Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 1, Issue 3, September – October 2012 ISSN 2278-6856 Analysis of Avalanche Effect in Plaintext of DES using Binary Codes Akash Kumar Mandal1, Mrs. Archana Tiwari2 1Department of Electronics and Telecommunication Chhatrapati Shivaji Institute of Technology,,Durg,Chhattisgarh,India 2Department of Electronics and Instrumentation Chhatrapati Shivaji Institute of Technology,,Durg,Chhattisgarh,India Abstract: With the fast progression of digital data exchange and understood is called plaintext or clear text. The in electronic way, information security is becoming more method of scrambling the plaintext in such a way that important in data storage and transmission. Cryptography hides its substance is called encryption. Encrypting has come up as a solution which plays a vital role in plaintext makes the information in unreadable information security system against malicious attacks. This information called cipher text. The process of converting security mechanism uses some algorithms to scramble data into unreadable text which can be only being decoded or cipher text to its original information is called decryption. decrypted by party those possesses the associated key. These The complexity of encryption process depends on algorithms consume a significant amount of computing algorithm used for encryption, software used and the key resources such as CPU time, memory and computation time. used in algorithm to encrypt or decrypt the data. Security In this paper a most widely used symmetric encryption of any encryption system depends on the security technique i.e. Data Encryption Standard (DES) have been principle proposed by Kirchhoff. According to the implemented using MATLAB software. After the implementation, this encryption technique was analyzed Kirchhoff, the security of the encryption system should based on a parameter called Avalanche effect, using binary depend on the secrecy of the encryption /decryption key codes. Avalanche Effect due to one bit variation in plaintext rather than encryption algorithm. [3] keeping the key constant after mapping it in a binary code, After extensive survey of various research papers it is Experimental results shows that the proposed algorithm observed that an encryption algorithm should produce exhibit significant high Avalanche Effect which improves the significant change in the encrypted message when a small level of the security. change is made in original message. Keywords: Data Encryption Standard (DES), Encryption, Decryption, Ciphertext, Secret key, Avalanche Effect. 1. INTRODUCTION Transmission of sensitive digital data over the communication channel has emphasized the need for fast and secure digital communication networks to achieve the requirements for integrity, secrecy and non reproduction of transmitted information. Cryptography provides a method for securing and authenticating the transmission of information across insecure communication channels. Figure.1 Overview of the field of cryptography It enables us to store sensitive information or transmit it over insecure communication networks so that In research papers [8] and [9] authors analyzed various unauthorized persons cannot read it. [1] Cryptography is cryptographic algorithms using a parameter called an indispensable tool for protecting sensitive information Avalanche Effect. In this paper we proposed an in computer systems. Cryptography makes the message enhancement in DES algorithm using binary codes. This unintelligible to outside the world by various proposed algorithm is expected to provide significant transformations. Data Cryptography is method of high Avalanche Effect. scrambling the content of digital data like text, image, audio and video to make it unreadable or unintelligible 2. CRYPTOGRAPHIC ALGORITHMS for others during transmission. The main goal of Depending upon the number of keys used, cryptographic cryptography is to keep the data secure from unauthorized algorithms can be classified as asymmetric algorithms access [2]. Data containing information that can be read (public key) and symmetric algorithms (secret key). In Volume 1, Issue 3, September – October 2012 Page 166 Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 1, Issue 3, September – October 2012 ISSN 2278-6856 Symmetric keys encryption or secret key encryption Data can be recovered from cipher only by using exactly identical key is used by sender and receiver. Data the same key used to encipher it. Unauthorized recipients Encryption Standard (DES), 3DES, and Advanced of the cipher who know the algorithm but do not have the Encryption Standard (AES) are the example of correct key cannot derive the original data Symmetric key encryption algorithms. In asymmetric algorithmically. However, it may be feasible to determine keys encryption two different keys (public and private the key by a brute force “Exhaustion attack” Also, anyone keys) are used for encryption and decryption. Public key who does have the key and the algorithm can easily is used for encryption and private key is used for decipher the cipher and obtain the original data. A decryption Rivest-Shamir-Adelman (RSA) and Elliptic standard algorithm based on a secure key thus provides a Curve Cryptosystem (ECC) are the example of basis for asymmetric key algorithms.