Playfair is one of the best-known traditional ciphers but it is limited to different aspects such as: white space, numbers and other printable characters. The existing technique is based on the use of a 5 × 5 matrix. This algorithm can only allow the text that contains uppercase alphabets only. But many algorithms have been proposed which allow extension of playfair to: 6 × 6 matrix, 8 × 8 matrix and 7 × 4 matrix. This dissertation deals with some of the limitations such as lowercase, numbers, white space and repetition of alphabet in pairs. Proposed modification uses rhotrix which is a new paradigm of matrix theory for rectangular arrays. This work proposes an improved key matrix formation of the playfair cipher. The order of the rhotrix will be set to 6 to make it compatible with the [n×(n-1)] mode of rhotrix representation which supports all 26 alphabets in both upper case letters (A-Z) as well as lower case letters (a-z), ten digits (0-9), special characters and the extended special characters. Experimental result produced better playfair cipher to incorporate randomness and to eliminate the chances of being attacked by frequency testing of character occurrence over an existing 11 × 11 matrix. The system was developed in java because of platform independence and availability.
DEVELOPMENT OF AN IMPROVED PLAYFAIR CRYPTOSYSTEM USING RHOTRIX