Enhancing the Security of Playfair Square Cipher by Double Substitution and Transposition Techniques

Cryptography is an art and science of converting original message into no readable form. There are two techniques for converting data into no readable form. Transposition technique, Substitution technique. In recent years there is drastic progress in Internet world. Sensitive information can be shared through internet but this information sharing is susceptible to certain attacks. Cryptography was introduced to solve this problem. Cryptography is art for achieving security by encoding the plain text message to cipher text. Substitution and transposition are techniques for encoding. When Caesar cipher substitution, Rail fence cipher and Columnar Transposition Cipher techniques are used individually, cipher text obtained is easy to crack. This Paper will present a perspective on combination of techniques like substitution and transposition with playfair square cipher to enhance its security. Playfaircipher is one of the popular symmetric encryption methods. The first recorded description of the Playfaircipher was in a document signed by Wheatstone on 26 March 1854. However Lord Playfair promoted the use of this cipher and hence it is called Playfair Cipher. It was used by the British in the Second Boer War and in World War I. It was also used by the Australians and Germans during World War II. Playfair is reasonably easy to use and was used to handle important but non-critical secrets. By the time the enemy cryptanalysts could break the message, the information would be useless to them. Between February 1941 and September 1945 the Government of New Zealand used it for communication between New Zealand, the Chatham Islands and the Pacific Islands. To enhance its security we combine it with transposition and substitution cipher techniques, to minimize attacks on it (Cryptanalyst), by performing double substitution and transposition Techniques.