ABSTRACT
Cryptography is the science of converting any secret information into indecipherable text to make it secure and immune to attacks. It consists of various techniques that allow only the sender and the receiver to understand the information meaningfully. The Wheatstone Playfair Square is a symmetric substitution encryption technique that is traditionally weak and easy to break. The main motive of this chapter is to make the traditional Playfair cipher more secure and attack-proof by securing the keyword of the Playfair cipher using the Diffie–Hellman algorithm and by changing the techniques of the Playfair cipher to an extended/improved version. The chapter introduces a new and extended version of the Playfair cipher, which has the role of a private key in encryption and decryption. The chapter has proposed a new algorithm using fuzzy logic with the aim to make communication more secure. The process will have two stages, wherein the first stage, the Diffie–Hellman algorithm will be used to exchange the secret key between the sender and the receiver. Furthermore, the secret key exchanged by the Diffie–Hellman algorithm will be used to find the private key for the extended Playfair cipher. In the second stage, the traditional Playfair cipher technique will be modified 122by changing the way of doing encryption and decryption, as now the secret key will determine the movement of alphabets in the Playfair square. Finally, the advantages of this new combination will be analyzed.
