EXPANDING KEY GENERATOR, ENCODING/DECODING APPARATUS, EXPANDING KEY GENERATING METHOD, AND MEMORIZING MEDIUM

摘要

PURPOSE: An expanding key generator, an encoding/decoding apparatus, an expanding key generating method, and a memorizing medium are provided to prevent the generation of a weak key, improve the randomness of an expanding key, and improve encoding strength. CONSTITUTION: An expanding key generator(10) generates n-steps expanding keys(K1-Kn) from a common key. A data randomizing unit(20) successively encodes or decodes the expanding keys(K1-Kn) generated by the expanding key generator(10) using each round(R1-Rn). The expanding key generator(10) corresponds to each round(R1-Rn), and key conversion functions(fk1-fkn) are installed in the expanding key generator(10). If the common key or intermediate key conversion functions(kc1-kcn-1) are inputted, the key conversion functions(fk1-fkn) output the expanding keys(K1-Kn1) to round functions(fr1-frn) of the data randomizing unit(20) and input the intermediate key conversion functions(kc1-kcn-1) to next step key conversion functions(fk2-fkn).