Group conversations

Group chats use the same encryption model as 1:1 X Chat: one conversation key shared by members, wrapped to each member’s identity public key, with messages encrypted and signed by the Chat XDK. What changes is membership, how you create the thread, and often encrypted title/avatar fields on the conversation. 1:1 flows are in Getting Started. Endpoint details are under API reference → Conversations and messages.

How groups differ from 1:1

Topic	1:1	Group
Identity	Often addressed by peer user id in paths	Conversation id typically starts with `g`
Create	Keys + messaging to a user	Create / initialize group APIs, then keys
Participants	You + one peer	Many users; membership can change
Metadata	Minimal	Name, avatar, etc. may be ciphertext (decrypt with the conversation key)
Key rotation	Less frequent	Common when people join or leave

Crypto is still: Chat XDK for keys and payloads; X API to create the group, publish participant key wraps, send messages, and load events.

Create the group and establish keys

Mint the group id with POST /2/chat/conversations/group/initialize — the response’s data.conversation_id is the g-prefixed id you use everywhere below.
Load each member’s identity public key and public_key_version (GET public-key routes under Encryption keys; GET /2/users/public_keys fetches several users in one request). Verify each record with verify_key_binding before using it (see the warning in Getting Started).
Run prepare_group_create once, with all members (including yourself), the g-prefixed id, and the member/admin id lists. One call generates the conversation key, wraps it for every member, and signs the create — it returns two action signatures (the conversation-key change and the group create).
POST /2/chat/conversations/group with the group members/admins, conversation_key_version, conversation_participant_keys (SDK encrypted_key → API encrypted_conversation_key), and both action_signatures. Validation failures come back as stable, human-readable messages, for example "Too many members: adding these members would exceed the allowed group size." or "Cannot add all members: one or more of the requested members cannot be added to this conversation.".
Keep the raw conversation key and version for encrypt/decrypt.

prepare_group_create signs the title and avatar_url you pass in and embeds them verbatim in the group-create event. The server matches those against your request, so the group_name / group_avatar_url values in the POST body must be byte-identical to what you passed the SDK — otherwise the call fails signature validation.

prepared = chat.prepare_group_create(
    "YOUR_USER_ID", signing_key_version, member_public_keys,
    group_id,  # g-prefixed id from POST /2/chat/conversations/group/initialize
    member_ids, admin_ids, title="Project team",
)
# POST /2/chat/conversations/group with group_members, group_admins,
# conversation_key_version, conversation_participant_keys, and BOTH
# entries of prepared["action_signatures"]

const prepared = chat.prepareGroupCreate({
  senderId: myUserId, signingKeyVersion, publicKeys: memberPublicKeys,
  conversationId: groupId, // g-prefixed id from POST /2/chat/conversations/group/initialize
  memberIds, adminIds, title: 'Project team',
});
// prepared.actionSignatures has two entries — send both

let mut params = GroupCreateParams::new(
    &sender_id, &signing_key_version, member_public_keys,
    &group_id, member_ids, admin_ids,
);
params.title = Some("Project team".into());
let prepared = chat.prepare_group_create(params)?;
// prepared.action_signatures has two entries — send both

prepared, err := chat.PrepareGroupCreate(chatxdk.GroupCreateParams{
    SenderID: myUserID, SigningKeyVersion: signingKeyVersion,
    PublicKeys: memberPublicKeys, ConversationID: groupID,
    MemberIDs: memberIDs, AdminIDs: adminIDs, Title: "Project team",
})
// prepared.ActionSignatures has two entries — send both
_ = prepared
_ = err

var prepared = chat.PrepareGroupCreate(new GroupCreateParams {
    SenderId = myUserId, SigningKeyVersion = signingKeyVersion,
    PublicKeys = memberPublicKeys, ConversationId = groupId,
    MemberIds = memberIds, AdminIds = adminIds, Title = "Project team",
});
// prepared.ActionSignatures has two entries — send both

