SilcAsyncOperation
    silc_ske_responder(SilcSKE ske,
                       SilcPacketStream stream,
                       SilcSKEParams params);

    Starts SILC Key Exchange protocol as responder.  The completion
    callback that was set in silc_ske_set_callbacks will be called once
    the protocol has completed.  The `stream' is the network connection
    to the remote host.  The SKE library will handle all key exchange
    packets sent and received in the `stream' connection.  The library will
    also set the remote hosts's ID automatically to the `stream' if it is
    present in the exchanged packets.  The `params' include SKE parameters,
    and must be provided.

    This function returns SilcAsyncOperation operation context which can
    be used to control the protocol from the application.  Application may
    for example safely abort the protocol at any point, if needed.  Returns
    NULL on error.