Cryptography – Communication system using cryptography – Having compression
Reexamination Certificate
2000-08-25
2002-06-25
Hayes, Gail (Department: 2132)
Cryptography
Communication system using cryptography
Having compression
C037S217000, C708S203000, C708S204000
Reexamination Certificate
active
06411714
ABSTRACT:
TECHNICAL FIELD
The present invention relates to compression and encryption of data and more particularly to a data compression/encryption method and a system therefor which are designed to enhance the processing efficiency while reducing power consumption in performing compression processing as well as encryption processing on data.
BACKGROUND ART
In accompanying with rapid increase in utilization of communication facilities, there arises an increasing trend of compressing and encrypting (hereinafter referred to as compression/encryption or compressing/encrypting for short) the data with a view to enhancing the efficiency of communications and preventing unauthorized acquisition and falsification of the data for communication. In particular, in the case of wireless communications, since interception is easy because of narrow band, the compression/encryption is indispensable. On the other hand, in the portable type computers commanding high popularity in recent years, duration of a battery provides an important problem, giving rise to a demand for the data processing methods suited for economization of electric energy. For these reasons, the compression/encryption techniques which can ensuring high efficiency and low power consumption are demanded as being indispensable.
In the conventional compression/encryption techniques known heretofore, data is compressed at first and then written into a secondary storage such as a hard disk drive or the like, whereon the compressed data is read out from the secondary storage to be encrypted. In the encryption processing, same encryption processing as that for the non-compressed data is adopted without taking into consideration the fact that the data are compressed. Further, in the processing for restoring the original data from the compressed/encrypted data (this process will hereinafter be referred to as the decryption/decompression processing), the data is decrypted at first and then written in the secondary storage, whereon the decrypted data is read out from the secondary storage to be restored or decompressed.
In the conventional compression/encryption technique described above, the compression processing and the encryption processing are executed independent of each other without exploiting the possibility that the processing efficiency can be enhanced by integrating or combining together the compression processing and the encryption processing. Besides, because the compression processing and the encryption processing on one hand and the decryption processing and the decompression processing on the other hand are interlocked by way of the secondary storage, not only a time is taken for reading/writing data in/from the secondary storage but also large amount of electric energy is consumed for the read/write operation.
An object of the present invention is to provide a data compression/encryption method and a system therefor which are capable of enhancing the efficiency of processings involved in the compression/encryption as well as the decryption/decompression while reducing the power consumption by combining together the compression processing and the encryption processing for thereby rendering unnecessary to interlock the compression processing and the decompression processing on one hand and the decryption processing and the decompression processing on the other hand by way of the secondary storage.
DISCLOSURE OF INVENTION
In order to make unnecessary the interlock between the compression processing and the encryption processing on one hand and between the decryption processing and the decompression processing on the other hand by way of the secondary storage, an amount of data processed at a time is so limited that a memory capacity required for performing the compression/encryption processings and the decryption/decompression processings does not exceed the capacity of a main storage of a relevant information processing system. In other words, the amount of the data processed at a time is partitioned such that a memory capacity required for performing the compression/encryption processings and the decryption/decompression processings does not exceed the capacity of the main storage of the relevant information processing system, and then, the data compression/encryption processings are executed sequentially and repetitively on a partitioned-data basis to thereby compress and encrypt one set of data wholly.
More specifically, according to a first method of the present invention, an encrypting means and a decrypting means are provided in an information processing system which includes a compressing means and a decompressing means for the data, wherein the amount of data to be compressed and encrypted or the amount of data to be decrypted and decompressed is so set that the memory capacity required upon application of the compressing means and the encrypting means to the data as well as the memory capacity required upon application of a decrypting means and the decompressing means to the data does not exceed the capacity of the main storage incorporated in the relevant information processing system, and the application of the compressing means and the encrypting means or the application of the decrypting means and the decompressing means to the data of the amount as set is repeated to thereby compress and encrypt or decrypt and decompress the whole data.
Next, description will be directed to the enhancement of the processing efficiency owing to the combination of the compression processing and the encryption processing. As is described in “DATA COMPRESSION HANDBOOK” published by TOPPAN-PUB. (1994), pp. 21-247, there are known undermentioned methods (1) to (3) as the conventional compressing methods. In practical data compression programs, combination of the methods (1) and (3) or alternatively combination of the methods (2) and (3) is adopted in many cases.
(1) Method based on a fixed statistical model such as e.g. fixed Huffman coding.
(2) Method based on an adaptive statistical model such as e.g. adaptive Huffman coding.
(3) Dictionary base method such as e.g. LZ77 and LZ78.
The compression/encryption method according to the present invention is applicable to the above-mentioned methods (1) and (2). Furthermore, although the present invention can not find application straight-forwardly to the method (3), the invention is applicable to the combination of the methods (1) and (3) or the combination of the methods (2) and (3).
In the first place, description will be made of incorporation of the encryption processing in the compression processing based on the fixed statistical model. According to the compression method based on the fixed statistical model, occurrence probabilities of individual symbols are determined by resorting to a method of checking the frequencies at which the individual symbols make appearance in the data. On the basis of the occurrence probability of the symbol, correspondence information between the symbol and a bit string corresponding thereto (Huffman tree in the case of Huffman coding) is generated. In that case, the symbol making appearance at higher probability is assigned with a shorter bit string upon establishing the correspondence between them. Subsequently, the symbols contained in the data are translated into corresponding bit strings for thereby compressing the data. In the decryption processing, the compressed data and the symbol-bit string correspondence information (or occurrence frequencies or occurrence probabilities of the symbols for generating the symbol-bit string correspondence information) are received to restore the original data through reverse translation of the bit strings into the symbols, respectively.
In the compression method based on the fixed statistical model as mentioned above, the data restoration is impossible unless the symbol-bit string correspondence information can not be made use of. In this conjunction, it is h however noted that by encrypting only the symbol-bit string correspondence information, the intrinsic aim of the encryption can be achieved. Because the amou
Hino Yusuke
Otsu Yutaka
Takaragi Kazuo
Yoshiura Hiroshi
Antonelli Terry Stout & Kraus LLP
Darrow Justin T.
Hayes Gail
Hitachi , Ltd.
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