code: OmemoMessage.Sent createKeyTransportElement(OmemoManager.LoggedInOmemoManager managerGuard,
                                                  Set<OmemoDevice> contactsDevices,
                                                  byte[] key,
                                                  byte[] iv)
              throws InterruptedException, UndecidedOmemoIdentityException, CryptoFailedException,
              SmackException.NotConnectedException, SmackException.NoResponseException {
          return encrypt(managerGuard, contactsDevices, key, iv, null);
      }
docs: Create an OMEMO KeyTransportElement.
  @see <a href="https://xmpp.org/extensions/xep-0384.html#usecases-keysend">XEP-0384: Sending a key</a>.
  
  @param managerGuard Initialized OmemoManager.
  @param contactsDevices set of recipient devices.
  @param key AES-Key to be transported.
  @param iv initialization vector to be used with the key.
  @return KeyTransportElement
  
  @throws InterruptedException
  @throws UndecidedOmemoIdentityException if the list of recipients contains an undecided device
  @throws CryptoFailedException if we are lacking some cryptographic algorithms
  @throws SmackException.NotConnectedException
  @throws SmackException.NoResponseException