Encryption apparatus and computor-readable recording medium containing program for realizing the same

A recording medium including a recorded computer readable program for operating an encryption apparatus for generating a ciphertext string corresponding to a plaintext string of a plaintext based on an encryption key:

• wherein said apparatus comprising:
• at least one conversion means for performing linear or non-linear conversion of the bit string;
• an intermediate-key generating means for generating an initial-value of the intermediate-key after performing linear or non-linear conversion for an inputted intermediate-key;
• and
• an intermediate-key memory means for updating the intermediate-key using the intermediate-key update-information;
• wherein said recording medium has a recorded program to operate said encryption apparatus such that at least one of said conversion means coupled with said intermediate-key memory means, at least one of said coupled conversion means is subjected to control of an intermediate-key stored in said intermediate-key memory means and generates a parcel of the intermediate-key update-information for updating the intermediate-key whenever the bit string conversion is performed, and transmits said intermediate-key update-information to said intermediate-key memory means forming a pair with said conversion means;
• said intermediate-key memory means further comprises an initial value memory for storing a predetermined number of the initial-values which are delivered from said intermediate-key generating means;
• and said apparatus further comprises a selecting means for selecting at least one initial-value among the initial-values stored in said intermediate-key memory means whenever the bit string conversion is performed, controlling the conversion means in a pair and updating the intermediate-key based on said intermediate-key update-information.