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137 lines
6.2 KiB
Markdown
137 lines
6.2 KiB
Markdown
# WAKU-MAILSERVER
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<div class="rfc-meta">
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<table>
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<tr><th>Name</th><td>Waku Mailserver</td></tr>
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<tr><th>Status</th><td>deprecated</td></tr>
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<tr><th>Editor</th><td>Filip Dimitrijevic <filip@status.im></td></tr>
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<tr><th>Contributors</th><td>Adam Babik <adam@status.im><br>Oskar Thorén <oskar@status.im><br>Samuel Hawksby-Robinson <samuel@status.im></td></tr>
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</table>
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</div>
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## Abstract
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Being mostly offline is an intrinsic property of mobile clients.
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They need to save network transfer and battery consumption to avoid spending too much money or constant charging.
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Waku protocol, on the other hand, is an online protocol.
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Messages are available in the Waku network only for short period of time calculate in seconds.
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Waku Mailserver is a specification that allows messages to be stored permanently
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and allows the stored messages to be delivered to requesting client nodes,
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regardless if the messages are not available in the network due to the message TTL expiring.
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## `Mailserver`
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From the network perspective, a `Mailserver` is just like any other Waku node.
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The only difference is that a `Mailserver` has the capability of archiving messages
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and delivering them to its peers on-demand.
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It is important to notice that a `Mailserver` will only handle requests from its direct peers
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and exchanged packets between a `Mailserver` and a peer are p2p messages.
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### Archiving messages
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A node which wants to provide `Mailserver` functionality MUST store envelopes from
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incoming message packets (Waku packet-code `0x01`). The envelopes can be stored in any
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format, however they MUST be serialized and deserialized to the Waku envelope format.
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A `Mailserver` SHOULD store envelopes for all topics to be generally useful for any peer,
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however for specific use cases it MAY store envelopes for a subset of topics.
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### Requesting messages
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In order to request historic messages, a node MUST send a packet P2P Request (`0x7e`) to a peer providing `Mailserver` functionality.
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This packet requires one argument which MUST be a Waku envelope.
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In the Waku envelope's payload section, there MUST be RLP-encoded information about the details of the request:
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```golang
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[ Lower, Upper, Bloom, Limit, Cursor ]
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```
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`Lower`: 4-byte wide unsigned integer (UNIX time in seconds; oldest requested envelope's creation time)
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`Upper`: 4-byte wide unsigned integer (UNIX time in seconds; newest requested envelope's creation time)
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`Bloom`: 64-byte wide array of Waku topics encoded in a bloom filter to filter envelopes
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`Limit`: 4-byte wide unsigned integer limiting the number of returned envelopes
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`Cursor`: an array of a cursor returned from the previous request (optional)
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The `Cursor` field SHOULD be filled in if a number of envelopes between `Lower` and `Upper` is greater than `Limit`
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so that the requester can send another request using the obtained `Cursor` value.
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What exactly is in the `Cursor` is up to the implementation.
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The requester SHOULD NOT use a `Cursor` obtained from one `Mailserver` in a request to another `Mailserver` because the format or the result MAY be different.
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The envelope MUST be encrypted with a symmetric key agreed between the requester and the `Mailserver`.
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### Receiving historic messages
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Historic messages MUST be sent to a peer as a packet with a P2P Message code (`0x7f`) followed by an array of Waku envelopes.
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In order to receive historic messages from a `Mailserver`, a node MUST trust the selected `Mailserver`,
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that is allowed to send packets with the P2P Message code. By default, the node discards such packets.
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Received envelopes MUST be passed through the Waku envelope pipelines
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so that they are picked up by registered filters and passed to subscribers.
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For a requester, to know that all messages have been sent by a `Mailserver`,
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it SHOULD handle P2P Request Complete code (`0x7d`). This code is followed by the following parameters:
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```golang
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[ RequestID, LastEnvelopeHash, Cursor ]
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```
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* `RequestID`: 32-byte wide array with a Keccak-256 hash of the envelope containing the original request
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* `LastEnvelopeHash`: 32-byte wide array with a Keccak-256 hash of the last sent envelope for the request
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* `Cursor`: an array of a cursor returned from the previous request (optional)
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If `Cursor` is not empty, it means that not all messages were sent due to the set `Limit` in the request.
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One or more consecutive requests MAY be sent with `Cursor` field filled in order to receive the rest of the messages.
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## Security considerations
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### Confidentiality
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The node encrypts all Waku envelopes. A `Mailserver` node can not inspect their contents.
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### Altruistic and centralized operator risk
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In order to be useful, a `Mailserver` SHOULD be online most of time.
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That means users either have to be a bit tech-savvy to run their own node,
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or rely on someone else to run it for them.
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Currently, one of Status's legal entities provides `Mailservers` in an altruistic manner,
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but this is suboptimal from a decentralization, continuance and risk point of view.
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Coming up with a better system for this is ongoing research.
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A Status client SHOULD allow the `Mailserver` selection to be customizable.
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### Privacy concerns
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In order to use a `Mailserver`, a given node needs to connect to it directly,
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i.e. add the `Mailserver` as its peer and mark it as trusted.
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This means that the `Mailserver` is able to send direct p2p messages to the node instead of broadcasting them.
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Effectively, it will have access to the bloom filter of topics that the user is interested in,
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when it is online as well as many metadata like IP address.
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### Denial-of-service
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Since a `Mailserver` is delivering expired envelopes and has a direct TCP connection with the recipient,
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the recipient is vulnerable to DoS attacks from a malicious `Mailserver` node.
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## Changelog
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### Version 0.1
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Released [May 22, 2020](https://github.com/status-im/specs/commit/664dd1c9df6ad409e4c007fefc8c8945b8d324e8)
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* Created document
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* Forked from [whisper-mailserver](/status/deprecated/whisper-mailserver.md)
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* Change to keep `Mailserver` term consistent
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* Replaced Whisper references with Waku
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## Copyright
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Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
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## References
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* [May 22, 2020 change commit](https://github.com/status-im/specs/commit/664dd1c9df6ad409e4c007fefc8c8945b8d324e8)
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