BYTE ROTATION WITH CBC ENCRYPTION ALGORITHM

Transcription

1 BYTE ROTATION WITH CBC ENCRYPTION ALGORITHM MAHENDRAN R Assistant professor, Dept of computer science, Puthanampatti ABSTRACT In this modern electronic age we need to protect sensitive and valuable information related to an individual s corporation s commercial industries governments etc. In this connection the data encryption and decryption technique are playing an important role. Traditionally secured methods can be used to encrypt data s encryption techniques can be cracked but making as hard as possible to crack is the function of a good encryption techniques and also a good encryption algorithm should ensure that the all original information which are transformed from one end to another end. So there is a demand for a stronger encryption algorithm which very hard to crack there are various algorithm AES, DES, RSA, etc. But security level is depending on the time speed and complexity of algorithm (ie) as security level is increased. The time complexity algorithm is increased time and the speed is decreased. This is the major problem of decreasing speed and efficiency of the encryption system. Byte rotation with encryption algorithm is the new method which ensures security as well as speed of the encryption scheme. 1. INTRODUCTION Cryptography is an art of hiding information. A lot of research has been done in the field of cryptography. There are various encryption algorithms used for secure data transmission. The AES has been adopted as a Standard for Encryption by NIST (National Institute of Standards and Technology s). The conventional methods of encryption can only maintain the data security. The information could be accessed by the unauthorized users for malicious purpose. Therefore, it is necessary to apply effective encryption / decryption methods to enhance data security. The multiple encryption and multilevel encryption system provides sufficient security. But the performance and speed of these systems is low. Their complexity is very high. In this research paper, a new encryption algorithm named Byte Rotation withcbc Encryption Algorithm (BRCEA) is proposed which is applied on different blocks of plaintext 1.1 INTRODUCTION TO CRYPTOGRAPHY Cryptography is the study of transmitting secret messages securely from one party to another. To accomplish this task, the original text, called plaintext, is translated into an encrypted version called cipher text, which is sent to the intended recipient. The recipient decrypts the text to obtain the original message. Cryptography is considered not only a part of the branch of mathematics, but also a branch of computer science. There are three main forms of cryptosystems: Symmetric Encryption System, Asymmetric Encryption System and Hash Functions. These models of encryption have been developed to provide security of information but each of them having some merits and demerits. No single

2 algorithm is sufficient for this purpose. As a result researchers are working in the field of cryptography to remove the deficiency and finding better solution. In this paper, an effort has been made to develop a new algorithm BREA which is a block cipher and used with Block Wise Parallel Encryption Model [6]. The model has been written into two steps. In the first step, the plaintext has been broken into number of blocks. Each block size is of 16 bytes. So the number of blocks depends on the total input bytes of plaintext. Each block is represented by 2D array. These arrays of blocks are passed into BREA in parallel manner to execute simultaneously by using multithreading concept. The concept will allows all the blocks to process parallel in CPU. Because of parallel execution, the processing speed of the system will enhance. 2. BLOCK CIPHER AND STREAM CIPHER CRYPTANALYSIS 2.1 DEFINITION OF BLOCK CIPHER Block ciphers encrypt information by breaking it down into blocks and encrypting data in each block. A block cipher encrypts data in fixed sized blocks (commonly of 64 bits). Block Cipher 2.2. DEFINITION OF STREAM CIPHER A stream cipher consists of a state machine that outputs at each state transition one bit of information. This stream of output bits is commonly called the running key. The state machine is nothing more than a pseudo-random number generator.

3 3. CIPHER BLOCK CHAINING Cipher Block Chaining (CBC) uses feedback to feed the result of encryption back into the encryption of the next block. The plain-text is XOR' ed with the previous cipher-text block before it is encrypted. The encryption of each block depends on all the previous blocks. This requires that the decryption side processes all encrypted blocks sequentially. This mode requires a random initialization vector which is XOR' ed with the first data block before it is encrypted. The initialization vector does not have to be kept secret. The initialization vector should be a random number (or a serial number), to ensure that each message is encrypted uniquely. An error in an encrypted block (caused by e.g. a transmission failure) causes the block with the error to be completely garbled. The subsequent block will have bit errors at the same positions as the original erroneous block. The blocks following the second block will not be affected by the error. Hence, CBC is self-recovering. While CBC recovers quickly from bit errors, it does not recover at all from synchronization errors. If a bit is added or lost from the cipher-text stream, then all subsequent blocks are garbled. A system that uses CBC must therefore ensure that the block structure remains intact. Like the ECB mode, CBC also requires a complete block on its input before encryption can take place.

