An apparatus and a method for encoding and decoding key data are provided. An
apparatus for encoding DPCMed differential data of key data includes a DND operator
which performs on input differential data a predetermined number of times a DND
operation, in which a divide operation is performed on the input differential data
so as to divide differential data belonging to a positive number region into halves
and so as to convert one half of the differential data belonging to an upper range
than the other half into negative values, and either a divide-up operation or a
divide-down operation is selectively performed on the results of the divide operation
depending on the range of the results of the divide operation so as to reduce the
range of differential data belonging to a negative number region or the positive
number region, respectively, a shift-up operator which performs a shift-up operation
on the results of the DND operation so as to transfer the differential data having
been through the DND operation to either the positive or negative number region,
a differential data selector which selectively outputs either the differential
data having been through the DND operation or the differential data having been
through the shift-up operation, and an entropy encoder which entropy-encodes the
differential data selected by the differential data selector.