+/* --- @VALIDP@ --- *
+ *
+ * Arguments: @const keyexch *kx@ = key exchange state
+ * @time_t now@ = current time in seconds
+ *
+ * Returns: Whether the challenge in the key-exchange state is still
+ * valid or should be regenerated.
+ */
+
+#define VALIDP(kx, now) ((now) < (kx)->t_valid)
+