Implementing a Status clients largely means implementing the following layers. Additionally, there are separate specifications for things like key management and account lifecycle.
Other aspects, such as how IPFS is used for stickers, how we interact with the Ethereum blockchain or how the browser works, are currently underspecified. These sets of specifications should allow you to implement a a Status client for basic private communication.
A Status client MUST use at least one discovery method or use static nodes
to communicate with other clients.
Discovery V5 uses bootstrap nodes to discover other peers. Bootstrap nodes MUST support
Discovery V5 protocol as well in order to provide peers. It is kademlia-based discovery mechanism
and it might consume significant (at least on mobile) amount of network traffic to operate.
In order to take advantage from simpler and more mobile-friendly peers discovery mechanism,
i.e. Rendezvous protocol, one MUST provide a list of Rendezvous nodes which speak
Rendezvous protocol. Rendezvous protocol is request-response discovery mechanism.
It uses Ethereum Node Records (ENR) to report discovered peers.
Both peers discovery mechanisms use topics to provide peers with certain capabilities.
There is no point in returning peers that do not support a particular protocol.
Status nodes that want to be discovered MUST register to Discovery V5 and/or Rendezvous
with the `whisper` topic. Status nodes that are mail servers and want to
be discoverable MUST additionally register with the `whispermail` topic.
It is RECOMMENDED to use both mechanisms but at the same time implement a structure
called `PeerPool`. `PeerPool` is responsible for maintaining an optimal number of peers.
For mobile nodes, there is no significant advantage to have more than 2-3 peers and one mail server.
`PeerPool` can notify peers discovery protocol implementations that they should suspend
their execution because the optimal number of peers is found. They should resume
if the number of connected peers drops or a mail server disconnects.
It is worth noticing that an efficient caching strategy MAY be of great use, especially,
on mobile devices. Discovered peers can be cached as they rarely change and used
when the client starts again. In such a case, there might be no need to even start
peers discovery protocols because cached peers will satisfy the optimal number of peers.
Alternatively, a client MAY rely exclusively on a list of static peers. This is the most efficient
way because there is no peers discovery algorithm overhead introduced. The disadvantage
is that these peers might be gone and without peers discovery mechanism, it won't be possible to find
new ones.
The current list of static peers is published on <https://fleets.status.im/>. `eth.prod` is the current
group of peers the official Status client uses. The others are test networks.
#### Mobile nodes
This is a Whisper node which connects to part of the Whisper network. It MAY
relay messages. See next section for more details on how to use Whisper to
communicate with other Status nodes.
### Transport privacy and Whisper usage
Once a Whisper node is up and running there are some specific settings required
to commmunicate with other Status nodes.
See [Status Whisper Usage Spec](status-whisper-usage-spec.md) for more details.
For providing offline inboxing, see the complementary [Whisper Mailserver
Spec](status-whisper-mailserver-spec.md).
### Secure Transport
In order to provide confidentiality, integrity, authentication and forward
secrecy of messages we implement a secure transport on top of Whisper. This is
used in 1:1 chats and group chats, but not for public chats. See [Status Secure
Transport Spec](status-secure-transport-spec.md) for more.
### Data Sync
[MVDS](https://specs.vac.dev/mvds.html) is used for 1:1 and group chats, however it is currently not in use for public chats.
[Status payloads](#payloads-and-clients) are serialized and then wrapped inside a MVDS message which is added to an [MVDS payload](https://specs.vac.dev/mvds.html#payloads), this payload is then encrypted (if necessary for 1-to-1 / group-chats) and sent using whisper which also encrypts it.
### Payloads and clients
On top of secure transport, we have various types of data sync clients and
payload formats for things like 1:1 chat, group chat and public chat. These have
various degrees of standardization. Please refer to [Initial Message Payload
Specification](status-payloads-spec.md) for more details.
### BIPs and EIPs Standards support
For a list of EIPs and BIPs that SHOULD be supported by Status client, please
see [Status EIPs Standards](status-EIPs.md).
## Security Considerations
See [Appendix A](#appendix-a-security-considerations)
## Design Rationale
### P2P Overlay
#### Why devp2p? Why not use libp2p?
At the time the main Status clients were being developed, devp2p was the most
mature. However, it is likely we'll move over to libp2p in the future, as it'll
provide us with multiple transports, better protocol negotiation, NAT traversal,
etc.
