+#define CAPAB_EARLY 0x00000000 /* no Early flags yet (see NOTES) */
+#define CAPAB_TRANSFORM_MASK 0x0000ffff
+/* remaining 16 bits are unused */
+
+/*
+ * The transform capability mask is a set of bits, one for each
+ * transform supported. The transform capability numbers are set in
+ * the configuration (and should correspond between the two sites),
+ * although there are sensible defaults.
+ *
+ * Advertising a nonzero transform capability mask promises that
+ * the receiver understands LABEL_MSG3BIS messages, which
+ * contain an additional byte specifying the transform capability
+ * number actually chosen by the MSG3 sender.
+ *
+ * Aside from that, an empty bitmask is treated the same as
+ * 1u<<CAPAB_TRANSFORMNUM_ANCIENT
+ */
+
+/* bit indices, 0 is ls bit */
+#define CAPAB_TRANSFORMNUM_USER_MIN 0
+#define CAPAB_TRANSFORMNUM_USER_MAX 7
+#define CAPAB_TRANSFORMNUM_SERPENT256CBC 8
+#define CAPAB_TRANSFORMNUM_EAXSERPENT 9
+#define CAPAB_TRANSFORMNUM_MAX 15
+
+#define CAPAB_TRANSFORMNUM_ANCIENT CAPAB_TRANSFORMNUM_SERPENT256CBC