IT-100

The model of a cryptosystem with the best speed and selectable security.

WeaCheslaw Oleinik

Dekart, 1, Ghioceilor str., Kishinev MD-2008, Republic of Moldova Tel. +(3732) 245580, fax. +(3732) 242580, E-mail: owl@dekart.com

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Key words: information security, cryptography, cipher, model. In many if not in all practical applications using symmetric cryptography systems, the main requirement is reaching the greatest possible speed of encoding. Thus the system should provide a necessary level of cryptography security. These two requirements are as a matter of fact contradictory, i.e. rise of speed of the system results in its lowering cryptographic security and on the contrary. Therefore at creation of cryptosystems very important there is a correct choice of a relation between speed of encoding and cryptographic security of systems. In the paper it is shown, that cryptosystems on the basis of ciphers such as Vernam cipher [1] together with customized generators of keys provide possibility of the balanced choice between cryptographic security of the created cipher and its speed. It is possible due to that Vernam cipher has (as has shown C. Shannon [2]) one prominent feature, consisting that it is theoretically proof cryptography system. As Vernam cipher uses only one operation its speed will be greatest possible and constant for concrete implementation for encoding. For obtaining a key with long equal to length of the message some ideal generator of a pseudo-random sequence is used. The ideal generator is understood as the generator producing an infinite, not repeating, random sequence which complexity of a prediction depends only on length of "priming", i.e. from first time load of the generator. Application of the similar generator of a key sequence for Vernam cipher results to that cryptography security of the system the whole becomes dependent only from are long first time load of the generator. The Ideal generators exist, but, unfortunately, they are difficultly sold in practice. However for these purposes it is possible to use the generators constructed on a basis so-called of hashing functions. One of properties such functions are that they provide impossibility of a prediction of an entry sequence at known output values and the algorithm of conversion. The truth maximum length of a sequence received with the help of such generators will not be infinite, but it usually enough big, that is acceptable to practical application. References [1] G. S. Vernam, “Cipher printing telegraph systems for secret wire and radio

telegraphic communications,” J. Atner. Inst. Elec. Eng., vol. 55, pp. 109-115, 1926.

[2] C. E. Shannon, “Communication theory of secrecy systems”, Bell System Technical Journal, 28 (1949), 656-715.

WeaCheslaw Oleinik, Dr. of C.S., Ass. Academician of IIA, born: July 4, 1956. Author: over 60 papers.