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Article

О ГРАНИЦАХ ЗАШУМЛЕНИЯ ТЕКСТОВ ПРИ СОХРАНЕНИИ ИХ СОДЕРЖАНИЯ. ПРИЛОЖЕНИЯ К КРИПТОГРАФИИ

Бабаш А. В., Баранова Е. К., Лютина А., Мурзакова А., Мурзакова Е., Рябова Д., Семис-оол Е.

Purpose: to introduce mathematical model of a distorted meaningful text and a measure of its distortion, to define a numerical classification of the distortion of meaningful texts, present applications of the model in cryptography.

Research methods: a more complex Vigenere cipher decryption that uses an almost periodic key (noisy) is performed as decryption of noisy plaintext on a periodical key (by well-known Vigenere decryption methods), but with a different probability distribution of plaintext characters, with further lead of the task to the acceptable noise level in plaintext determining for understanding this text content.

Results: gamming cipher decryption ways with weak keys are presented. A new complexity was obtained and the reliability of the method was improved due to the fact that there k-noisy weak (almost periodic) keys are more than periodic ones. The formula for calculating the probability of occurrence of characters after the k-th noise was obtained. Artificial languages for ease of calculation were introduced and practical examples of text noise (the necessary  calculations were made using a written program in the python programming language) were considered. The quality of the distorted plaintext content was assessed by highlighting of two borders of understanding.