- Status: draft
- Editor: Oskar Thorén firstname.lastname@example.org
- Contributors: Sanaz Taheri email@example.com , Hanno Cornelius firstname.lastname@example.org
Waku is a privacy-preserving peer-to-peer messaging protocol for resource restricted devices. It implements PubSub over libp2p and adds capabilities on top of it. These capabilities are: (i) retrieving historical messages for mostly-offline devices (ii) adaptive nodes, allowing for heterogeneous nodes to contribute, and (iii) bandwidth preservation for light nodes. This makes it ideal for running a p2p protocol on mobile and in similarly restricted environments.
Historically, it has its roots in Waku v1, which stems from Whisper, originally part of the Ethereum stack. However, Waku v2 acts more as a thin wrapper for PubSub and has a different API. It is implemented in an iterative manner where initial focus is on porting essential functionality to libp2p. See rough road map.
Motivation and goals #
Generalized messaging. Many applications require some form of messaging protocol to communicate between different subsystems or different nodes. This messaging can be human-to-human or machine-to-machine or a mix.
Peer-to-peer. These applications sometimes have requirements that make them suitable for peer-to-peer solutions.
Resource restricted. These applications often run in constrained environments, where resources or the environment is restricted in some fashion. E.g.:
- limited bandwidth, CPU, memory, disk, battery, etc
- not being publicly connectable
- only being intermittently connected; mostly-offline
- Privacy. These applications have a desire for some privacy guarantees, such as pseudonymity, metadata protection in transit, etc.
Waku provides a solution that satisfies these goals in a reasonable matter.
Network interaction domains #
While Waku is best though of as a single cohesive thing, there are three network interaction domains: (a) gossip domain (b) discovery domain (c) req/resp domain.
Protocols and identifiers #
The current protocol identifiers are:
These protocols and their semantics are elaborated on in their own specs.
In addition, Waku v2 MAY make use of libp2p ping protocol with protocol id
for liveness checks between peers, or to keep peer-to-peer connections alive.
For the actual content being passed around, see the 7/WAKU-DATA spec.
Use of libp2p and protobuf #
Unless otherwise specified, all protocols are implemented over libp2p and use Protobuf by default. Since messages are exchanged over a bi-directional binary stream, as a convention, libp2p protocols prefix binary message payloads with the length of the message in bytes. This length integer is encoded as a protobuf varint.
Gossip domain #
See 11/WAKU2-RELAY spec for more details.
Default pubsub topic #
The default PubSub topic being used for Waku is currently:
This indicates that it relates to Waku, is version 2, is the default topic, and that the encoding of data field is protobuf.
The default PubSub topic SHOULD be used for all protocols. This ensures a connected network, as well some degree of metadata protection. It MAY be different if or when:
- Different applications have different message volume
- Topic sharding is introduced
- Encoding is changed
- Version is changed
Discovery domain #
The discovery domain is not yet specified. As such, currently static nodes should be used. Please refer to specific implementations for details on publicly available nodes, as these may change over time.
Request/reply domain #
This consists of two main protocols. They are used in order to get Waku to run in resource restricted environments, such as low bandwidth or being mostly offline.
Historical message support #
See 13/WAKU2-STORE spec for more details.
Content filtering #
See 12/WAKU2-FILTER spec for more details.
See the sequence diagram below for an overview of how the different protocols interact.
We have six nodes, A-F. The protocols initially mounted are indicated as such. The PubSub topics
pubtopic2is used for routing and indicates that it is subscribed to messages on that topic for relay, see 11/WAKU2-RELAY for details. Ditto for 13/WAKU2-STORE where it indicates that these messages are persisted on that node.
Node A creates a WakuMessage
msg1with a ContentTopic
contentTopic1. See 14/WAKU2-MESSAGE for more details. If WakuMessage version is set to 1, we use the 6/WAKU1 compatible
datafield with encryption. See 7/WAKU-DATA for more details.
Node F requests to get messages filtered by PubSub topic
contentTopic1. Node D subscribes F to this filter and will in the future forward messages that match that filter. See 12/WAKU2-FILTER for more details.
Node A publishes
pubtopic1and subscribes to that relay topic pick it up. It then gets relayed further from B to D, but not C since it doesn’t subscribe to that topic. See 11/WAKU2-RELAY.
Node D saves
msg1for possible later retrieval by other nodes. See 13/WAKU2-STORE.
Node D also pushes
msg1to F, as it has previously subscribed F to this filter. See 12/WAKU2-FILTER.
At a later time, Node E comes online. It then requests messages matching
contentTopic1from Node D. Node D responds with messages meeting this (and possibly other) criteria. See 13/WAKU2-STORE.
Upgradability and Compatibility #
Compatibility with Waku v1 #
Waku v1 and Waku v2 are different protocols all together. They use a different transport protocol underneath; Waku v1 is devp2p RLPx based while Waku v2 uses libp2p. The protocols themselves also differ as does their data format. Compatibility can be achieved only by using a bridge that not only talks both devp2p RLPx and libp2p, but that also transfers (partially) the content of a packet from one version to the other.
See 15/WAKU-BRIDGE for details on a bidirectional bridge mode.
Each protocol layer of Waku v2 provides a distinct service and is associated with a separate set of security features and concerns. Therefore, the overall security of Waku v2 depends on how the different layers are utilized. In this section, we overview the security properties of Waku v2 protocols against a static adversarial model which is described below. Note that a more detailed security analysis of each Waku protocol is supplied in its respective specification as well.
