A data reproducing apparatus and method is provided for reproducing data that
ciphered during recording in one or more of sector forming, header appending, error
correction coding, modulation, and synchronization appending operations used for
processing input data to form a recording signal. Thus, deciphering requires knowledge
of both the ciphering key and the aspect(s) of the recording operation in which
the ciphering took place. The deciphering may also include a descrambling operation
in which an initial value and/or a generating polynomial is varied in accordance
with ciphering key information.