to various 10/WAKU2 protocols, thereby enabling customized processing based on its contents.

- The `version` attribute, if present, contains a version number to discriminate different types of payload encryption. If omitted, the value SHOULD be interpreted as version 0.

- The `timestamp` attribute, if present, signifies the time at which the message was generated by its sender. This attribute MAY contain the Unix epoch time in nanoseconds. If the attribute is omitted, it SHOULD be interpreted as timestamp 0.

- The `rate_limit_proof` attribute, if present, contains a rate limit proof encoded as per 17/WAKU2-RLN-RELAY.

- The `ephemeral` attribute, if present, signifies the transient nature of the message. For example, an ephemeral message SHOULD not be persisted by other nodes on the same network. If this attribute is set to `true`, the message SHOULD be interpreted as ephemeral. If, instead, the attribute is omitted or set to `false`, the message SHOULD be interpreted as non-ephemeral.

## Wire Format​

The `WakuMessage` wire format is specified using protocol buffers v3.

    syntax = "proto3";

    message WakuMessage {
      bytes payload = 1;
      string content_topic = 2;
      optional uint32 version = 3;
      optional sint64 timestamp = 10;
      optional bytes meta = 11;
      optional bytes rate_limit_proof = 21;
      optional bool ephemeral = 31;
    }

An example proto file following this specification can be found here (vacp2p/waku).

## Payload encryption​

The `WakuMessage` payload MAY be encrypted. The message `version` attribute indicates the schema used to encrypt the payload data.

- Version 0: The payload SHOULD be interpreted as unencrypted; additionally, it CAN indicate that the message payload has been encrypted at the application layer.

- Version 1: The payload SHOULD be encrypted using 6/WAKU1 payload encryption specified in 26/WAKU-PAYLOAD. This provides asymmetric and symmetric encryption. The key agreement is performed out of band. And provides an encrypted signature and padding for some form of unlinkability.

- Version 2: The payload SHOULD be encoded according to WAKU2-NOISE. The Waku Noise protocol provides symmetric encryption and asymmetric key exchange.

Any `version` value not included in this list is reserved for future specification. And, in this case, the payload SHOULD be interpreted as unencrypted by the Waku layer.

## Whisper/6/WAKU1 envelope compatibility​

Whisper/6/WAKU1 envelopes are compatible with Waku messages format.

- Whisper/6/WAKU1 `topic` field SHOULD be mapped to Waku message's `content_topic` attribute.
- Whisper/6/WAKU1 `data` field SHOULD be mapped to Waku message's `payload` attribute.

10/WAKU2 implements a publish/subscribe messaging pattern over libp2p. This makes some Whisper/6/WAKU1 envelope fields redundant (e.g., `expiry`, `ttl`, `topic`, etc.), so they can be ignored.

## Deterministic message hashing​

In Protocol Buffers v3, the deterministic serialization is not canonical across the different implementations and languages. It is also unstable across different builds with schema changes due to unknown fields.

To overcome this interoperability limitation, a 10/WAKU2 message's hash MUST be computed following this schema:

    message_hash = sha256(concat(pubsub_topic, message.payload, message.content_topic, message.meta, message.timestamp))

If an optional attribute, such as `meta`, is absent, the concatenation of attributes SHOULD exclude it. This recommendation is made to ensure that the concatenation process proceeds smoothly when certain attributes are missing and to maintain backward compatibility.

This hashing schema is deemed appropriate for use cases where a cross-implementation deterministic hash is needed, such as message deduplication and integrity validation. The collision probability offered by this hashing schema can be considered negligible. This is due to the deterministic concatenation order of the message attributes, coupled with using a SHA-2 (256-bit) hashing algorithm.

