SimpleX chat prototype is a thin terminal UI on top of [SimpleXMQ](https://github.com/simplex-chat/simplexmq) message broker that uses [SMP protocols](https://github.com/simplex-chat/simplexmq/blob/master/protocol).
This is WIP implementation of SimpleX chat that implements a new network topology for asynchronous communication combining the advantages and avoiding the disadvantages of federated and P2P networks.
If you expect a software being reliable most of the time and doing something useful, then this is probably not ready for you yet. We do use it for terminal chat though, and it seems to work most of the time - we would really appreciate if you try it and give us your feedback.
**Please note:** The main differentiation of SimpleX network is the approach to internet message routing rather than encryption; for that reason no sufficient attention was paid to either TCP transport level encryption or to E2E encryption protocols - they are implemented in an ad hoc way based on RSA and AES algorithms. See [SMP protocol](https://github.com/simplex-chat/simplexmq/blob/master/protocol/simplex-messaging.md#appendix-a) on TCP transport encryption protocol (AEAD-GCM scheme, with an AES key negotiation based on RSA key hash known to the client in advance) and [this section](https://github.com/simplex-chat/simplexmq/blob/master/rfcs/2021-01-26-crypto.md#e2e-encryption) on E2E encryption protocol (an ad hoc hybrid scheme a la PGP). These protocols will change in a consumer ready version to something more robust.
## Network topology
SimpleX is a decentralized client-server network that uses redundant, disposable nodes to asynchronously pass the messages via message queues, providing receiver and sender anonymity.
Unlike P2P networks, all messages are passed through one or several (for redundancy) servers, that do not even need to have persistence (in fact, the current [SMP server implementation](https://github.com/simplex-chat/simplexmq#smp-server) uses in-memory message storage, persisting only the queue records) - it provides better metadata protection than P2P designs, as no global participant ID is required, and avoids many [problems of P2P networks](https://github.com/simplex-chat/simplex-chat/blob/master/simplex.md#comparison-with-p2p-messaging-protocols).
Unlike federated networks, the participating server nodes do NOT have records of the users, do NOT communicate with each other, do NOT store messages after they are delivered to the recipients, and there is no way to discover the full list of participating servers - it avoids the problem of metadata visibility that federated networks suffer from and better protects the network, as servers do not communicate with each other. Each server node provides unidirectional "dumb pipes" to the users, that do authorization without authentication, having no knowledge of the the users or their contacts. Each queue is assigned two RSA keys - one for receiver and one for sender - and each queue access is authorized with a signature created using a respective key's private counterpart.
The routing of messages relies on the knowledge of client devices how user contacts and groups map at any given moment of time to these disposable queues on server nodes.
- Auto-populated recipient name - just type your messages to reply to the sender once the connection is established.
- Demo SMP server available at `smp1.simplex.im:5223` - you can deploy your own server (`smp-server` executable in [simplexmq](https://github.com/simplex-chat/simplexmq) repo).
- No global identity or any names visible to the server(s), ensuring full privacy of your contacts and conversations.
- E2E encryption, with RSA public key that has to be passed out-of-band (see [How to use SimpleX chat](#how-to-use-simplex-chat)).
- Message signing and verification with automatically generated RSA keys.
- Message integrity validation (via including the digests of the previous messages).
- Authentication of each command/message by SMP servers with automatically generated RSA key pairs.
RSA keys are not used as identity, they are randomly generated for each contact. 2048 bit keys are used, it can be changed to 4096-bit in code via [rsaKeySize setting](https://github.com/simplex-chat/simplex-chat/blob/master/apps/dog-food/Main.hs).
Download the chat binary for your system from the [latest stable release](https://github.com/simplex-chat/simplex-chat/releases) and make it executable as shown below.
On Linux, you can build the chat executable using [docker build with custom output](https://docs.docker.com/engine/reference/commandline/build/#custom-build-outputs):
> **Please note:** If you encounter ``version `GLIBC_2.28' not found`` error, rebuild it with `haskell:8.8.4-stretch` base image (change it in your local [Dockerfile](Dockerfile)).
By default, app data directory is created in the home directory (`~/.simplex`, or `%APPDATA%/simplex` on Windows), and SQLite database file `smp-chat.db` is initialized in it.
The default SMP server is `smp1.simplex.im#pLdiGvm0jD1CMblnov6Edd/391OrYsShw+RgdfR0ChA=` (base-64 encoded string after server host is the transport key digest) - it is pre-configured in the app.
The base-64 encoded string in server address is the digest of RSA transport handshake key that the server will generate on the first run and output its digest.
You can still talk to people using default or any other server - it only affects the location of the message queue when you initiate the connection (and the reply queue can be on another server, as set by the other party's client).
Once you have started the chat, use `/add <name1>` to create a new connection and generate an invitation (`<name1>` is any name you want to use for that contact). The add command will output an invitation. Send this invitation to your contact via any other channel.
The invitation has the format `smp::<server>::<queue_id>::<rsa_public_key_for_this_queue_only>`. The invitation can only be used once and even if this is intercepted, the attacker would not be able to use it to send you the messages via this queue once your contact confirms that the connection is established.
The contact who received the invitation should use `/connect <name2> <invitation>` to accept the connection (`<name2>` is any name that the accepting contact wants to use for you).
They would then use `@<name> <message>` commands to send messages. One may also press Space or just start typing a message to send a message to the contact that was the last.
SimpleX chat stores all your contacts and conversations in a local database file, making it private and portable by design, fully owned and controlled by you.
> **Please note:** SQLite foreign key constraints are disabled by default, and must be **[enabled separately for each database connection](https://sqlite.org/foreignkeys.html#fk_enable)**. The latter can be achieved by running `PRAGMA foreign_keys = ON;` command on an open database connection. By running data altering queries without enabling foreign keys prior to that, you may risk putting your database in an inconsistent state.
The consumer ready system will have these parts implemented:
1. Application level chat protocol. This will allow to separate physical server connection management from logical chat contacts, and to support all common chat functions. Currently in progress in [v4 branch](https://github.com/simplex-chat/simplex-chat/tree/v4).
2. Symmetric groups support in SMP agent protocol, as a foundation for chat groups.
3. SMP queue redundancy and rotation in SMP agent protocol.
4. Message delivery confirmation in SMP agent protocol.
5. Multi-agent/device data synchronization - to use chat on multiple devices.
8. Scripts for simple SMP server deployment to hosting providers: Linode ([done](https://github.com/simplex-chat/simplexmq#deploy-smp-server-on-linode)), Digital Ocean and Heroku.
10. Optional public contact/group addresses using DNS-based contact addresses (like email) to establish connections, but not using it to route messages - in this way you will keep all your contacts and groups even if you lose the control of the domain.
