International Journal of Applied Information Systems (IJAIS) – ISSN : 2249-0868 Foundation of Computer Science FCS, New York, USA Volume 2– No.2, February 2012 – www.ijais.org 15 Hybrid Security Algorithms for Data Transmission using AES-DES Jignesh R Patel PG-scholar,TCET Kandivali,mumbai india Rajesh S. Bansode Asst.prof, TCET Kandivali,mumbai india Vikas Kaul Asst.prof, TCET Kandivali,mumbai india ABSTRACT The fast evolution of digital data exchange has forced the information security to be of much important in data storage and transmission. As large amount of data is transmitted over the network, it is preliminary to secure all types of data before sending them. The problem with AES, most extensively used encryption is that it uses many multi variant equations which are linear in nature. Thus it can be broken using algebraic cryptanalysis. This provides a serious threat as AES was considered to be unbreakable and thus it was used in many encryption systems. The current paper presents the design and implementation of a hybrid based 128 bit key AES-DES algorithm as a security enhancement. Keywords Cipher, DES, AES, Hybrid AES DES, Key matrix. 1. INTRODUCTION The DES (Data Encryption Standard) is a cryptographic standard. The algorithm is designed to encipher and decipher blocks of data consisting of 64 bits under control of a 64-bit key. In cryptography, the Advanced Encryption Standard (AES) cipher has a 128-bit block size, with key sizes of 128, 192 and 256 bits, respectively. The integration of AES with DES is to enhance security for input mode as text ,image, audio and video. The paper outlines the possible weaknesses within the current AES encryption algorithm especially against algebraic based cryptanalysis. To understand the need for minimizing algebraic attacks on AES there by the idea of integrating AES with DES is proposed. Hence the development of the Hybrid AES-DES algorithm. 1.1 Cryptanalysis of AES AES is based on a design principle known as a Substitution permutation network. It is fast in both software and hardware. Unlike its predecessor DES, AES does not use a Feistel network[12]. AES has a fixed block size of 128 bits and a key size of 128, 192, or 256 bits, whereas Rijndael can be specified with block and key sizes in any multiple of 32 bits, with a minimum of 128 bits. The block size has a maximum of 256 bits[7]. AES operates on a 4×4 column-major order matrix of bytes, termed the state (versions of Rijndael with a larger block size have additional columns in the state). Most AES calculations are done in a special finite field. The AES cipher is specified as a number of repetitions of transformation rounds that convert the input plaintext into the final output of cipher text. Each round consists of several processing steps, including one that depends on the encryption key. A set of reverse rounds are applied to transform cipher text back into the original plaintext using the same encryption key[13]. The key size used for an AES cipher specifies the number of repetitions of transformation rounds that convert the input plain text into the final output, called the cipher text. The number of cycles of repetition are as follows:  10 cycles of repetition for 128-bit keys.  12 cycles of repetition for 192-bit keys.  14 cycles of repetition for 256-bit keys[5]. 1 .2 DES DES is the block cipher algorithm that takes a fixed-length string of plaintext bits and transforms it through a series of complicated operations into another cipher text bit string of the same length. In the case of DES, the block size is 64 bits. DES also uses a key to customize the transformation so that decryption can be performed by authentic user used to encrypt the key. The key ostensibly consists of 64 bits however only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits, and it is never quoted as such. Every 8th bit of the selected key is discarded, that is, positions 8, 16, 24, 32, 40, 48, 56, 64 are removed from the 64 bit key leaving behind only the 56 bit key [17]. The F-function, operates on half a block (32 bits) at a time and consists of four stages: 1. Expansion — The 32-bit half-block is expanded to 48 bits using the expansion permutation by duplicating half of the bits. The output consists of eight 6-bit(8*6=48bits) chunk, each containing a copy of 4 corresponding input bits, plus a copy of the immediately adjacent bit from each of the input pieces to either side[17].