Waku is a family of decentralised communication protocols. The Waku Network (TWN) consists of independent nodes running Waku protocols. TWN needs incentivisation (shortened to i13n) to ensure proper node behaviour.
The goal of this document is to outline and contextualize our approach to TWN i13n. After providing an overview of Waku and relevant prior work, we focus on Waku Store - a client-server protocol for querying historical messages. We introduce a minimal viable addition to Store to enable i13n, and list research directions for future work.
Reputation only works if high reputation brings tangible benefits. For example, if nodes chose neighbors based on reputation, low-reputation nodes miss out on potential revenue. Reputation scores may be local (a node assigns scores to its neighbors) or global (each node gets a uniform score). Global reputation in its simplest form involves a trusted third party, although decentralised approaches are also possible.
Early P2P file-sharing networks employ reputation-based approaches and sticky defaults. For instance, the BitTorrent protocol rewards uploading peers with faster downloads. The download bandwidth available to a peer depends on how much it has uploaded. Moreover, peers share pieces of a file before having received it in whole. This non-monetary i13n policy has been proved to work in practice.
Bitcoin has introduced proof-of-work (PoW) for native monetary rewards in a P2P network. PoW miners are automatically assigned newly mined coins for generating blocks. Miners must expend physical resources to generate a block. If the block is invalid, these expenses are not compensated (implicit monetary punishment). Proof-of-stake (PoS), used in Ethereum and many other cryptocurrencies, introduces explicit monetary punishments. PoS validators lock up (stake) native tokens and get rewarded for validating blocks or slashed for misbehaviour.
Post-Bitcoin decentralised storage networks include Codex, Storj, Sia, Filecoin, IPFS. Their i13n methods combine techniques from early P2P file-sharing with blockchain-inspired reward mechanisms.
Waku is a [family of protocols](https://waku.org/about/architect) for a modular privacy-preserving censorship-resistant decentralised communication network. The backbone of Waku is the Relay protocol (and its spam-protected version [RLN-Relay](https://rfc.vac.dev/spec/17/)). Additionally, there are light protocols: Store, Filter, and Lightpush. Light protocols are also referred to as client-server protocols and request-response protocols.
A server is a node running Relay and a server-side of at least one light protocol. A client is a node running a client-side of any of the light protocols. A server may sometimes be referred to as a full node, and a client as a light node. There is no strict definition of a full node vs a light node in Waku (see [discussion](https://github.com/waku-org/research/issues/28)).
Waku has no consensus and no native token, which brings it closer to reputation-incentivised file-sharing networks. As of late 2023, Waku only operates under reputation-based rewards and punishments. While [RLN-Relay](https://rfc.vac.dev/spec/17/) adds monetary punishments for spammers, slashing is yet to be activated.
Monetary rewards and punishments should ideally be atomically linked with the node's behaviour. A benefit of blockchains in this respect is that the desired behaviour of miners or validators can be verified automatically. Enforcing atomicity in a communication network is more challenging: it is non-trivial to prove that a given piece of data has been relayed.
Our goal is to combine monetary and reputation-based incentives for Waku. Monetary incentives have demonstrated their robustness in blockchains. We think they are necessary to scale the network beyond the initial phase when it's maintained altruistically.
We define a _relevant_ message as a message that matches client-defined criteria (e.g., relayed within a given time frame). Upon receiving a request, a server should quickly send back a response containing all and only relevant messages.
In this document, we focus on the simplest proof-of-concept (PoC) i13n for Store. Compared to the fully-fledged protocol, the PoC version is simplified in the following ways:
For PoC, we assume a constant price per hour of history. This price and the blockchain address of the server are assumed to be common knowledge. This simplifies the client-server interaction, avoiding the price negotiation step.
In the future versions of the protocol, the price will be negotiated and will depend on multiple parameters, such as the total size of the relevant messages in the response.
For the PoC, each request is paid for with a separate transaction. The transaction hash (`txid`) acts as a proof of payment. The server verifies the payment by ensuring that:
In light of these criteria, we suggest that the client pays first. This is simpler than splitting the payment, or involving an extra atomicity-enforcing mechanism. Moreover, pre-payment is arguably more privacy-preserving than post-payment, which encourages servers to deanonymise clients to prevent fraud.
- The ban mechanism can theoretically be abused. For instance, a competitor may attack the victim server and cause the clients who were awaiting the response to ban that server. Countermeasure: prevent DoS-attacks.
As there is no consensus over past messages, a client may want to query multiple servers and merge their responses. Cross-checking helps ensure that servers are a) not censoring real messages; b) not injecting fake messages into history. Cross-checking is absent in PoC but may be considered later.
We should think about what the success metrics for an incentivised protocol are, and how to measure them both in simulated settings, as well as in a live network.
- Analyze decentralised storage protocols and their relevance e.g. as back-end storage for Store servers - see https://github.com/waku-org/research/issues/34
- Analyze the role of message senders, in particular, whether they should pay for sending non-ephemeral messages - see https://github.com/waku-org/research/issues/32
