Waku Source

AuthorsOskar Thorén, Sanaz Taheri
StatusDraft
Version2.0.0-beta1

Table of Contents

Abstract

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.

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

  1. Generalized messaging. Many applications requires 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.

  2. Peer-to-peer. These applications sometimes have requirements that make them suitable for peer-to-peer solutions.

  3. 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
  1. 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:

  1. /vac/waku/relay/2.0.0-beta2
  2. /vac/waku/store/2.0.0-beta1
  3. /vac/waku/filter/2.0.0-beta1

These protocols and their semantics are elaborated on in their own specs.

For the actual content being passed around, see the Waku Message spec.

The WakuMessage spec being used is: 2.0.0-beta1.

Gossip domain

Protocol identifier*: /vac/waku/relay/2.0.0-beta1

See WakuRelay spec for more details.

Default pubsub topic

The default PubSub topic being used for Waku is currently: /waku/2/default-waku/proto

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

Discovery domain is not yet implemented. Currently static nodes should be used.

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

Protocol identifier*: /vac/waku/store/2.0.0-beta1

See WakuStore spec for more details.

Content filtering

Protocol identifier*: /vac/waku/filter/2.0.0-beta1

See WakuFilter spec for more details.

Upgradability and Compatibility

Compatibility with Waku v1

Waku v2 and Waku v1 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 bridge spec for details on a bridge mode.

Security

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). In specific, the communication channels are assumed to be secure.

Security Features

Pseudonymity

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 i.e., 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:

Publisher-Message Unlinkability: This feature signifies the unlinkability of a publisher to its published messages in the WakuRelay 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 WakuRelay 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 WakuRelay through scoring mechanism of 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, Authenticity

Confidentiality can be addressed through data encryption whereas integrity and authenticity are achievable through digital signatures. These features are enabled in WakuMessage v1 through payload encryption as well as encrypted signatures (see WakuMessage specs for further details).

Security Considerations

Lack of anonymity/unlinkability in the protocols involving direct connections including WakuStore and WakuFilter protocols: The anonymity/unlinkability is not guaranteed in the protocols like WakuStore and WakuFilter 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). In terms of WakuStore, the queried node would be able to link the querying node’s PeerID to its queried topics. Likewise, in the WakuFilter, 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 at the WakuRelay by using rate limiting nullifiers. More details on this can be found in Waku RLN Relay. 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): 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 Waku Swap Accounting specs. 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 WakuStore and WakuFilter to protect against DoS attacks.

Changelog

Next version

  • Add recommended default PubSub topic
  • Update relay and message spec version
  • Security analysis under the primary adversarial model is done

2.0.0-beta1

Initial draft version. Released 2020-09-17

Copyright

Copyright and related rights waived via CC0.

References

  1. Protocol Identifiers

  2. PubSub interface for libp2p (r2, 2019-02-01)

  3. GossipSub v1.0

  4. GossipSub v1.1

  5. Waku v1 spec

  6. Whisper spec (EIP627)

  7. Waku v2 plan

  8. Message Filtering (Wikipedia)

  9. Libp2p PubSub spec - topic validation