SilcSKEStatus silc_ske_responder_start(SilcSKE ske, SilcRng rng,
                                           SilcSocketConnection sock,
                                           const char *version,
                                           SilcBuffer start_payload,
                                           SilcSKESecurityPropertyFlag 
                                                               flags);

    Starts Key Exchange protocol for responder. The application has
    received initiator's first packet from network and it must provide
    it as `start_payload' argument to this function. The function 
    processes the packet and makes security property selection from
    the initiator's proposal. The `version' is the responder's version
    that will be sent in reply to the initiator. The `flags' indicates
    SilcSKESecurityPropertyFlag flags that responder enforces for the
    initiator. Responder may, for example, enforce that the PFS
    will be performed in rekey. This example can be done by providing
    SILC_SKE_SP_FLAG_PFS as `flags'. The `flags' is a bit mask of
    enforced flags.

    After this function the responder calls immediately, or with short
    timeout the silc_ske_responder_phase_1 function.