Cryptography – Particular algorithmic function encoding
Reexamination Certificate
1999-01-26
2003-01-07
Barrón, Gilberto (Department: 2132)
Cryptography
Particular algorithmic function encoding
C380S001000, C380S002000
Reexamination Certificate
active
06504929
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an encryption strength evaluation support apparatus suited to evaluating the encryption strength of encryption device by using a statistical method and a mechanically readable recording medium recording an encryption strength evaluation support program.
2. Description of the Prior Art
Conventional techniques of evaluating the strength of encryption algorithm are roughly classified into those based on a specific decoding method and those based on statistical methods.
Examples of the encryption strength evaluation based on a specific decoding method are “Method and Apparatus for Evaluating Strength of Encryption Algorithm” described in Japanese Unexamined Patent Publication No. 8-190344 and “Encryption Performance Evaluation Apparatus” described in Japanese Unexamined Patent Publication No. 9-160489 similar to the former patent. Either technique evaluates the strength of encryption algorithm in terms of strength against linear decoding for block encryption. That is, the former technique finds a linear approximate expression having a maximum deviation ratio obtainable from an encryption algorithm whose strength is to be evaluated. On the basis of the result of this search, the strength of encryption algorithm against linear decoding is evaluated. The latter technique attempts to improve the performance of evaluation by increasing linear correlation detection efficiency in linear decoding. Details of the linear decoding are described in Mitsuru Matsui (“DES Encryption Linear Decoding method (1)”, SCIS93-3C (January, 1993).
On the other hand, the conventional encryption strength evaluation based on statistical methods is described in, e.g., “Encryption and Information; Security” (Mar. 29, 1990, Shokodo), “2.5 Ciphertext Randomness Evaluation Indices” (pp. 49-56). That is, this technique evaluates the encryption strength by using numerical values such as the maximum value, mean value, and variance of the correlation between input land output data. This reference also describes discrimination between the strengths of a plurality of encryption algorithms by comparing these numerical values.
The encryption strength evaluation based on a specific decoding method depends upon the specific decoding method called linear decoding. Therefore, this technique cannot evaluate in principle the strength of encryption algorithm to which this decoding method is not applicable, and hence lacks versatility. In contrast, the method of evaluating encryption strength by using a statistical method is highly versatile because the method does not depend upon any specific decoding method.
Unfortunately, the conventional encryption strength evaluation technique based on a statistical method evaluates encryption strength by using numerical values such as the maximum value, mean value, and variance of the correlation between input and output data. Since these values are representative values of a large number of sample values, this technique cannot finely analyze the behavior of encryption conversion. In some instances, evaluation errors may take place.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation and has as its object to provide an encryption strength evaluation support apparatus capable of evaluating encryption strength independent of any specific decoding method and finely analyzing the behavior of encryption conversion, and a mechanically readable recording medium recording an encryption strength evaluation support program.
It is another object of the present invention to provide an encryption strength evaluation support apparatus capable of easily analyzing the behavior of encryption conversion, and a mechanically readable recording medium recording an encryption strength evaluation support program.
To achieve the above objects, according to the first aspect of the present invention, there is provided an encryption strength evaluation support apparatus comprising statistical data sampling program executing means for statistically obtaining correlations between individual bits of input and output data of an encryption device to be evaluated, statistical result storage means for storing the bit correlations obtained by the statistical data sampling program executing means, and statistical result edit/output means for editing and outputting the bit correlations stored in the statistical result storage means in the form of a table or a two- or three-dimensional graph.
In this encryption strength evaluation support apparatus, the statistical data sampling program executing means statistically obtains correlations between individual bits of input and output data of an encryption device to be evaluated and stores the bit correlations in the statistical result storage means. The statistical result edit/output means edits and outputs the bit correlations stored in the statistical result storage means in the form of a table of a two- or three-dimensional graph. Accordingly, it is possible to evaluate encryption strength independently of any specific decoding method and finely and easily analyze the behavior of encryption conversion.
According to the present invention, there is provided an encryption strength evaluation support apparatus further comprising, in addition to the arrangement of the first aspect, evaluation object program forming means for forming an encryption program to be evaluated, wherein the statistical data sampling program executing means statistically obtains correlations between individual bits of input and output data of the evaluation object program formed by the evaluation object program forming means. This allows a single apparatus to design and evaluate an encryption algorithm and thereby improves the efficiency of development.
According to the present invention, there is provided an encryption strength evaluation support apparatus further comprising statistical program library means for holding, for each predetermined evaluation item, a statistical program for calculating data necessary to evaluate the evaluation item, and evaluation object data group generating means having evaluation object program forming means for forming an encryption program to be evaluated, evaluation condition setting means for setting evaluation conditions, and interface function setting means for setting an interface between the evaluation object program formed by the evaluation object program forming means and the statistical programs, the evaluation object data group generating means holding an evaluation object data group including the formed evaluation object program and the set evaluation conditions and interface, wherein the statistical data sampling program executing means comprises statistical data sampling program generating/activating (restarting) means for generating a statistical data sampling program for statistically obtaining correlations between individual bits of input and output data of the evaluation object program from the evaluation object data group and the statistical programs in the statistical program library means. This allows a single apparatus to design an encryption algorithm and evaluate the algorithm by using the statistical programs previously held in the statistical program library means, thereby improving the efficiency of developmental
According to the present invention, the statistical program library means comprises a basic function library of basic functions such as addition, subtraction, and logical operations, and statistical program library generating means for generating a statistical program to be added to a statistical program library by using the basic functions of the basic function library. This allows the user to freely form any statistical program and perform evaluation by using the program.
According to the present invention, the statistical data sampling program executing means comprises means for sequentially collecting statistical data for a plurality of evaluation items. Consequently, a plurality of evaluation items c
Barrón Gilberto
Zand Kambiz
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