Suhail Aslam Khaskheli 15MSM09 Supervisor Dr. Shakeel Ahmed Kamboh creator Department of Mathematics & Statistics text QUEST 2018 monographic 118 ABSTRACT The art of encryption and decryption of secret messages has gained much attention due to its indispensable uses in information security mainly in government and electronic commerce. The techniques can be classified into two main cryptographic methods namely, symmetric key (also called secret-key) and asymmetric key (also called public-key) methods. Due to the simplicity of symmetric key encryption algorithms they are efficiently applied in processing the confidential information and are found to be less computationally intensive as compared to asymmetric key algorithms. However, the main weakness of symmetric key encryption algorithms is the sharing of the same key that must be exchanged between the sender and the recipient. In addition, if the choice of symmetric keys is very limited then the brute force or cryptanalysis attack may easily break the encrypted message. This issue provides the motivation to investigate and develop a simple yet computationally secure symmetric key encryption/decryption algorithm. Therefore, in this study an encryption/decryption algorithm is proposed and developed . The developed algorithm is based on the idea of both stream and block cipher with the assumption that any given plaintext can be encrypted like a stream of cipher values with a combination of three encryption keys {ki, k2, kJ} that use any value between N={ l,2,3 ...n}. Then the cipher values can be used to make the blocks of alphabets containing only {A, B, C, D, E, F, G, H, I, J}, each block is separated by a space. The steps of algorithm could also be reversible for decryption of the cipher text. A MATLAB code is written to implement the algorithm and tested for three different input messages. The specialty of the algorithm is that it very flexible for any type of characters and is very simple in terms of mathematical operations as it uses only arithmetic operations and does not use modular arithmetic, matrices or other complicated mathematical operations. The performance of the algorithm is evaluated in terms of computational time, memory usage, frequency analysis, Index of Coincidence and computational complexity. From the analysis, it is found that the http://tinyurl.com/5eunz6w7 http://tinyurl.com/5eunz6w7