13/WAKU2-STORE

13/WAKU2-STORE

Waku v2 Store

This specification explains the Waku 13/WAKU2-STORE protocol which enables querying of messages received through relay protocol and stored by other nodes. It also supports pagination for more efficient querying of historical messages.

Protocol identifier*: /vac/waku/store/2.0.0-beta2

Design Requirements #

Nodes willing to provide storage service using 13/WAKU2-STORE protocol SHOULD provide a complete and full view of message history. As such, they are required to be highly available and in specific have a high uptime to consistently receive and store network messages. The high uptime requirement makes sure that no message is missed out hence a complete and intact view of the message history is delivered to the querying nodes. Nevertheless, in case that storage provider nodes cannot afford high availability, the querying nodes may retrieve the historical messages from multiple sources to achieve a full and intact view of the past.

Security Consideration #

The main security consideration to take into account while using 13/WAKU2-STORE is that a querying node have to reveal their content filters of interest to the queried node, hence potentially compromising their privacy.

Terminology #

The term Personally identifiable information (PII) refers to any piece of data that can be used to uniquely identify a user. 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.

Adversarial Model #

Any peer running the 13/WAKU2-STORE protocol, i.e. both the querying node and the queried node, are considered as an adversary. Furthermore, we currently consider the adversary as a passive entity that attempts to collect information from other peers to conduct an attack but it does so without violating protocol definitions and instructions. As we evolve the protocol, further adversarial models will be considered. For example, under the passive adversarial model, no malicious node hides or lies about the history of messages as it is against the description of the 13/WAKU2-STORE protocol.

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.

Wire Specification #

Peers communicate with each other using a request / response API. The messages sent are Protobuf RPC messages which are implemented using protocol buffers v3. The followings are the specifications of the Protobuf messages.

Payloads #

syntax = "proto3";

message Index {
  bytes digest = 1;
  double receivedTime = 2;
}

message PagingInfo {
  uint64 pageSize = 1;
  Index cursor = 2;
  enum Direction {
    BACKWARD = 0;
    FORWARD = 1;
  }
  Direction direction = 3;
}

message ContentFilter {
  string contentTopic = 1;
}

message HistoryQuery {
  // the first field is reserved for future use
  string pubsubtopic = 2;
  repeated ContentFilter contentFilters = 3;
  PagingInfo pagingInfo = 4;
}

message HistoryResponse {
  // the first field is reserved for future use
  repeated WakuMessage messages = 2;
  PagingInfo pagingInfo = 3;
}

message HistoryRPC {
  string request_id = 1;
  HistoryQuery query = 2;
  HistoryResponse response = 3;
}

Index #

To perform pagination, each WakuMessage stored at a node running the 13/WAKU2-STORE protocol is associated with a unique Index that encapsulates the following parts.

  • digest: a sequence of bytes representing the SHA256 hash of a WakuMessage. The hash is computed over the concatenation of contentTopic and payload fields of a WakuMessage (see 14/WAKU2-MESSAGE).
  • receivedTime: the UNIX time at which the waku message is received by the node running the 13/WAKU2-STORE protocol.

PagingInfo #

PagingInfo holds the information required for pagination. It consists of the following components.

  • pageSize: A positive integer indicating the number of queried WakuMessages in a HistoryQuery (or retrieved WakuMessages in a HistoryResponse).
  • cursor: holds the Index of a WakuMessage.
  • direction: indicates the direction of paging which can be either FORWARD or BACKWARD.

ContentFilter #

ContentFilter carries the information required for filtering historical messages.

  • contentTopic represents the content topic of the queried historical Waku messages. This field maps to the contentTopic field of the 14/WAKU2-MESSAGE.

HistoryQuery #

RPC call to query historical messages.

  • The pubsubTopic field MUST indicate the pubsub topic of the historical messages to be retrieved. This field denotes the pubsub topic on which waku messages are published. This field maps to topicIDs field of Message in 11/WAKU2-RELAY. Leaving this field empty means no filter on the pubsub topic of message history is requested. This field SHOULD be left empty in order to retrieve the historical waku messages regardless of the pubsub topics on which they are published.
  • The contentFilters field MUST indicate the list of content filters based on which the historical messages are to be retrieved. Leaving this field empty means no filter on the content topic of message history is required. This field SHOULD be left empty in order to retrieve historical waku messages regardless of their content topics.
  • PagingInfo holds the information required for pagination. Its pageSize field indicates the number of WakuMessages to be included in the corresponding HistoryResponse. If the pageSize is zero then no pagination is required. If the pageSize exceeds a threshold then the threshold value shall be used instead. In the forward pagination request, the messages field of the HistoryResponse shall contain at maximum the pageSize amount of waku messages whose Index values are larger than the given cursor (and vise versa for the backward pagination). Note that the cursor of a HistoryQuery may be empty (e.g., for the initial query), as such, and depending on whether the direction is BACKWARD or FORWARD the last or the first pageSize waku messages shall be returned, respectively. The queried node MUST sort the WakuMessages based on their Index, where the receivedTime constitutes the most significant part and the digest comes next, and then perform pagination on the sorted result. As such, the retrieved page contains an ordered list of WakuMessages from the oldest message to the most recent one.

HistoryResponse #

RPC call to respond to a HistoryQuery call.

  • The messages field MUST contain the messages found, these are [WakuMessage] types as defined in the corresponding specification.
  • PagingInfo holds the paging information based on which the querying node can resume its further history queries. The pageSize indicates the number of returned waku messages (i.e., the number of messages included in the messages field of HistoryResponse). The direction is the same direction as in the corresponding HistoryQuery. In the forward pagination, the cursor holds the Index of the last message in the HistoryResponse messages (and the first message in the backward paging). The requester shall embed the returned cursor inside its next HistoryQuery to retrieve the next page of the waku messages.
    The cursor obtained from one node SHOULD NOT be used in a request to another node because the result MAY be different.

Future Work #

  • Anonymous query: This feature guarantees that nodes can anonymously query historical messages from other nodes i.e., without disclosing the exact topics of waku messages they are interested in.
    As such, no adversary in the 13/WAKU2-STORE protocol would be able to learn which peer is interested in which content filters i.e., content topics of waku message. The current version of the 13/WAKU2-STORE protocol does not provide anonymity for historical queries as the querying node needs to directly connect to another node in the 13/WAKU2-STORE protocol and explicitly disclose the content filters of its interest to retrieve the corresponding messages. However, one can consider preserving anonymity through one of the following ways:
    • By hiding the source of the request i.e., anonymous communication. That is the querying node shall hide all its PII in its history request e.g., its IP address. This can happen by the utilization of a proxy server or by using Tor. Note that the current structure of historical requests does not embody any piece of PII, otherwise, such data fields must be treated carefully to achieve query anonymity.
    • By deploying secure 2-party computations in which the querying node obtains the historical messages of a certain topic whereas the queried node learns nothing about the query. Examples of such 2PC protocols are secure one-way Private Set Intersections (PSI).

Copyright #

Copyright and related rights waived via CC0.