MS EXCEL-BASED APPLICATION FOR ENCRYPTION AND DECRYPTION USING THE HILL CIPHER ON THE BASIS OF 2X2-MATRIX AND 64-SYMBOL ALPHABET
MS EXCEL-BASED APPLICATION FOR ENCRYPTION AND DECRYPTION USING THE HILL CIPHER ON THE BASIS OF 2X2-MATRIX AND 64-SYMBOL ALPHABET

Summary/Abstract: In classical cryptography, the Hill cipher, invented by Lester Hill in 1929, was the first polygraphic substitution cipher based on linear algebra, which practically processed more than three symbols at once. In the classical Hill cipher, each letter is represented by a number modulo 26. To encrypt a message, each block of n letters (considered as an n-component vector) is multiplied by an invertible matrix of size n×n, again modulus 26. In order to decrypt the message, each block is multiplied by the inverse matrix of the matrix used for encryption. In the paper a modified algorithm for encryption and decryption using the Hill cipher on the basis of 2×2-matrix and 64-symbol alphabet is proposed. Here each symbol (Latin letters, decimal digits and punctuation signs) is represented by a number modulo 64 and all arithmetic operations are done by modulo 64 (the number of letters in the alphabet instead of modulo 26). The paper describes MS EXCEL-based application implementing the processes of encryption and decryption of English texts using the Hill cipher based on the matrix of size 2×2 and 64-symbol alphabet. The processes of encryption and decryption of 6-character words in English are illustrated. Numerous examples obtained by the application developed are presented in the paper. The material is used in the educational process in the course “Telecommunication Security” by students of the specialty “Telecommunication Systems” for the Bachelor degree at the University of Ruse but it can be applied in other disciplines involving issues of cryptographic information protection.

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