Patent ID: 8054967

Claim:
A computer system for encrypting a plain text and decrypting a ciphertext by performing a conversion process for converting partial data related to at least one of the plain text and the ciphertext into converted data which corresponds to the partial data, the computer system comprising: a main memory unit storing a conversion table and a computer program, the conversion table including at least one piece of inclusion data of a predetermined length and including a single piece of valid converted data at a predetermined position in the inclusion data, such that all other positions in the inclusion data store data irrelevant to the conversion process, and the computer program including a plurality of instructions for obtaining the converted data in the conversion process by using the conversion table; a cache memory unit including a cache line unit of the predetermined length; and an execution unit operable to fetch each instruction of the plurality of instructions from the computer program, decode each fetched instruction, and operate according to a result of the decoding of each fetched instruction, wherein, in order to obtain the converted data included in the conversion table, the execution unit (i) first attempts to obtain the converted data from the cache line unit, (ii) obtains the converted data from the conversion table stored in the main memory unit when the converted data is not present in the cache line unit, and (iii) writes the inclusion data including the obtained converted data to the cache line unit, and wherein the computer program includes: an obtaining instruction for obtaining the partial data; an operation instruction for calculating the predetermined position of the obtained converted data using the obtained partial data; and a reading instruction for reading the converted data located at the calculated predetermined position.