Primary Adversarial Model #
In the primary adversarial model, we consider adversary as a passive entity that attempts to collect information from others to conduct an attack, but it does so without violating protocol definitions and instructions.
The following are not considered as part of the adversarial model:
- An adversary with a global view of all the peers and their connections.
- An adversary that can eavesdrop on communication links between arbitrary pairs of peers (unless the adversary is one end of the communication). Specifically, the communication channels are assumed to be secure.
Security Features #
Waku v2 by default guarantees pseudonymity for all of the protocol layers since parties do not have to disclose their true identity
and instead they utilize libp2p
PeerID as their identifiers.
While pseudonymity is an appealing security feature, it does not guarantee full anonymity since the actions taken under the same pseudonym
PeerID can be linked together and potentially result in the re-identification of the true actor.
Anonymity / Unlinkability #
At a high level, anonymity is the inability of an adversary in linking an actor to its data/performed action (the actor and action are context-dependent). To be precise about linkability, we use the term Personally Identifiable Information (PII) to refer to any piece of data that could potentially be used to uniquely identify a party. For example, the signature verification key, and the hash of one’s static IP address are unique for each user and hence count as PII. Notice that users' actions can be traced through their PIIs (e.g., signatures) and hence result in their re-identification risk. As such, we seek anonymity by avoiding linkability between actions and the actors / actors' PII. Concerning anonymity, Waku v2 provides the following features:
This feature signifies the unlinkability of a publisher to its published messages in the 11/WAKU2-RELAY protocol.
The Publisher-Message Unlinkability is enforced through the
StrictNoSign policy due to which the data fields of pubsub messages that count as PII for the publisher must be left unspecified.
Subscriber-Topic Unlinkability: This feature stands for the unlinkability of the subscriber to its subscribed topics in the 11/WAKU2-RELAY protocol. The Subscriber-Topic Unlinkability is achieved through the utilization of a single PubSub topic. As such, subscribers are not re-identifiable from their subscribed topic IDs as the entire network is linked to the same topic ID. This level of unlinkability / anonymity is known as k-anonymity where k is proportional to the system size (number of subscribers). Note that there is no hard limit on the number of the pubsub topics, however, the use of one topic is recommended for the sake of anonymity.
Spam protection #
This property indicates that no adversary can flood the system (i.e., publishing a large number of messages in a short amount of time), either accidentally or deliberately, with any kind of message i.e. even if the message content is valid or useful.
Spam protection is partly provided in
11/WAKU2-RELAY through the scoring mechanism provided for by GossipSub v1.1.
At a high level, peers utilize a scoring function to locally score the behavior of their connections and remove peers with a low score.
Data confidentiality, Integrity, and Authenticity #
Confidentiality can be addressed through data encryption whereas integrity and authenticity are achievable through digital signatures. These features are provided for in 14/WAKU2-MESSAGE (version 1)` through payload encryption as well as encrypted signatures.
Security Considerations #
Lack of anonymity/unlinkability in the protocols involving direct connections including
The anonymity/unlinkability is not guaranteed in the protocols like
12/WAKU2-FILTER where peers need to have direct connections to benefit from the designated service.
This is because during the direct connections peers utilize
PeerID to identify each other,
therefore the service obtained in the protocol is linkable to the beneficiary’s
PeerID (which counts as PII).
13/WAKU2-STORE, the queried node would be able to link the querying node’s
PeerID to its queried topics.
Likewise, in the
12/WAKU2-FILTER, a full node can link the light node’s
PeerIDs to its content filter.
Future work #
We are actively working on the following features to be added to Waku v2.
Economic Spam resistance:
We aim to enable an incentivized spam protection technique to enhance
11/WAKU2-RELAY by using rate limiting nullifiers.
More details on this can be found in 17/WAKU2-RLNRELAY.
In this advanced method, peers are limited to a certain rate of messaging per epoch and an immediate financial penalty is enforced for spammers who break this rate.
Prevention of Denial of Service (DoS) and Node Incentivization:
Denial of service signifies the case where an adversarial node exhausts another node’s service capacity (e.g., by making a large number of requests) and makes it unavailable to the rest of the system.
DoS attack is to be mitigated through the accounting model as described in 18/WAKU2-SWAP.
In a nutshell, peers have to pay for the service they obtain from each other.
In addition to incentivizing the service provider, accounting also makes DoS attacks costly for malicious peers.
The accounting model can be used in
12/WAKU2-FILTER to protect against DoS attacks.
Additionally, this gives node operators who provide a useful service to the network an incentive to perform that service. See 18/WAKU2-SWAP for more details on this piece of work.
Appendix A: Implementation Notes #
Implementation Matrix #
There are multiple implementations of Waku v2 and its protocols:
Below you can find an overview of the specs that they implement as they relate to Waku. This includes Waku v1 specs, as they are used for bridging between the two networks.
|Spec||nim-waku (Nim)||go-waku (Go)||js-waku (Node JS)||js-waku (Browser JS)|
Recommendations for clients #
To implement a minimal Waku v2 client, we recommend implementing the following subset in the following order:
- 10/WAKU2 - this spec
- 11/WAKU2-RELAY - for basic operation
- 14/WAKU2-MESSAGE - version 0 (unencrypted)
- 13/WAKU2-STORE - for historical messaging (query mode only)
To get compatibility with Waku v1:
For an interoperable keep-alive mechanism:
- libp2p ping protocol, with periodic pings to connected peers
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