Family key is symmetric

As I understand it, the Skipjack system is symmetric, i.e., decrypt key=
encrypt key.  Also, the unit serial number seems to only get encrypted
with the family key.

So, once the family key and the algorithm are known, it will be
possible to create messages with any unit serial number you want, right?

Wouldn't this be enough to foil the casual traffic-analysis feature
of the crippler?

--fnerd
the keyhole chip
the wing clipper
co-intel inside
as seen on whitehouse stationery
only open a crack
the taped lock
cyphergate
"Daffy, you quack me up." --Elmer