+size_t zg_group(ZG* zg, unsigned char *dst, unsigned char src);
+
+/** Termina de obtener ceros agrupados por zg_group(), si los hubiera.
+ * FIXME */
+size_t zg_group_finish(ZG* zg, unsigned char *dst);
+
+/** Vuelve al original. FIXME */
+size_t zg_ungroup(ZG* zg, unsigned char *dst, unsigned char src);