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.
