+x25519 \fInone
+x448 \fInone
+_
+.TE
+.ne 9
+.TP
+.I kx-attrs
+Additional attributes to set on the parameters
+(and therefore copied to peer keys),
+as
+.IB key = value
+pairs separated by spaces.
+Default depends on
+.I kx
+as follows.
+.TS
+center;
+| ci | ci |
+| lb | lb |.
+_
+kx kx-attrs
+_
+dh serialization=constlen
+ec serialization=constlen
+x25519 \fIempty
+x448 \fIempty