Security Enhancement of Play fair Cipher Using Modified BBS and Keystream Values

Abstract

Today, information’s are shared and stored on the cloud. Thus, security concerns with this information are a big concern, and as technology advances, hackers can use these cutting- edge technologies to attack the data. In order to protect this data, it is required to use a security mechanism called cryptography. Cryptography is the process of changing intelli- gible data to unintelligible data using key and encryption algorithms. There are two types of cryptography namely symmetric and asymmetric. Playfair cipher is a symmetric cipher that encrypts a pair of letters at the same time. The goal of this study is to improve the secu- rity of the Playfair cipher by using a modified Blum Blum Shub algorithm and Keystream values. The Blum Blum Shub algorithm is altered using four blum prime numbers and used to generate random number and then, it will be a key after finding the equivalent character of the generated random number sequences. In this study, we securely swapped the key and resolve the need for filler characters when related characters are combined to make a bigram. Furthermore, we have also hide the relationship between plaintext and cipher text bigrams by modifying the encryption mechanism of playfair cipher. Further, here, reciever did not recieve the key directly instead it can generate the same key with that of the sender and this overcomes the key exchange problem of playfair cipher. Finally, the proposed algorithm has been evaluated through computer simulations namely Matlab soft- ware. In order to evaluate the performance of the proposed work, we have used Avalanche effect, confusion and diffusion , frequency analaysis and brute force attack as an evalua- tion parameter. Finally, the simulation result shown that the proposed algorithm provides a high avalanche effect ratio , generate a complex key which is difficult to predict and it require a lot of time to be cracked by cryptanalaysis attack. A single character change in the plaintext provide an average of 98.572% of avalanche result. So, the proposed work is secured than the extended algorithm.