Modifying Playfair Cipher Algorithm by using Legendre Symbol

Abstract

In recent years, transmitting data on the Internet became a daily usage of people, such as sending emails, online shopping and so on. Generally, this data should be confidential and hence it should be secured by using cryptosystem algorithms. A new algorithm of securing the transmitted data by combining Playfair Cipher with Legendre symbol is presented in this paper. In this algorithm a large prime number can be chosen by both of sender and the receiver in order to calculate Legendre Symbol and then sorting them in a random order set. Moreover, as Legendre symbol is either 1 or -1, then this helps them in the proposed algorithm to use two tables with two keywords for the encryption and decryption processes instead of using only one table and one keyword as in the standard Playfair cipher algorithm. Thus, our proposed algorithm increases the security level of the transmitted data on the insecure channels comparing with the standard algorithm.