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Status Group Chat Specification

Version: 0.1 (Draft)

Authors: Andrea Maria Piana andreap@status.im

Abstract
Membership updates

Abstract

This documents describes the group chat protocol used by the status application. Pairwise encryption is used among member so a message is exchanged between each participants, similarly to a one-to-one message.

Membership updates

Membership updates messages are used to propagate group chat membership changes. The transit format is described in the Status Payload Specs. Here we will be describing each specific field.

The format is:

{
  "events": [struct {"type": string, "member": string, "members": [string], "clock-value": uint, "name": string],
  "signature": string,
  "chat-id": string
}

Chat ID

Each membership update MUST be sent with a corresponding chat-id. The format of this chat id MUST be a string, UUID, concatenated with the hex-encoded public key of the creator of the chat. This chat-id MUST be validated by all clients, and MUST be discarded if it does not follow these rules.

Signature

The signature for each event is calculated by creating a JSON array of all the events sorted by clock-value in ascending order, where each event is transformed in an array of tuples field-name, value, sorted by field-name in ascending alphabetical order. The last element of the array MUST be the chat-id. Empty fields MUST be removed.

For example the event:

   {
     "chat-id": "chat-id",
       "events":  [
       {"b": "b-value"
        "clock-value": 1,
        "a": "a-value"
        },
       {
         "e": "e-value",
         "clock-value": 0,
         "a": "a-value"
       }
       ]
   }

Results in the structure:

   [
     [
       [
         ["a" "a-value"],
         ["clock-value", 0],
         ["e" "e-value"]
       ],
       [
         ["a", "a-value"],
         ["b", "b-value"],
         ["clock-value", 1]
       ]
     ],
     "chat-id"
   ]

This structure is then stringified collapsing all whitespaces and the Keccak256 of the string is then signed using its private key by the author and added to the payload.

Group membership event

Any group membership event received MUST be verified by calculating the signature as per the method described above. The author MUST be extracted from it, if the verification fails the event MUST be discarded.

chat-created

{
  "type": "chat-created",
  "name": string
  "clock-value": uint
}

Chat created event is the first event that needs to be sent. Any event with a clock value lower then this MUST be discarded. Upon receiving this event a client MUST validate the chat-id provided with the updates and create a chat with identified by chat-id and named name.

name-changed

{
  "type": "name-changed"
  "name": string
  "clock-value": uint
}

A name changed event is used by admins to change the name of the group chat. Upon receiving this event a client MUST validate the chat-id provided with the updates and MUST ensure the author of the event is an admin of the chat, otherwise the event MUST be ignored. If the event is valid the chat name SHOULD be changed to name.

members-added

{
  "type": "members-added"
  "members": [string]
  "clock-value": uint
}

A members added event is used by admins to add members to the chat. Upon receiving this event a client MUST validate the chat-id provided with the updates and MUST ensure the author of the event is an admin of the chat, otherwise the event MUST be ignored. If the event is valid a client MUST update the list of members of the chat who have not joined, adding the members received. members is an array of hex encoded public keys.

member-joined

{
  "type": "member-joined"
  "member": string
  "clock-value": uint
}

A members joined event is used by a member of the chat to signal that they want to start receiving messages from this chat. Upon receiving this event a client MUST validate the chat-id provided with the updates and MUST ensure the author of the event is the same as the one specified by the member field. If the event is valid a client MUST update the list of members of the chat who joined, adding member. Any message sent to the group chat should now include the newly joined member.

admins-added

{
  "type": "admins-added"
  "members": [string]
  "clock-value": uint
}

An admins added event is used by admins to add make other admins in the chat. Upon receiving this event a client MUST validate the chat-id provided with the updates, MUST ensure the author of the event is an admin of the chat and MUST ensure all members are already members of the chat, otherwise the event MUST be ignored. If the event is valid a client MUST update the list of admins of the chat, adding the members received. members is an array of hex encoded public keys.

member-removed

{
  "type": "member-removed"
  "member": string
  "clock-value": uint
}

A member-removed event is used to leave or kick members of the chat. Upon receiving this event a client MUST validate the chat-id provided with the updates, MUST ensure that:

If the author of the event is an admin, target can only be themselves or a non-admin member.
If the author of the event is not an admin, the target of the event can only be themselves.

If the event is valid a client MUST remove the member from the list of members/admins of the chat, and no further message should be sent to them.

admin-removed

{
  "type": "admin-removed"
  "member": string
  "clock-value": uint
}

An admin-removed event is used to drop admin privileges. Upon receiving this event a client MUST validate the chat-id provided with the updates, MUST ensure that the author of the event is also the target of the event.

If the event is valid a client MUST remove the member from the list of admins of the chat.

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