For very experimental bridge support, see the bridge between libp2p and devp2p
in [Murmur](https://github.com/status-im/murmur).
#### What about other RLPx subprotocols like LES, and Swarm?
Status is primarily optimized for resource restricted devices, and at present
time light client support for these protocols are suboptimal. This is a work in
progress.
For better Ethereum light client support, see [Re-enable LES as
option](https://github.com/status-im/status-go/issues/1025). For better Swarm
#### I heard something about mailservers being trusted somehow?
In order to use a mail server, a given node needs to connect to it directly, i.e. add the mailserver as its peer and mark it as trusted. This means that the mail server is able to send direct p2p messages to the node instead of broadcasting them. Effectively, it knows the bloom filter of the topics the node is interested in, when it is online as well as many metadata like IP address.
### Data sync
#### Why is MVDS not used for public chats?
Currently public chats are broadcast-based, and there's no direct way of finding
out who is receiving messages. Hence there's no clear group sync state context
whereby participants can sync. Additionally, MVDS is currently not optimized for
large group contexts, which means bandwidth usage will be a lot higher than
reasonable. See [P2P Data Sync for
Mobile](https://vac.dev/p2p-data-sync-for-mobile) for more. This is an active
area of research. The bandwidth issue is further exacerbated by Whisper being
There are several security considerations to take into account when running Status. Chief among them are: scalability, DDoS-resistance and privacy. These also vary depending on what capabilities are used, such as mailserver, light node, and so on.
### Scalability and UX
**Bandwidth usage:**
In version 1 of Status, bandwidth usage is likely to be an issue. For more investigation into this, see [the theoretical scaling model](https://github.com/vacp2p/research/tree/dcc71f4779be832d3b5ece9c4e11f1f7ec24aac2/whisper_scalability).
**Mailserver High Availability requirement:**
A mailserver has to be online to receive messages for other nodes, this puts a high availability requirement on it.
**Gossip-based routing:**
Use of gossip-based routing doesn't necessarily scale. It means each node can see a message multiple times, and having too many light nodes can cause propagation probability that is too low. See [Whisper vs PSS](https://our.status.im/whisper-pss-comparison/) for more and a possible Kademlia based alternative.
**Lack of incentives:**
Status currently lacks incentives to run nodes, which means node operators are more likely to create centralized choke points.
### Privacy
**Light node privacy:**
The main privacy concern with light nodes is that directly connected peers will know that a message originates from them (as it are the only ones it sends). This means nodes can make assumptions about what messages (topics) their peers are interested in.
**Bloom filter privacy:**
By having a bloom filter where only the topics you are interested in are set, you reveal which messages you are interested in. This is a fundamental tradeoff between bandwidth usage and privacy, though the tradeoff space is likely suboptimal in terms of the [Anonymity](https://eprint.iacr.org/2017/954.pdf) [trilemma](https://petsymposium.org/2019/files/hotpets/slides/coordination-helps-anonymity-slides.pdf).
**Mailserver client privacy:**
A mailserver client has to trust a mailserver, which means they can send direct traffic. This reveals what topics / bloom filter a node is interested in, along with its peerID (with IP).
**Privacy guarantees not rigorous:**
Privacy for Whisper hasn't been studied rigorously for various threat models like global passive adversary, local active attacker, etc. This is unlike e.g. Tor and mixnets.
**Topic hygiene:**
Similar to bloom filter privacy, if you use a very specific topic you reveal more information. See scalability model linked above.
### Spam resistance
**PoW bad for heterogenerous devices:**
Proof of work is a poor spam prevention mechanism. A mobile device can only have a very low PoW in order not to use too much CPU / burn up its phone battery. This means someone can spin up a powerful node and overwhelm the network.
**Mailserver trusted connection:**
A mailserver has a direct TCP connection, which means they are trusted to send traffic. This means a malicious or malfunctioning mailserver can overwhelm an individual node.
### Censorship resistance
**Devp2p TCP port blockable:**
By default Devp2p runs on port `30303`, which is not commonly used for any other service. This means it is easy to censor, e.g. airport WiFi. This can be mitigated somewhat by running on e.g. port `80` or `443`, but there are still outstanding issues. See libp2p and Tor's Pluggable Transport for how this can be improved.
See <https://github.com/status-im/status-react/issues/6351> for some discussion.
