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14/WAKU2-MESSAGE

Waku v2 Message

draft

Oskar Thorén <oskar@status.im>

Sanaz Taheri <sanaz@status.im>

This specification provides a way to encapsulate messages sent over Waku with specific information security goals.

Motivation

When sending messages over Waku there are multiple concerns:

We may have a separate encryption layer as part of our application
We may want to provide efficient routing for resource restricted devices
We may want to provide compatibility with Waku v1 envelopes
We may want payloads to be encrypted by default
We may want to provide unlinkability for metadata protection

This specification attempts to provide for these various requirements.

WakuMessage

A WakuMessage is what is being passed around by the other protocols, such as WakuRelay, WakuStore, and WakuFilter.

The payload field SHOULD contain whatever payload is being sent. See section below on payload encryption.

The contentTopic field SHOULD be filled out to allow for content-based filtering. See 12/WAKU2-FILTER and 13/WAKU2-STORE for more details. To enable a bidirectional bridge with Waku v1 see 15/WAKU2-BRIDGE for further requirements on this field.

The version field MAY be filled out to allow for various types of payload encryption. Omitting it means the version is 0.

The timestamp field MAY be filled out to signify the time at which the message is generated by its sender. This field holds the Unix epoch time in nanoseconds. Omitting it means the timestamp is unspecified.

Payloads

Payloads are implemented using protocol buffers v3.

syntax = "proto3";

message WakuMessage {
  bytes payload = 1;
  string contentTopic = 2;
  uint32 version = 3;
  sint64 timestamp = 10;
}

Payload encryption

Payload encryption depends on the version field.

Version 0

This indicates that the payload SHOULD be either unencrypted or that encryption is done at a separate layer outside of Waku.

Version 1

This indicates that payloads MUST be encrypted using WAKU2-PAYLOAD.

This provides for asymmetric and symmetric encryption. Key agreement is out of band. It also provides an encrypted signature and padding for some form of unlinkability.

Version 2

This indicates that payloads MUST be encoded using 35/WAKU-NOISE.

This provides for symmetric encryption and asymmetric key-exchange protocols.

Differences from Whisper / Waku v1 envelopes

In Whisper and Waku v1, an envelope contains the following fields: expiry, ttl, topic, data, nonce.

Since Waku v2 is using libp2p PubSub, some of these fields can be dropped. The previous topic field corresponds to contentTopic. The previous data field corresponds to the payload field.

Security Consideration

Confidentiality, integrity, and authenticity

It is up to the application layer as to what level confidentiality, integrity and authenticity of the payload of WakuMessage matters. Accordingly, the application layer shall utilize the encryption and signature schemes supported in WAKU2 to meet the application-specific privacy needs. The set of supported schemes in WAKU2 is presented in WAKU2-PAYLOAD.

Reliability of the WakuMessage timestamp

The timestamp field in WakuMessage is set by the sender. Because timestamp isn't independently verified, this field is prone to exploit and misuse. It should not solely be relied upon for operations such as message ordering.

For example, a malicious node 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 the WakuMessage's timestamp field 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 6/PAYLOADS.

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