  The problem of security of quantum key protocols is examined. In addition to
the distribution of classical keys, the problem of encrypting quantum data and
the structure of the operators which perform quantum encryption is studied. It
is found that unitary bases are central to both encryption of quantum
information, as well as the generation of states used in generalized quantum
key distribution (which are called mutually unbiased bases). A one-to-one
correspondence between certain unitary bases and mutually unbiased bases is
found. Finally, a new protocol for making anonymous classical broadcasts is
given along with a security proof. An experimental procedure to implement this
protocol is also given. In order to prove these new results, some new bounds
for accessible information of quantum sources are obtained.