GroupCreateParams params = new GroupCreateParams();
params.senderId = myUserId;
params.signingKeyVersion = signingKeyVersion;
params.publicKeys = memberPublicKeys;
params.conversationId = groupId;
params.memberIds = memberIds;
params.adminIds = adminIds;
params.title = "Project team";
PreparedConversationChange prepared = chat.prepareGroupCreate(params);
// prepared.actionSignatures has two entries — send both

The body mapping for participant keys and action signatures (message_id, encoded_message_event_detail, nested message_event_signature) is the same as the keys POST in Getting Started — conversation keys. When membership changes, call prepare_group_members_change with the new member ids plus the current roster (members, admins, pending members, and the current title/avatar/TTL if set). It rotates the conversation key and, like group create, returns two action signatures — POST all of it to add members (POST /2/chat/conversations/{id}/members). Then expect key-change traffic: treat it like key rotation in Getting Started (extract_conversation_keys / decrypt_events, then encrypt with the latest version). Because prepare_group_members_change generates a fresh conversation key wrapped only to the roster you pass, new members receive the new key version and cannot decrypt messages sent under earlier versions. The reverse is not true: rotation never revokes access to earlier versions — anyone who already holds an old key can still read the messages encrypted under it. If you suspect a conversation key was exposed, rotate with prepare_conversation_key_change; this protects future messages only.

Encrypted group metadata

Some conversation fields (for example display name or avatar URL) may arrive encrypted under the conversation key. That is not encrypt_message; it is the generic Chat XDK encrypt / decrypt pair (UTF-8 string in, base64 ciphertext out, with the raw conversation key). Whether a given field is stored encrypted is decided by the client that writes it: prepare_group_create signs and sends the title exactly as you provide it (the conversation key does not exist until that call generates it, so a create-time title cannot be encrypted under it). When you read a conversation whose fields are ciphertext, decrypt them with decrypt and the key version that was active when the field was written.

# Decrypt a field from the conversation object (name may vary by API shape)
group_name = chat.decrypt(conversation["group_name"], raw_conv_key)

# Encrypt before update if your API accepts ciphertext metadata
encrypted_name = chat.encrypt("Project team", raw_conv_key)

const groupName = chat.decrypt(conversation.groupName, rawConvKey);
const encryptedName = chat.encrypt('Project team', rawConvKey);

// conv_key: &XChatConversationKey from extract_conversation_keys / decrypt_conversation_key
let group_name = chat.decrypt(&conversation_group_name_b64, &conv_key)?;
let encrypted_name = chat.encrypt("Project team", &conv_key)?;

groupName, err := chat.Decrypt(conversationGroupNameB64, rawConvKey)
encryptedName, err := chat.Encrypt("Project team", rawConvKey)
_ = groupName
_ = encryptedName

string groupName = chat.Decrypt(conversationGroupNameB64, rawConvKey);
string encryptedName = chat.Encrypt("Project team", rawConvKey);

String groupName = chat.decrypt(conversationGroupNameB64, rawConvKey);
String encryptedName = chat.encrypt("Project team", rawConvKey);

Use the current conversation key version that applies to that metadata. If keys rotated, decrypt with the version that was active when the field was written (or follow product rules if metadata is always rewritten on rotation).

Messages and events

Sending and receiving in a group is the same as 1:1 once you have the raw conversation key:

Send: encrypt_message → send-message API (Getting Started)
Receive: events API or real-time delivery → decrypt_event / decrypt_events
Media: Media with the group conversation id

Always encrypt with the latest key version after a membership-driven rotation.

Checklist

Mint the g-prefixed id with POST /2/chat/conversations/group/initialize
prepare_group_create with every member; POST participant key wraps and both action signatures to POST /2/chat/conversations/group
Cache raw key + version; update on key-change events
On membership changes, prepare_group_members_change (two signatures) → POST /2/chat/conversations/{id}/members
Decrypt group metadata with decrypt when fields are ciphertext
Send/receive with the same patterns as 1:1

​How groups differ from 1:1

​Create the group and establish keys

​Encrypted group metadata

​Messages and events

​Checklist

How groups differ from 1:1

Create the group and establish keys

Encrypted group metadata

Messages and events

Checklist