docs.waku.org/docs/overview/concepts/content-topics.md

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Content Topics

Content Topics are metadata strings set by developers on outgoing messages to facilitate protocol-level features like selectively processing incoming messages (Relay or Filter) and retrieving historical messages (Store) that meet specific filtering criteria. Please refer to the WAKU2-TOPICS specification to learn more.

Content Topic Format

Here is the recommended format for content topics:

/{application-name}/{version}/{content-topic-name}/{encoding}

• application-name: This is the unique name of your decentralized application (dApp) to prevent conflicts with other dApps.
• version: Typically starting at 1, this field helps track breaking changes in your messages.
• content-topic-name: The specific name of the content topic used for filtering.
• encoding: The message serialization/encoding format, with Protocol Buffers (proto) being the recommended choice.

For instance, if your dApp is called SuperCrypto and it allows users to receive notifications and send private messages, you can consider using the following content topics:

• /supercrypto/1/notification/proto
• /supercrypto/1/private-message/proto

:::info While you can choose any encoding format for your Content Topic, we highly recommend using Protocol Buffers (proto) because of its efficiency. Choosing a lightweight format ensures optimal performance of your dApp. :::

Naming Considerations

When choosing a content topic, it is crucial to consider privacy implications. The Filter, Store, and Light Push protocols disclose content topics to peers, enabling said peer to link ip and content topic interests. Relay provides recipient anonymity thanks to GossipSub, but this may be lost if the content topic reveals information about the user.

:::info Waku is developing privacy-preserving features like Anonymous Filter Subscription for the Filter protocol and Anonymous Query for the Store protocol to hide content topics from potential adversaries. :::

You can preserve the anonymity of individual identities by increasing k-anonymity, where k is proportional to the network size (number of subscribers). This involves using a single content topic across the entire application or specific features such as notifications or private messages, allowing multiple users to share it.

However, maintaining functionality with a single content topic can introduce complexity. We recommend switching functionality using the Protocol Buffer message format. By doing so, applications can retain a high granularity and functionality while using a single content topic, preserving user privacy.