International Journal of Computer Applications (0975 – 8887) Volume 103 – No.3, October 2014 13 Advanced Feedback Encryption Standard Version-1 (AFES-1) Debdeep Basu Department of Computer Science St. Xavier’s College(Autonomous) Kolkata, India Ankita Bose Department of Computer Science St. Xavier’s College(Autonomous) Kolkata, India Surajit Bhowmik Department of Computer Science St. Xavier’s College(Autonomous) Kolkata, India Saptarshi Chatterjee Asoke Nath Department of Computer Department of Computer Science Science St. Xavier’s St. Xavier’s College(Autonomous) College(Autonomous) Kolkata, India Kolkata, India ABSTRACT In this paper, Advanced Feedback Encryption Standard Version 1 (AFES-1), Nath et al have combined both bit-level and byte level operations on the plain text. Nath et al had recently published Multi Way Feedback Encryption Standard Ver-3 MWFES-3[5]. MWFES-3 is a byte level encryption algorithm. The authors have capitalized on the strength of MWFES-3[5] by introducing a bit-shuffling operation at the beginning of each iteration. At the beginning of each iteration, the plain text bits of that iteration are shuffled by using 24 different shuffling functions. Now, the order in which the 24 different functions are called, changes at each iteration, and that order is taken as a function of the key. After the initial shuffling of the bits, the bits are converted back to bytes and MWFES-3 is applied on the bytes. This process goes on Encryption Number (EN) times, where EN is also taken as a function of the key. So, at the beginning of each iteration, the bits obtained from the last iteration are shuffled in a different way. This method has been tested on standard plain texts such as ASCII ‘0’, ASCII ‘1’ and the results are quite satisfactory. This method is immune to any classical form of attacks. General Terms Encryption, Decryption. Keywords MWFES-I, MWFES-2, MWFES-3, Encryption Number. 1. INTRODUCTION Due to the tremendous development in internet technologies it is essential to encrypt any kind of confidential message before sending the message from one computer to another computer. Data security is an extremely important issue and many algorithms have been developed which are almost impossible to break. The intention of the trespasser is to break the cipher and to retrieve unauthorized information. It is the job of the cryptographers to restrict the trespassers from achieving unauthorized access. Nath et al had recently proposed MWFES-1[1], Modified MWFES-1[2], MWFES-2[3], Modified MWFES-2[4], MWFES-3[5]. In MWFES-1, the plain text character is added with the corresponding key character, the forward feedback and backward feedback and then the total sum (modulo 256) is taken as the corresponding cipher text character. The cipher text character is taken as the forward feedback value for the next byte (in case of forward operation) or backward feedback value for the previous byte (in case of backward operation). Forward and Backward operations are carried out on all the bytes starting from their respective ends. In MWFES-2, the process is a little more general. Instead of propagating the feedback to the next byte (in case of forward feedback) and to the previous byte (in case of backward feedback) the feedback is propagated to the n th byte where n is the ‘skip factor’. In MWFES-2 the forward skip is kept equal to the backward skip (equal to n) and the initial forward feedback value and the backward feedback value was kept 0. In MWFES-3, the authors introduced several changes in the algorithm. The plain text is broken into blocks and the encryption method is applied on each block separately. Each block has different Forward Skip (FS), Backward Skip (BS), initial Forward Feedback (FF) and initial Backward Feedback (BF) which are determined from the keypad counterpart of the block. These four important variables would decide the nature of the cipher text. The block size is different in every round of processing, causing these four important variables to change in every round. The total number of rounds (encryption no), and the block size value were also taken as a function of the key. In the present algorithm, i.e. AFES-1 the Plain Text is converted to its corresponding bits and stored in a square matrix of size equal to the integral square root of the number of bits. The residual bits remain untouched. Then the bits are arranged by calling 24 different shifting functions. Now, the order of calling the 24 functions change at each iteration and