Method external_join

mlspp/src/state.cpp:282–330

}

std::tuple<MLSMessage, State>
State::external_join(const bytes& leaf_secret,
                     SignaturePrivateKey sig_priv,
                     const KeyPackage& key_package,
                     const GroupInfo& group_info,
                     const std::optional<TreeKEMPublicKey>& tree,
                     const MessageOpts& msg_opts,
                     std::optional<LeafIndex> remove_prior,
                     const std::map<bytes, bytes>& psks)
{
  // Create a preliminary state
  auto initial_state = State(std::move(sig_priv), group_info, tree);

  // Look up the external public key for the group
  const auto maybe_external_pub =
    group_info.extensions.find<ExternalPubExtension>();
  if (!maybe_external_pub) {
    throw InvalidParameterError("No external pub in GroupInfo");
  }

  const auto& external_pub = opt::get(maybe_external_pub).external_pub;

  // Insert an ExternalInit proposal
  auto opts = CommitOpts{};
  auto [enc, force_init_secret] =
    KeyScheduleEpoch::external_init(key_package.cipher_suite, external_pub);
  auto ext_init = Proposal{ ExternalInit{ enc } };
  opts.extra_proposals.push_back(ext_init);

  // Evict a prior appearance if required
  if (remove_prior) {
    auto remove = initial_state.remove_proposal(opt::get(remove_prior));
    opts.extra_proposals.push_back(remove);
  }

  // Inject PSKs
  for (const auto& [id, secret] : psks) {
    initial_state.add_external_psk(id, secret);
    auto psk = initial_state.pre_shared_key_proposal(id);
    opts.extra_proposals.push_back(psk);
  }

  // Use the preliminary state to create a commit and advance to a real state
  auto params = ExternalCommitParams{ key_package, force_init_secret };
  auto [commit_msg, welcome, state] =
    initial_state.commit(leaf_secret, opts, msg_opts, params);
  silence_unused(welcome);
  return { commit_msg, state };
}

MLSMessage
State::new_member_add(const bytes& group_id,