International Journal of Communication and Computer Technologies Volume 01 – No.60 Issue: 07 Aug 2013 ISSN NUMBER : 2278-9723 Volume 01 – No.60, Issue: 07 Page 208 International Journal of Communication and Computer Technologies www.ijccts.org GPH Algorithm: Improved CBC improved BIFID cipher Symmetric Key Algorithm 1 Dinesh Goyal, 2 Naveen Hemrajani, 3 Kritika Paliwal 1,2,3 Department of Computer Science,Suresh Gyan Vihar University, ABSTRACT: Cryptography is art of illusion within which the sender encodes the message employing a key and sends it over the line. The receiver on the opposite facet of the channel decodes the message back and victimization the key tries to get back the initial message. In case the key throughout the communication is same on each side then it's referred to as radial key cryptography and if is termed as uneven key cryptography. There have been completely different secret writing techniques used for the plain text called as block & stream cipher. The modes for encryption are ECB, CBC, OFB & CFB. In this paper we propose a symmetric key algorithm using CBC mode of encryption with high complexity. Keywords: CBC, Symmetric Key, Bifid, Transposition. I. INTRODUCTION Cryptography: - cryptography is a science of knowledge security. Cryptography divided in to 2 Greek words “Crypto’s” means that “hidden” and “Graphos” means that “word”. It will outline a way to send encrypted or decrypted message. With the assistance of encrypted and decrypted message 2 individuals communicate one another firmly.[3] Cryptography is the art and science of non-public info protection from dangers of attacks, to convert it into a non-identifiable type their attacks. Primarily information encrypted content information, like text, images, audio, video, etc., to form information illegible, not visible or cannot be referred to as throughout scrambled transmission or storage of encrypted. Cryptography's main objective is to keep the info secure from unauthorized offender. [3] 1.1 There are 5 objective of cryptography[3]  Authentication  Secrecy or Confidentiality  Integrity  Non-Repudiation  Service Reliability and Availability 1.2 Modes of operation This section explains the four most common modes of operations in Block Cipher encryption-ECB and CBC, CFB, OFB with a quick visit to other modes.  Electronic Codebook (ECB) mode The simplest of the encryption mode is the electronic codebook (ECB) mode. The message is divided in to block and each blocks is encrypted separately. Electronic Codebook is DES native mode "direct application of the DES algorithm to encrypt and decrypt data. In this mode, each plaintext block is independently, to the corresponding cipher text block encryption. This is done through the Feistel password; it creates the basis of the 16 sub keys Symmetric key encryption transformation of plaintext through 16. The same process is used (symmetric key) back into plaintext into cipher text. Duplicate data blocks give same result in duplicate cipher text block.[5]. Fig.1 ECB (Encryption encoding)  Cipher Block Chaining (CBC) mode CBC mode of operation was invented by IBM In 1976. In cipher block chaining (CBC) mode each blocks has plaintext Cipher Block Chaining mode is a block cipher, XOR (exclusive OR) for each new Plaintext block with the previous cipher text block (they are "linked" together). This means that repeating plaintext block does not lead to duplication of cipher text blocks. CBC also uses an initialization vector, which is the initial use of a random function blocks, in order to ensure The results of two identical plaintext cipher text in different (due to different initialization Vectors).[2] Fig.2 CBC(Cipher Block chaining)  Cipher Feedback (CFB) mode Cipher feedback mode is a stream cipher to encrypt the plaintext into units X-bit (from 1-64). This allows the bit or byte level of encryption. CFB mode uses a random initialization vector, and the previous cipher text unit