### Test vectors​

The `WakuMessage` hash computation (`meta` size of 12 bytes):

    pubsub_topic = "/waku/2/default-waku/proto" (0x2f77616b752f322f64656661756c742d77616b752f70726f746f)
    message.payload = 0x010203045445535405060708
    message.content_topic = "/waku/2/default-content/proto" (0x2f77616b752f322f64656661756c742d636f6e74656e742f70726f746f)
    message.meta = 0x73757065722d736563726574
    message.timestamp = 0x175789bfa23f8400

    message_hash = 0x64cce733fed134e83da02b02c6f689814872b1a0ac97ea56b76095c3c72bfe05

The `WakuMessage` hash computation (`meta` size of 64 bytes):

    pubsub_topic = "/waku/2/default-waku/proto" (0x2f77616b752f322f64656661756c742d77616b752f70726f746f)
    message.payload = 0x010203045445535405060708
    message.content_topic = "/waku/2/default-content/proto" (0x2f77616b752f322f64656661756c742d636f6e74656e742f70726f746f)
    message.meta = 0x000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f
    message.timestamp = 0x175789bfa23f8400

    message_hash = 0x7158b6498753313368b9af8f6e0a0a05104f68f972981da42a43bc53fb0c1b27

The `WakuMessage` hash computation (`meta` attribute not present):

    pubsub_topic = "/waku/2/default-waku/proto" (0x2f77616b752f322f64656661756c742d77616b752f70726f746f)
    message.payload = 0x010203045445535405060708
    message.content_topic = "/waku/2/default-content/proto" (0x2f77616b752f322f64656661756c742d636f6e74656e742f70726f746f)
    message.meta = <not-present>
    message.timestamp = 0x175789bfa23f8400

    message_hash = 0xa2554498b31f5bcdfcbf7fa58ad1c2d45f0254f3f8110a85588ec3cf10720fd8

The `WakuMessage` hash computation (`payload` length 0):

    pubsub_topic = "/waku/2/default-waku/proto" (0x2f77616b752f322f64656661756c742d77616b752f70726f746f)
    message.payload = []
    message.content_topic = "/waku/2/default-content/proto" (0x2f77616b752f322f64656661756c742d636f6e74656e742f70726f746f)
    message.meta = 0x73757065722d736563726574
    message.timestamp = 0x175789bfa23f8400

    message_hash = 0x483ea950cb63f9b9d6926b262bb36194d3f40a0463ce8446228350bd44e96de4

## Security Considerations​

### Confidentiality, integrity, and authenticity​

The level of confidentiality, integrity, and authenticity of the `WakuMessage` payload is discretionary. Accordingly, the application layer shall utilize the encryption and signature schemes supported by 10/WAKU2, to meet the application-specific privacy needs.

### Reliability of the `timestamp` attribute​

The message `timestamp` attribute is set by the sender. Therefore, because message timestamps aren’t independently verified, this attribute is prone to exploitation and misuse. It should not solely be relied upon for operations such as message ordering. For example, a malicious actor can arbitrarily set the `timestamp` of a `WakuMessage` to a high value so that it always shows up as the most recent message in a chat application. Applications using 10/WAKU2 messages’ `timestamp` attribute are RECOMMENDED to use additional methods for more robust message ordering. An example of how to deal with message ordering against adversarial message timestamps can be found in the Status protocol, see 62/STATUS-PAYLOADS.

### Reliability of the `ephemeral` attribute​

The message `ephemeral` attribute is set by the sender. Since there is currently no incentive mechanism for network participants to behave correctly, this attribute is inherently insecure. A malicious actor can tamper with the value of a Waku message’s `ephemeral` attribute, and the receiver would not be able to verify the integrity of the message.

## Copyright​

Copyright and related rights waived via CC0.

## References​

- 10/WAKU2
- 6/WAKU1
- 23/WAKU2-TOPICS
- 17/WAKU2-RLN-RELAY
- 64/WAKU2-NETWORK
- protocol buffers v3
- 26/WAKU-PAYLOAD
- WAKU2-NOISE
- 62/STATUS-PAYLOADS