New Polyalphabetic Substitution Scheme for Secure Communication
Ranju S. Kartha1, Varghese Paul2

1Ranju S. Kartha*, School of Computer Science, Mahatma Gandhi University, Kottayam, India.
2Dr. Varghese Paul, Department of CSE, RSET, Cochin, India.
Manuscript received on December 14, 2019. | Revised Manuscript received on December 24, 2019. | Manuscript published on January 10, 2020. | PP: 3303-3310 | Volume-9 Issue-3, January 2020. | Retrieval Number: C9043019320/2020©BEIESP | DOI: 10.35940/ijitee.C9043.019320
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Abstract: The internet is a very powerful and useful tool for communication, information and connectivity. So it is very important to keep yourself safe and secure online. The best way of secure information is encryption; there are many cryptographic algorithms available for encryption. These cryptographic algorithms are classified according to their encrypting process; as substitution cipher or transposition cipher. In Polyalphabetic ciphers, the substitution rule changes continuously from character to character according to the keyword and plaintext. Vigenere cipher is considered to be the most efficient Polyalphabetic substitution cipher. But it is vulnerable to attacks, due to its repeating nature of the keyword. To overcome this vulnerability, here we are presenting a new Polyalphabetic substitution scheme which uses infinite number of 26 x 26 random tables for encryption. During encryption, whenever the keyword repeats, this proposed Polyalphabetic substitution cipher generates a 26 x 26 alphabetical random table. Instead of using the same Vigenere Table here we are using an infinite number of alphabetical tables depending on the length of the plaintext and keyword. Each random table will be completely independent from the previous table. This will reduces the repeating sequences in the ciphertext. The repeating nature of the keyword does not help the crackers to break this code. So this proposed Polyalphabetic substitution cipher is considered as an unbreakable cryptosystem. The Proposed Polyalphabetic cipher can provide security for many applications such as web transactions, web transactions, personal emails, secret information transmitted between public or private organization, military application etc. 
Keywords: Polyalphabetic Cipher, Vigenere Cipher, Vigenere Table, Kasiski Method, Index of Coincidence IC.
Scope of the Article:  Communication