Hitachi, Ltd.

Yutaka Otsu

Hiroshi Yoshiura

Kazuo Takaragi

Yusuke Hino

Yasuhiro Takahashi

Susumu Matsui

Yukio Nakata

Seiichi Domyo

Takeshi Kondou

Yoshiaki Hattori

Hiromasa Murakami

An information processing system including a data input means ( ) for inputting or receiving data, a data compressing means ( ) for compressing the data, a decompressing means ( ) for decompressing the compressed data and a main storage ( ) is provided with an encrypting means ( ) for encrypting the data and a decrypting means (220) for decrypting the encrypted data. In execution of a compression/encryption step in which the compressing means ( ) and the encrypting means ( ) perform compression and encryption for a part of the data and a decryption/decompression step in which the decompressing means ( ) and the decrypting means ( ) perform decompression and decryption for a part of the compressed and encrypted data, amounts of series of data processed in the compression/encryption and decryption/decompression steps are so set that a memory capacity required for executing the processings does not exceed capacity of the main storage, wherein the compression/encryption and decryption/decompression steps are repeated more than once inclusive.

Data decompression/decryption method and system

Data compression/encryption method and system

In a data compression method using dictionaries, there are adopted a dynamic dictionary and a static dictionary to prevent the deterioration in the data compression ratio in the leading portion of the input data which cannot be efficiently compressed using the dynamic dictionary. Moreover, the configuration removes the disadvantage of the deterioration in the data compression ratio because character strings having a low appearance frequency occupy a large portion of the dictionary. Data to be compressed is inputted via an input unit to be decomposed into input bit strings 202. Using the input bit string as a retrieval key, a bit string retrieval is conducted through the static dictionary by a decision unit and a reference unit. According to a result from comparison between the input bit string and a bit string of the static dictionary and a result from the retrieval by a retrieving unit through the dynamic dictionary, whether or not the input bit string is to be registered to the dynamic dictionary is determined. For registration of the input bit string, an index is added thereto by a register unit before the registration. The input bit string or an index matching the string is outputted as compressed data.

Method of and apparatus for compressing and decompressing data and data

Data is compressed/encrypted for communication between application programs without addition of any modification to the application programs. In a communication system where a plurality of personal computers are connected to each other using communication lines, a personal computer is provided with a communication program and an application program, the application program uses a command offered by the communication program for transmission and reception of data with another personal computer, a hooking program for discriminating the command related to the data communication issued by the application program is provided and, after the hooking program has compressed or encrypted the data of application program depending on a type of the command, the command is transferred to the communication program.

Communication system

Growing community of inventors

Hadano, Japan

Yutaka Otsu