Some Results of Data Encryption and Decryption using Euler’s Totient Function

In this paper, we discuss about the Hill Cipher cryptosystem, the RSA public-key cryptosystem, developed by Rivest, Shamir, Adleman for text encoding and decoding. To encrypt and decrypt the message, we use the Euler Phi-function, congruences, and matrix multiplication. Further, we employ two keys for coding and decoding. Introduction: In present, computer networks, internet and mobile communications are important and inevitable part of our society and security of information from hackers is a big task. One of the most widely used applications for information security is Cryptography. Usually in Hill cipher there are two keys, of which one acts as encryption key and the other one acts as decryption key.  In this paper we discuss about Hill Cipher using only one key for data encryption and data decryption. Further, we extend our result with dual encryption and decryption process which is explained by using the RSA public key cryptosystem and Hill Cipher and they together execute a powerful cryptosystem to secure the data. Objectives: The purpose of this paper is to obtain and compare the result of data encryption and data decryption using: A matrix which is invertible. A matrix which is Involutory. An RSA cryptosystem which is applied for Hill Cipher where the matrix is Involutory. Methods: Using Hill Cipher and thereafter Hill Cipher - RSA together we have encrypted and decrypted the data under modulo 255. Results: The text message is converted to coded message and then original message is retrieved by using the three different techniques. Conclusions: As the paper involves two stages of encryption and decryption where public key and private key which are unthinkable by the third parities, the security of information is highly appreciable.