1 Abstract— The demand for adequate security to electronic data systems grows high over the decades. As the security issue also impact on the performance analysis of the wireless network, data encryption is necessary for sending and receiving information secretly over the network. Since 1970s, Data Encryption Standard (DES) has received a substantial amount of attention from academic cryptanalysts. However, in 1998 it has been proved insecure and on October 2000, National Institute of Standards and Technology (NIST) announced that the Rijndael algorithm was selected as the Advance Encryption Standard (AES). Our proposed algorithm is based on Rijndael algorithm, which encrypts block of 200 bits using symmetric keys of 200 bits. This algorithm has been implemented on random mobility model and the performance results have been summarized with a conclusion in this paper. Keywords—: Block cipher, symmetric encryption, random mobility, MANET. I. INTRODUCTION The selective application of technological and related procedural safeguards is an important responsibility of every organization in providing adequate security to its electronic data systems. Protection of data during transmission or while in storage may be necessary to maintain the confidentiality and integrity of the information represented by the data. The algorithm uniquely defines the mathematical steps required to transform data into a cryptographic cipher and also to transform the cipher back to the original form. Our proposed algorithm is much more similar to that of Rijndael. The difference is that, in Rijndael algorithm the block size start from 128 bits and then increase by appending column [1] but in our algorithm the block size start from 200 bits. First we present the mathematical basis necessary for getting the algorithm properly followed by the description itself and then give the simulation result of time comparison between the original Rijndael implementation on 128bits block size having 128 bits key and our proposed algorithm which operate on 200 bits block size having 200 bits key size. II. MATHEMATICAL PRELIMINARIES Several operations in Rijndael are defined at byte level with bytes representing elements in the finite field GF (2 8 ). The basic mathematical concept needed to get the proposed algorithm is given in [3]. III. PROPOSED ALGORITHM As the security is the function of block length and the size of key length, we increase the block length as well as the key length. Our basic block length is 200 bits, which can be shown as a 5 by 5 matrix of byte. We can increase our block by appending a column at a time but here we emphasize on 200 bits. A. Definition The intermediate cipher result is called the State. The State can be pictured as a rectangular array of bytes. This array has five rows; the number of columns is denoted by Nb and is equal to the block length divided by 40. The input and output used by our proposed algorithm at its external interface are considered to be one dimensional arrays of 8-bit bytes numbered upwards from 0 to the 5*Nb- 1.The Cipher Key is considered to be a one-dimensional arrays of 8-bit bytes numbered upwards from 0 to the 5*Nk-1. The cipher input bytes (the “plaintext” if the mode of use is ECB encryption) are mapped onto the state bytes in the order a 0,0 , a 1,0 , a 2,0 , a 3,0 , a 4,0 , a 0,1 , a 1,1 , a 2,1 , a 3,1 , a 4,1 ... , and the bytes of the Cipher Key are mapped onto the array in the order k 0,0 , k 1,0 , k 2,0 , k 3,0 , k 4,0 , k 0,1 , k 1,1 , k 2,1 , k 3,1 , k 4,1 ... At the end of the cipher operation, the cipher output is extracted from the state by taking the state bytes in the same order. Hence if the one-dimensional index of a byte within a block is n and the two dimensional index is ( i ,j ), we have: i = n mod 5; j= n/5 ; n=i+ 5* j A Symmetric Data Encryption Algorithm for Increasing Security Md. Monir Hossain Mia, Md. Foizul Islam, M.A. Matin, Md. Nazrul Islam