10 KiB
Status Client Specification
Version: 0.1 (Draft)
Authors: Adam Babik adam@status.im, Dean Eigenmann dean@status.im, Oskar Thorén oskar@status.im (alphabetical order)
Table of Contents
Abstract
In this specification, we describe how to write a Status client for communicating with other Status clients.
We present a reference implementation of the protocol 1 that is used in a command line client 2 and a mobile app 3.
This document consists of two parts. The first outlines the specifications that have to be implemented in order to be a full Status client.
P2P Overlay
Status clients run on the public Ethereum network, as specified by the devP2P network protocols. devP2P provides a protocol for node discovery which is in draft mode here. See more on node discovery and management in the next section.
To communicate between Ethereum nodes, the RLPx Transport Protocol, v5 is used, which allows for TCP-based communication between nodes.
On top of this we run the RLPx-based subprotocol Whisper v6 for privacy-preserving messaging.
Node discovery and roles
There are four types of node roles:
- Bootstrap nodes
- Whisper relayers
- Mailservers (servers and clients)
- Mobile nodes (Status Clients)
To implement a standard Status client you MUST implement the last node type. The other node types are optional, but we RECOMMEND you implement a mailserver client mode, otherwise the user experience is likely to be poor.
Bootstrapping
To connect to other Status nodes you need to connect to a bootstrap node. These nodes allow you to discover other nodes of the network.
Currently the main bootstrap nodes are provided by Status Gmbh, but anyone can run these provided they are connected to the rest of the Whisper network.
Discovery
To implement a Status client you need to discover peers to connect to. We use a light discovery mechanism based on a combination of Discovery v5 and Rendezvous Protocol, (with some modifications). Additionally, some static nodes MAY also be used.
This part of the system is currently underspecified and requires further detail.
Mailservers
Whisper Mailservers are special nodes that helps with offline inboxing. This means you can receive Whisper envelopes after they have expired, which is useful if they are sent while a node is offline. They operate on a store-and-forward model.
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.
Whisper adapter
Once a Whisper node is up and running there are some specific settings required to commmunicate with other Status nodes.
Node configuration
Whisper's Proof Of Work algorithm is used to deter denial of service and various spam/flood attacks against the Whisper network. The sender of a message must perform some work which in this case means processing time. Because Status' main client is a mobile client, this easily leads to battery draining and poor erformance of the app itself. Hence, all clients MUST use the following Whisper node settings:
- proof-of-work not larger than
0.002 - time-to-live not lower than
10(in seconds)
Keys management and encryption
The protocol requires a key (symmetric or asymmetric) for the following actions:
- signing a message (a private key)
- decrypting received messages (a private key or symmetric key).
As private keys and symmetric keys are required to process incoming messages, they must be available all the time and are stored in memory.
All encryption algorithms used by Whisper are described in the Whisper V6 specification.
Symmetric keys are created using
shh_generateSymKeyFromPassword
Whisper V6 RPC API method which accepts one param, a string.
Messages encrypted with asymmetric encryption should be encrypted using recipient's public key so that only the recipient can decrypt them.
Key management and encryption for conversational security is described in Conversational Security, which provides properties such as forward secrecy.
Topics
There are two types of Whisper topics the protocol uses:
- static topic for
user-messagemessage type (also called contact discovery topic) - dynamic topic based on a chat name for
public-group-user-messagemessage type.
The static topic is always the same and its hex representation is 0xf8946aac.
In fact, the contact discovery topic is calculated using a dynamic topic
algorithm described below with a constant name contact-discovery.
Having only one topic for all private chats has an advantage as it's very hard to figure out who talks to who. A drawback is that everyone receives everyone's messages but they can decrypt only these they have private keys for.
A dynamic topic is derived from a string using the following algorithm:
var hash []byte
hash = keccak256(name)
# Whisper V6 specific
var topic [4]byte
topic_len = 4
if len(hash) < topic_len {
topic_len = len(hash)
}
for i = 0; i < topic_len; i++ {
topic[i] = hash[i]
}
Secure Transport
Data Sync
Payloads and clients
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.
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. For better Swarm support, see Swarm adaptive nodes.
For transaction support, Status clients currently have to rely on Infura.
Status clients currently do not offer native support for file storage.
Why do you use Whisper?
Whisper is one of the three parts of the vision of Ethereum as the world computer, Ethereum and Swarm being the other two. Status was started as an encapsulation of and a clear window to this world computer.
I heard you were moving away from Whisper?
Whisper is not currently under active development, and it has several drawbacks. Among others:
- It is very wasteful bandwidth-wise and it doesn't appear to be scalable
- Proof of work is a poor spam protection mechanism for heterogenerous devices
- The privacy guarantees provided are not rigorous
- There's no incentives to run a node
Finding a more suitable transport privacy is an ongoing research effort, together with Vac and other teams in the space.
Why is PoW for Whisper set so low?
A higher PoW would be desirable, but this kills the battery on mobilephones, which is a prime target for Status clients.
This means the network is currently vulnerable to DDoS attacks. Alternative methods of spam protection are currently being researched.
Why do you not use Discovery v5 for node discovery?
At the time we implemented dynamic node discovery, Discovery v5 wasn't completed yet. Additionally, running a DHT on a mobile leads to slow node discovery, bad battery and poor bandwidth usage. Instead, each client can choose to turn on Discovery v5 for a short period of time until their peer list is populated.
For some further investigation, see here.
Footnotes
- https://github.com/status-im/status-protocol-go/
- https://github.com/status-im/status-console-client/
- https://github.com/status-im/status-react/