Updating own leaf node

Immediate operation

Members can update their own leaf node atomically with the .self_update() function. By default, only the HPKE encryption key is updated. The application can however also provide more parameters like a new credential, capabilities and extensions using the LeafNodeParameters struct.

    let (mls_message_out, welcome_option, _group_info) = bob_group
        .self_update(provider, &bob_signature_keys, LeafNodeParameters::default())
        .expect("Could not update own key package.")
        .into_contents();

The function returns a CommitMessageBundle, which consists of the Commit message that needs to be fanned out to existing group members. Even though the member updates its own leaf node only in this operation, the Commit message could potentially also cover Add Proposals that were previously received in the epoch. Therefore the CommitMessagBundle can also contain a Welcome message. The Welcome message must be sent to the newly added members.

Members can use the .self_update_with_new_signer() function to also update the Signer used to sign future MLS messages.

    let new_signer_bundle = NewSignerBundle {
        signer: &alice_new_signature_keys,
        credential_with_key: alice_new_credential,
    };

    let message_bundle = alice_group
        .self_update_with_new_signer(
            provider,
            &alice_old_signature_keys,
            new_signer_bundle,
            LeafNodeParameters::default(),
        )
        .unwrap();

    let (mls_message_out, welcome, group_info) = message_bundle.into_contents();

When constructing the NewSignerBundle, the Signer must match the public key and credential in the CredentialWithKey. When using self_update_with_new_signer, LeafNodeParameters may not contain a CredentialWithKey.

Proposal

Members can also update their leaf node as a proposal (without the corresponding Commit message) by using the .propose_self_update() function. Just like with the .self_update() function, optional parameters can be set through LeafNodeParameters:

    let (mls_message_out, _proposal_ref) = alice_group
        .propose_self_update(
            provider,
            &alice_signature_keys,
            LeafNodeParameters::default(),
        )
        .expect("Could not create update proposal.");

In this case, the function returns an MlsMessageOut that needs to be fanned out to existing group members.