International Journal of Computer Applications (0975 – 8887) Volume 103 – No 13, October 2014 16 Enhanced the Security of Playfair Technique using Excess 3 Code (XS3) and Ceasar Cipher Zubair Iqbal Asst. Prof., Dept. of CS & IT, M.I.T, Moradabad Bhumika Gupta Asst. Prof., Dept. of CS&E, GB Pant Eng. College Kamal Kr. Gola Lecturer in Dept. of CS&E. T.M.U., Moradabad Prachi Gupta Asst. Prof., Dept. of CS & IT, M.I.T, Moradabad ABSTRACT The main purpose of our research is to provide security for the data that contains alphabets and integer values during the transmission, when data is transmitted form sender to receiver. As we know that playfair technique if best for multiple letter encryption, which treats the plain text as single units and translates these units into cipher text. It is highly difficult to the attacker to understand or to decrypt the cipher text. The existing playfair technique is based on the use of a 5 X 5 matrix of letters constructed using a keyword. This algorithm can only allow the text that contains alphabets only. But many algorithms have been proposed that allow text which contains alphabets, integers as well as special symbols using 6 * 6 matrix and 10 * 9 matrix etc. In playfair technique a groups of 2 letters in the plain text is converted to cipher text during encryption using a key. Similarly on other hand during decryption cipher text are converted to plain text using the same key. Some time it may be possible for the attacker to understand the plaintext. To overcome this problem we proposed an algorithm that extends the security of playfair technique using excess 3 code and ceasar cipher technique where first each alphabets and integer is converted into binary number and then its equivalent excess 3 code and after that with the help of key encryption process will be apply. In our proposed technique we are using 6 * 6 matrix which contain alphabets and integers only. General Terms SECURITY Keywords Playfair cipher, excess 3 code, ceasar cipher, Plaintext, cipher text, rectangular matrix, key, encryption, decryption, binary number. 1. INTRODUCTION The Playfair cipher or Playfair square is a manual symmetric encryption technique and was the first literal digraph substitution cipher. The scheme was invented in 1854 by Charles Wheatstone, but bears the name of Lord Playfair who promoted the use of the cipher. When information is transmitted from the sender to the receiver care should be taken so that the information is not accessible to a third party. One of the ways to protect information is the method of encryption and decryption whereby the sender encrypts the message with a secret key which is known only to the receiver. Once the receiver gets the message the message is decrypted using the same secret key. This type of encryption is known as symmetric encryption. Playfair cipher[1] is one of the well known symmetric encryption methods. The first recorded description of the Playfair cipher [2] 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. The technique encrypts [3] pairs of letters (digraphs), instead of single letters as in the simple substitution cipher. The Play fair cipher uses a 5 by 5 table containing a key word or phrase. Memorization of the keyword and 4 simple rules was all that was required to create the 5 by 5 table and use the cipher. 2. TRADITIONAL PLAYFAIR CHIPER TECHNIQUE This section briefly described the existing play fair cipher algorithm. The existing play fair cipher algorithm is based on with use of 5 X 5 matrix of letters constructed using a keyword. The existing Playfair algorithm is based on the use of a 5 X 5 matrix of letters constructed using a keyword. The 5 X 5 matrix can only allow 25 characters, hence the letters I/J count as one. If we encrypt the plain text which is having the letter I/J and when we decrypt the ciphertext at the receive end, the receiver will be under ambiguity whether to consider I or J in his text, because the meaning can be changed with the change of the letters. This algorithm can only useful for the plain text containing of alphabets but it is failed for the plain text containing of alphanumeric values. That means the plain text that is to be encrypted can only have alphabets but should not contain digits or numbers. For example: