+.TP
+.B tag-length-bytes
+The length of the message authentication tag. The default is 16,
+for a 128-bit tag length. It must be no longer than the Serpent
+blocksize, 16. Must be have the same value at both ends.
+.TP
+.B padding-rounding
+Messages are padded to a multiple of this many bytes. This
+serves to obscure the exact length of messages. The default is 16,
+.TP
+.B capab-num
+The transform capability number to use when advertising this
+transform. Both ends must have the same meaning (or, at least, a
+compatible transform) for each transform capability number they have
+in common. The default for serpent-eax is 9.
+.IP
+Transform capability numbers in the range 8..15 are intended for
+allocation by the implementation, and may be assigned as the default
+for new transforms in the future. Transform capability numbers in the
+range 0..7 are reserved for definition by the user.