4 Cipher block chaining (CBC) is a mode of operation for a block cipher (one in which a sequence of bits are encrypted as a single unit or block with a cipher key applied to the entire block). Cipher block chaining uses what is known as an initialization vector (IV) of a certain length. One of its key characteristics is that it uses a chaining mechanism that causes the decryption of a block of ciphertext to depend on all the preceding ciphertext blocks. As a result, the entire validity of all preceding blocks is contained in the immediately previous ciphertext block. A single bit error in a ciphertext block affects the decryption of all subsequent blocks. Rearrangement of the order of the ciphertext blocks causes decryption to become corrupted. Basically, in cipher block chaining, each plaintext block is XORed (see XOR) with the immediately previous ciphertext block, and then encrypted.identical ciphertext blocks can only result if the same plaintext block is encrypted using both the same key and the initialization vector, and if the ciphertext block order is not changed. It has the advantage over the Electronic Code Book mode in that the XOR'ing process hides plaintext patterns. 4. PROPOSED BYTE ROTATIONWITH CBC ENCRYPTIONALGORITHM The steps of byte rotation with CBC encryption algorithm. 1. The letters of alphabet are assigned numerical values from 1 to 26 in sequence. i.e. A, B, C,. X, Y, Z assigned numeric values 1, 2, 3,..24, 25, 26 respectively represented matrix. 2. The plaintext is partitioned into fixed-length blocks of size 16 bytes cor 128 bits each. Tease blocks are represented by a matrix mp. 3. Calculated the transpose matrix of plain text block matrix (mp). Which is denoted by Mpt 4. The values of key matrix (k) are randomly selected from the range 1 to 26. The size of key matrix is equitant to the block size of plain text ie 16 byts. 5. Calculate encrypted key matrix ie using the following formula. Ke=K mod2 6. Apply for CBC algorithm (block cipher) in Ke, calculate the encryption key matrix Kc. 7. Add both matrix Mpt and Kc and the result matrix is denoted by cpk. Cpk =Mpt+Kc 8. Rotate first three rows horizontally if cpk matrix such that rotate the one byte from first row, two byte second row, three byte third row. The result matrix is denoted by Chr 9. Rotate the three column vertically of Chr matrix such that rotate the one byte first column, two byte second column, three byte third column. The result matrix is denoted by Cvr. 10. Replace the numeric values of Cvr corresponding letters. The result matrix is denoted by Ce. 5. IMPLMNTATION OF BREA

5 Example: In BREA, the letters of alphabets are assigned a numeric value as stated in the algorithm. Let the input plaintext is: HAI HAVE A NICE DAYS Its plaintext block matrix M can be represented as: H A I H M = A V E A N I C E D A Y S A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Now substitute numeric values of letters in the above block matrix as shown below: Mp = Find the transpose matrix of M p Mp T = Then, calculate Key matrix of size 16 bytes by random selection of any 16 numbers from 1 to 26 and

6 without reputation as given below: K=[k1,k2 k16] K=Random (1, 26, 16) K = Calculated Ke by using formula Kc= K mod Ke = Apply for CBC mode m= block size (n) = 4 bits Iv = 1010 =Co K =

7 C1 = ɛ k [m1 C0] = ɛ k [ ] = ɛ k [1110] C1=1110 C2 = ɛ k [m2 C1] = ɛ k [ ] = ɛ k [1010] C2=0101 C3 = ɛ k [m3 C2] = ɛ k [ ] = ɛ k [0100] C3=1000 C4 = ɛ k [m4 C3] = ɛ k [ ] = ɛ k [0100] C4=1000 Encryption key matrix Kc Kc = Add both matrix MP T and Kc and result matrix denoted by CPk

8 CPk = MP T + Kc CPk= CPk = Now horizontal rotate CPk = Chr =

9 Now vertically Chr = Cvr = Cvr is replaced by their corresponding alphabetic Ce = I J E L Y A O C L N A C B B E S Decryption is reverse process 6. CONCLUSION In our BRCEA system proposed a good strategy of most out of the advantage eliminates the limitations.the develops for the system in any network services for the network security. In this algorithm security will be high compare with BREA. The key matrix applies for CBC techniques encryption process and then after process will be continued. 7. FUTURE WORK

10 The system can be easily modified to accept any encryption algorithm. Just by adding or removing another module in the main function, any number of algorithms can be included. Moreover, we currently concentrate on our next work which adopts Parallelism through multiprocessor system where we can run various Encryption Algorithms in parallel environment which enhances the performance and speed of Encryption/ Decryption process. 8. REFERENCES 1. R.L.Rivest, A.Sharmir, L.Adleman : A method for obtaining digital signatures and public key Cryptosystems, Tata McGraw-Hill. 2. W. Stallings, Cryptography and Network Security: Principles and Practice 3/e. Prentice Hall. 3. Cormen, Thomas H, Charles E.Leiserson, aronald L.Rivest Clifford Stein Introduction to algorithms. MIT Press and McGraw-Hill. 4. Fbergeron,j.berstel,and S.Berlek, Efficient computation of addition chains.jounal de theorie des numbers Bordeaux francia.,6no.1:2-10, D.M Gordon A survey of fast exponentiation methods.techniqual report,center for communications Research,Westera court sandiego,ca Kaya-Koc. High-speed RSA implementation. Technical report, RSA Laboratories, Redwood City, CA, León-Javier, N. Cruz-Cortés, M.A. Moreno-Armendériz, and S.Orantes-Jiménez. Finding minimal addition chains with a particle swarm optimization algorithm. Lecture Notes in Computer Science, 5845/2009: , 2009.