typedef void (*SilcSKECompletionCb)(SilcSKE ske,
                                        SilcSKEStatus status,
                                        const SilcSKESecurityProperties prop,
                                        const SilcSKEKeyMaterial keymat,
                                        SilcSKERekeyMaterial rekey,
                                        void *context);

    Completion callback.  This is called after the key exchange protocol
    has been completed.  It delivers the status of the protocol, and if
    successful the security properties `prop' that was negotiated in the
    protocol and the key material `keymat' that can be set into use by
    calling silc_ske_set_keys, and the rekey key material `rekey' which
    can be used later to start rekey protocol.  The `prop' and `keymat'
    will remain valid as long as `ske' is valid.  The `rekey' will remain
    valid until silc_ske_free_rekey_material is called.  The application
    must call it to free the `rekey'.

    When doing rekey, this completion callback delivers the `keymat' and
    new `rekey'.  The `prop' is ignored.  The `keymat' has already been set
    to the packet stream associated with the `ske'.  Thus, after this
    is called the new keys are in use.