Cryptography – Particular algorithmic function encoding
Reexamination Certificate
1999-03-17
2001-10-09
Decady, Albert (Department: 2132)
Cryptography
Particular algorithmic function encoding
C380S042000, C380S043000, C380S044000, C380S046000, C380S047000
Reexamination Certificate
active
06301361
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to encryption, and more particularly to protecting information from unauthorized access, and may be used in crypt-systems for encoding, transferring or storing, and decoding of communications or data as well as in others systems for protecting information.
DESCRIPTION OF THE RELEVANT ART
The prior art describes technical solutions which provide protection of transferred information by using a special device or encoding software. Victor Garish “Practical Guide on Protecting Commercial Secrets”. Simferopol, TAVRIDA, 1994, p.35-37, FIG. 22, describes a scrambler for protecting telephone conversations. The scrambler operates on the principal of inverting an audio signal. Ordinary speech is changed into a nonsensical set of sounds, but the initial signal is received without any distortion. The scrambler includes a coder for changing voice. The coder is filled with 13,122 user's codes, which provide 52,488 digital combinations. The scrambler has resident software, which encodes and decodes the transferred information in several variants and controls the operation of the scrambler as a whole. This prior art solution, however, has a problem in providing a fair degree of secrecy since for decoding the secret codes, one only needs to perform a limited number of mathematical operations. The mathematical operations may be performed quickly and effectively by modern, high-speed computers and/or devices.
A main characteristics of a crypt-system is the degree of secrecy. The task of a cryptographer is to provide the utmost secrecy and authenticity of the transferred information. Alternatively, a crypt-analyst “forces open”, or “breaks”, the crypt-system designed by a cryptographer. The crypt-analyst tries to decipher the set of encoded symbols and to deliver the encrypted communication as the plaintext.
Prior art discloses technical solutions for protecting the transferred information by using a specific device and/or encoding software. Known codes are based on two simple methods. substitution and interchange. Interchange uses simple mixing of plain-text symbols. The key of an interchange encryptor defines the specific type of mixing. The frequency distribution of individual symbols in the encoded text is identical to that of the plaintext. For substitution, each symbol of the plaintext is replaced by another symbol of the same alphabet, and the specific type of substitution is determined by the secret key.
For example, the algorithm in the Data Encryption Standard (DES) uses substitution and interchange. Schmidt M. E., Bransted D. K. “Standard of Data Encoding: Past and Future” Journal of Works of Electronic and Radio Engineers (TIIER), 1988, v.76, no. 5., p. 33-34. The algorithm comprises plaintext, enciphered text and the key as binary sequences having the length 64, 64 and 56 bits, respectively. When DES is used in an electronic book or table mode, the 64-bit blocks of the plaintext are encoded independently by using one key.
The algorithm of DES includes 16 rounds or cycles, each of which has simple interchanges combined with substitution in four-bit groups. In each pass, 48 key bits are selected in a pseudo-random manner from the full 56-bit key.
DES does not provide a fair degree of secrecy with 2
64
keys, since substitution of all keys during a brute-force attack using modern computer techniques is performed in an acceptable time. Also, using the same plaintext and not varying the keys, produces the same encoded text. Analysis reveals the statistical regularity of the correlation between the plaintext and the encoded text, and may allow decoding the encoded text without using direct substitution of all the keys.
A crypt-system using public keys is described in Schmidt M. E., Bransted D. K. “Standard of Data Encoding: Past and Future” Journal of Works of Electronic and Radio Engineers (TIIER), 1988, v. 76, no. 5., p. 37-39. This system uses a one-way function—discrete logarithms raising to a power, modulus a prime number.
Hatching is disclosed in Information Technology, Crypt Graphical Protection of Information, Cash function. M.: Gosstandart of Russia, 1994, 34.11-94, p. 3-8. Hatching uses an optional set of data, a sequence of binary symbols, with a short, fixed length. In this system 64-bit subwords are encoded using keys of 256 bit length.
The drawbacks of these systems are small the key length, which may permit decoding during acceptable time, even at a slow decoding speed. These systems are practically stable systems.
Theoretically stable systems have perfect secrecy. Shannon C. E.. “Communication Theory in Secret Systems”. Shannon C. E. “Works on Information and Cybernetics Theory”. M.: IL, 1963, p. 333-402, “Theoretically Stable system,”, as cited in “An Introduction to Contemporary Cryptology”, Proceedings of the IEEE, v. 76. No. 5, May 1998. Theoretically stable systems means that the plaintext, and the encoded text or cryptogram, are statistically independent for all plaintext and cryptograms.
A prior art Vernan crypt-system is a theoretically stable crypt-system. Theoretically stable systems make certain demands on a key. For a system with closed keys the length of a key should be not less than the length of the plaintext. In the Vernan system the key length is equal to the length of the plaintext. This system was used in a code-notebook, similar to a one-time pad. Vernan. “Copher Printing Telegraph Systems for Secret Wire and Radio Telegraphic Communications,” J Amer. Inst. Elec. Eng., vol. 55, pp. 109-115, 1926., describes a key which can be used only for transfer of one encoded text. This is the main drawback of a codebook because the key should be changed and delivered transferee with every encoded text.
Crypt-systems using randomisers are disclosed in Schmidt M. E., Bransted D. K. “Standard of Data Encoding: Past and Future” Journal of Works of Electronic and Radio Engineers (TIIER), 1988, v. 76, no. 5., p. 26-27. A randomiser is a software or a hardware device, that encodes some symbols of plaintext with some random codes. Typically, the randomiser provides equal frequency of the plaintext alphabet. Symbol frequency equalization is required so that a crypt-analyst cannot organize decoding of a plaintext based on analysis of frequency characteristics of encoded text. For a random plaintext and a random selection of a code, a derandomiser should correctly determine the initial symbol without transfer of information from the randomiser location. In classical systems, this task is solved by substituting codes belonging to the randomised symbol. Randomisers, however, do not play a substantial role in crypt-protectability of an encoding system, as secret keys are the main means of protection.
Related prior art includes “The First Years of Cryptography with Public Keys”, Proceedings of IEEE, v. 76, no. 5, May 1988, which describes the CY 1024 processor chip, manufactured by Cylink Corporation in Sunnyvale, Calif. The description indicated that the CY 1024 processor chip implements the RSA cryptographic system.
SUMMARY OF THE INVENTION
A general object of the invention is an encryption system which cannot be deciphered by crypt-analysis using existing technology.
Another object of the invention is an encryption system capable of generating encrypted or encoded symbols, which cannot be crypt-analyzed to determine the original symbols of the set of initial symbols. The “set of initial symbols” refers to the message to be encoded.
An additional object of the invention is a method for encoding and transferring or storing of information, wherein a key for decoding a set of encoded symbols is provided to an addressee in advance. The key includes information on the regularities that establish correspondence between the values of the transferred set of encoded symbols and definite symbols of the set of initial symbols, and vise versa. The mentioned regularities are used to process the information transferred to the addressee, a communication comprising data obtained as a result of processing the information. The values of the
Mischenko Valentin Alexandrovich
Zakharau Uladzimir Uladzimirovich
Callahan Paul E.
Chartered David Newman
De'cady Albert
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