+.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,