[4]A symmetric cryptosystem has five ingredients: 2.1 Plaintext This is the original data or message to be transmitted that fed into the algorithm as input. 2.2 Encryption Algorithm The algorithm performs various transformations and substitutions on the plaintext. 2.3 Secret key This is another input to the algorithm and the value of secret key is independent of the plaintext. Depending on the specific key the algorithm will produce a different output. 2.4 Encryption Algorithm This is the scrambled or encrypted message produced as output. This output depends on the plaintext and the Figure 2 DES (Data Encryption Standard) process secret key.[5] 2.5 Decryption Algorithm Input plaintext Encryption key This is essentially the encryption algorithm operate in reverse. It takes the ciphertext and the secret key as input and produces the original plaintext as output. Binary Codes Binary Codes 3. DES ALGORITHM The Data Encryption Standard (DES) designed to encrypt Encryption Algorithm and decrypt blocks of data consisting of 64 bits under (DES) control of a 64-bit key. Encrypting data converts it to an unreadable cryptorgaphic security of the data depends on the security provided for the key used to encipher and decipher the data. [4]form known as cipher. Decrypting Ciphertext cipher converts the data back to its original form known as plaintext. Both encryption and decryption operations Figure 3 DES process when input plaintext and input key are performed using a binary number called a key. A DES are mapped in binary code key is a 64 bit binary number of which 56 bits are randomly generated and used directly by the algorithm. exchanging encrypted computer data by issuing the key The remaining 8 bits, which are not used by the used to encipher it to those authorized to have the data. algorithm while encryption, can be used for error Data that is considered sensitive by the responsible detection. The 8 error detecting bits are set to make the authority, data that has a high value, or data that parity of each 8-bit byte of the key odd, i.e., there is an represents a high value should be cryptographically odd number of "1"s in each 8-bit byte. Authorized users protected if it is vulnerable to unauthorized disclosure or of encrypted computer data must have the key that was undetected modification during transmission or while in used to encipher the data in order to decrypt it. The storage. [6] encryption algorithms specified in this standard are commonly known among those using the standard. The Volume 1, Issue 3, September – October 2012 Page 167 Web Site: www.ijettcs.org Email: [email protected], [email protected] Volume 1, Issue 3, September – October 2012 ISSN 2278-6856 4. METHODOLOGY the plaintext or the key should produce a significant change in the cipher text. We have implemented Data Encryption Standard (DES) algorithm in MATLAB 7.0 software. This encryption Numberof flippedbitsincipheredtext AvalancheEffect technique takes 64 bit data block as input and encrypt this Numberof bits in ciphered text data block using 64 bit key. Figure 3 shows the block diagram of algorithm that we have used for our However, a change in one bit of the plaintext or one bit of experiments. In our experiments we have mapped input the key should produce a change in many bits of the plaintext and encryption key into various binary codes cipher texts. This property is known as Avalanche Effect before providing the input to the DES algorithm. [8, 9].Avalanche Effect can be calculated by using above If there are n quantities in a group, a code of b binary equation. digits or bits may represent all quantities unequally. [7] The performance of proposed algorithm is evaluated n b using Avalanche Effect due to one bit variation in plaintext(before being mapped in various binary codes) 4.1 Natural BCD Code (8421 code) keeping encryption key constant in a binary code . Natural BCD code or 8421 code is used whenever Avalanche Effect is calculated for various combination of decimal information is transferred in or out of a digital plaintext and encryption key by mapping them in various system. In this code straight assignment of binary binary codes. equivalent is used with weights. Table 1: Data code is fixed in 2421 code and key varied 4.2 2421 Code Key : '3B3898371520F75E' Data in Avalanche These are weighted ,reflected and self-complementing Data:'ABCDEF01 Data:'ABCDEF01 2421 Effect codes, In 2421 codes if a number has more than one 23456789' 27456789' 'C79E3C7 '2A8EA04C 2421 37 representation then choose the code that uses the lower A3E1763CF' 65B41C60' 'B466EBF3 '778AD655 binary weights (for number 0-4 only) 3321 35 64DB1F96' 703CF8A7' '194DBB9E 'AAADCE33 4.3 5421 Code 4221 35 9849A99D' FE7F47B7' These are weighted code with weight 5-4-2-1.