# Messenger

The GNUnet Messenger subsystem allows decentralized message-based communication inside of so called rooms. Each room can be hosted by a variable amount of peers. Every member of a room has the possibility to host the room on its own peer. A peer allows any amount of members to join a room. The amount of members in a room is not restricted.

Messages in a room will be distributed between all peers hosting the room or being internally (in context of the messenger service) connected to a hosting peer. All received or sent messages will be stored on any peer locally which is hosting the respective room or is internally connected to such a hosting peer.

The Messenger service is built on the CADET subsystem to make internal connections between peers using a reliable and encrypted transmission. Additionally the service uses a discrete padding to few different sizes. So kinds of messages and potential content can’t be identified by the size of traffic from any attacker being unable to break the encryption of the transmission layer.

Another feature is additional end-to-end encryption for selected messages which uses the public key of another member (the receiver) to encrypt the message. Therefore it is ensured that only the selected member can read its content. This will also use additional padding.

## Current state

Currently there is only a simplistic CLI application available to use the messenger service. You can use this application with the `gnunet-messenger` command.

This application was designed for testing purposes and it does not provide full functionality in the current state. It is planned to replace this CLI application in later stages with a fully featured one using a client-side library designed for messenger applications.

## Entering a room

You can enter any room by its ROOMKEY and any PEERIDENTITY of a hosting peer. Optionally you can provide any IDENTITY which can represent a local ego by its name. This will automatically select that ego’s private key to sign your messages with.

    $ gnunet-messenger [-e IDENTITY] -d PEERIDENTITY -r ROOMKEY

A PEERIDENTITY gets entered in encoded form. You can get your own peer ID by using the `gnunet-peerinfo` command:

    $ gnunet-peerinfo -s

A ROOMKEY gets entered in readable text form. The service will then hash the entered ROOMKEY and use the result as shared secret for transmission through the CADET submodule. You can also optionally leave out the ‘-r’ parameter and the ROOMKEY to use the zeroed hash instead.

If no IDENTITY is provided you will not send any name to others, you will be referred as "anonymous" instead and use the anonymous ego (a shared key pair known to all peers). If you provide any IDENTITY a matching ego will be used to sign your messages. If there is no matching ego you will use the anonymous ego instead. The provided IDENTITY will be distributed as your name for the service in any case.

## Opening a room

You can open any room in a similar way to entering it. You just have to leave out the ‘-d’ parameter and the PEERIDENTITY of the hosting peer.

    $ gnunet-messenger [-e IDENTITY] -r ROOMKEY

Providing ROOMKEY and IDENTITY is identical to entering a room. Opening a room will also make your peer to a host of this room. So others can enter the room through your peer if they have the required ROOMKEY and your peer ID.

If you want to use the zeroed hash as shared secret key for the room you can also leave it out as well:

    $ gnunet-messenger

## Messaging in a room

Once joined a room by entering it or opening it you can write text-based messages which will be distributed between all internally conntected peers. All sent messages will be displayed in the same way as received messages.

This relates to the internal handling of sent and received messages being mostly identical on application layer. Every handled message will be represented visually depending on its kind, content and sender. A sender can usually be identified by the encoded member ID or their name.

    [17X37K] * 'anonymous' says: "hey"

## Private messaging

As referred in the introduction the service allows sending private messages with additional end-to-end encryption. These messages will be visually represented by messages of the kind ‘PRIVATE’ in case they can’t be decrypted with your used private key. Members who can’t decrypt the message can potentially only identify its sender but they can’t identify its receiver. This prevents other members from collecting more metadata than necessary about you.

    [17X37K] ~ message: PRIVATE

If they can be decrypted they will appear as their secret message instead but marked visually.

    [17X37K] ** 'anonymous' says: "hey"

Currently you can only activate sending such encrypted text messages instead of usual text messages by adding the ‘-p’ parameter:

    $ gnunet-messenger [-e IDENTITY] -d PEERIDENTITY -r ROOMKEY -p

Notice that you can only send such encrypted messages to members who use a private key which is not publicly known via the anonymous ego to ensure transparency. If any user could decrypt these messages they would not be private. So as receiver of such messages the IDENTITY is required and it has to match a local ego.