There are disclosed an extended key generator, encryption/decryption unit,
and storage medium, in which as each of key transform functions, a transform process
is done by an S box (substitution table) on the basis of a first key obtained from
the inputted key, and an adder computes a corresponding one of extended keys on
the basis of a value obtained by shifting the transformed result of the S box to
the left, and a second key obtained from the inputted key.
