Cryptology ePrint Archive: Report 2008/397

A Framework for the Development Playfair Cipher Considering Probability of Occurrence of Characters in English Literature

Uttam Kr. Mondal , Satyendra Nath Mandal and J. PalChoudhury

Abstract: The Playfair cipher was the first practical digraph substitution cipher. The scheme was invented in 1854 by Charless Wheatstone, but was the named after Lord Playfair who promoted the use of the cipher. In this paper, two algorithms have been proposed to written the Playfair cipher. The first effort is being made to write the playfair cipher in a new way by considering the probability of the occurrence of english character in context to english literature. In the proposed algorithm at each and every time, the algorithm will check whether, the plain text contains odd number of words or not. If the plain text is of odd number of characters, the algorithm will concatenate a dummy character at the end with lowest probability to form even length word in the cipher text and then search is being made in the dictionary to find out whether the word with dummy character is present in the dictionary or not. If that word is present in the dictionary, delete that dummy character of that word and the same effort is being made with another dummy character with next lowest probability occurrence. The second method add another new approach, it replace all blanks between two consecutive word by some character which has least probability to appear at that position in the sentence and search the dictionary to check whether this new word has different meaning . If new word if present, replace blank with next higher probability character for this blank. Finally, time comparison has made of encryption and decryption of some sentences using original with two algorithms and it has been found that the decryption time are much better than original play fair algorithm and that will produce the original message from encrypted message directly.

Category / Keywords: secret-key cryptography /

Date: received 18 Sep 2008, withdrawn 27 Nov 2008

Contact author: satyen_kgec at rediffmail com

Available format(s): (-- withdrawn --)

Version: 20081127:083026 (All versions of this report)

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