# Multi Level Encryption Scheme For Security Enhancement Computer Science Essay

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ABSTRACT - In this Information era, where all the transactions and files are digitized, the need for secure channel is eminent for transactions and confidential files. Cryptographic algorithms play a dominant role in securing the files without getting attacked by the intruders. But in this current scenario there are numerous number of chances to break an encryption algorithm by performing cryptanalytic attacks. So the demand for a strong encryption algorithm becomes vital. It is obvious that if a message is encrypted by using more than one encryption algorithm then it cannot be easily breaked by the eavesdroppers. In this paper, we proposed a multi level of multiple encryption schemes which enhances the security of the algorithm.

## Keywords: Security, Cryptography, Encryption, Random Hash Function.

## INTRODUCTION:

For ensuring the security, the plain text is converted to cipher text and the process is called encryption. Although this conversion idea is old, the way of encryption should not be vulnerable to attacks. Caesar's cipher method, poly alphabetic substitution method, bit-level encryptions like substitution box, permutation box, encoding, rotation are some of the conventional encryption methods. These methods are easy to implement but can be cracked easily with the high end technologies. The objective of this project is to develop multi-level encrypter software that can be used to encrypt top-secret files including text, images and multimedia files in the secondary storage devices.

## 2.0 EXISTING SYSTEM:

Most of the existing systems are vulnerable to attacks and it is breaked at some point of time because of its platform dependency and the emerging trend of open software solutions. Despite some systems are developed to support cross platform, they do not use multi level encryption. Despite some systems support multiple encryptions, they do not use randomized encryption hence can be cracked after a period of time. Most of the existing systems support text encryption preferably than other media types.

## 3.0 PROPOSED SYSTEM:

We proposed a system which is developed in such a way that it should be platform independent. It is developed through multiple encryption algorithms. Plaintext is encrypted through an Encryption algorithm which transforms it into a cipher text. Thus obtained cipher text is supplied as plaintext for the next encryption algorithm which in turn produces an another cipher text and thus produced cipher text is fed as plain text to the next encryption algorithm and so on. This process continues depends upon the number of encryption algorithm used. We also use a Random function which generates a n-digit number based upon the n-number of Encryption algorithms used. Thus generated n-digit number determines the order of selecting Encryption algorithms. Another significant feature of this proposed system is it is developed in order to support not only text files but also images and media files.

## Fig.1: PROPOSED ARCHITECTURE

For simulating the system we adopted three famous cryptographic algorithms to implement multilevel security. The high feasibility with our system is it can suits any algorithm of any type. They are

Advanced Encryption System Algorithm,

Data Encryption Standard,

Rivest Shamir Adleman algorithm

## 3.1 AES ALGORITHM:

This algorithm is flexible in supporting any combination of data and key size of 128, 192, and 256 bits. However, AES merely allows a 128 bit data length that can be divided into four basic operation blocks. These blocks operate on array of bytes and organized as a 4Ã-4 matrix that is called the state. For full encryption, the data is passed through Nr rounds (Nr = 10, 12, 14) [4, 6]. These rounds are governed by the following transformations:

(i) Byte Substitution: This is a non linear byte Substitution, using a substation table (s-box), which is constructed by multiplicative inverse and affine transformation.

(ii) Shifting the rows: This is a simple byte transposition, the bytes in the last three rows of the state are cyclically shifted; the offset of the left shift varies from one to three bytes.

(iii) Mixing of columns: Is equivalent to a matrix multiplication of columns of the states. Each column vector is multiplied by a fixed matrix. It should be noted that the bytes are treated as polynomials rather than numbers.

(iv) Adding round key: Is a simple XOR between the working state and the round key. This transformation is its own inverse. The following diagram shows pictorial view of overall algorithm.

## 3.2 DES ALGROITHM:

DES is a block cipher which takes a fixed-length string of plaintext bits and transforms it into cipher text bit string of the same length. The key length of DES is 64 bits. DES Algorithm uses fiestal structure which performs the following operations

Expansion - By duplicating some of the bits, 32-bit block is expanded into 48 bit block by using the expansion permutation.

Key mixing -Expanded block is mixed up with a substitution key by using an XOR operation. Sixteen 48-bit sub keys are derived from the main key as one key for each round.

Substitution - After Key Mixing is over, the block is further divided into 6-bit pieces of eight blocks. By following Non liner transformation, each of the S-boxes replaces its six input bits with four output bits. S-boxes plays a important role in determining the security of the algorithm and without them the algorithm becomes linear and easily breakable.

Permutation -Thus after substitution 32 outputs from the S-boxes is rearranged by permutation.

## 3.3 RSA ALGORITHM:

RSA is an asymmetric cryptographic algorithm. Asymmetric means that there are two different keys. Sometimes this is also called public key cryptography, because one of the can be given to everyone. The other key must be kept private.RSA involves a public key and private key. The public key can be known to everyone, it is used to encrypt messages. Messages encrypted using the public key can only be decrypted with the private key. The keys for the RSA algorithm are generated the following way:

Pick two relatively prime numbers x and y

Calculate the value of n which is the modulus for the public and private keys by using the formula n=x*y

Determine the quotient :Q(n)= (x-1) (y-1).

Choose an integer i such that 1< i<<q(n),and integer i is co-prime to Q(n) that is 1is the only greatest common factor which divides i and Q(n) .

I and D are the public key and private key exponent respectively.\

Calculate D which satisfies the congruence relation: DI=1+Q (n)*K where K is a integer.

## Encryption:

Receiver provides its public key N and I to Sender and keeps its private key secret. Sender wants to transmit the secret message to receiver. At first Sender turns the secret message into a number which is smaller than n by adopting any padding scheme or any reversible protocol .hence the ciphertext can be calculated as

C=M I mod N

## Decryption:

Receiver can recover the secret message M from cipher text by using its private key d in the following formula

M= CD mod N.

## 4.0 SIMULATION:

## 4.1 Encryption and Decryption of text files:

## Fig.2: Home screen Fig.3: Browse window

## Fig 4: Encrypting text file Fig 5: Text file after encryption

## Fig 6: Text file after decryption

## 4.2Encryption and Decryption of image files:

## Fig 7: Encryption of Image Fig 8: Message :file cannot be opened

## Fig 9, 10: Decryption & Displaying of image file after decryption

## 5.0 FUTURE ENHANCEMENTS:

The system can be easily modified to accept any encryption algorithm which is framed in future.

Just by adding another module in the hash limit any number of algorithms can be included.

The system is designed for storage level but the modules can be used in web services also.

By adding a new button with a server and client sockets, the system can also be improved to work as secure LAN File messenger.

By adopting Parallelism, We can run various Encryption Algorithms in parallel environment which enhances the performance and time taken for Encryption/Decryption.

## 6.0 CONCLUSION:

So far we have discussions on various algorithms in cryptography. Each algorithm having its own advantages and disadvantages, this system proposed a good strategy of making most out of their advantage while trying to eliminate the limitations. The developed system ignoring the front end could be used in any network services for network security. The system also supports 64 bit operating systems which will be of future concern of all Operating System manufacturers. The concept of multi level encryption along with randomizer enhances the security of files. The system also proposed a way of encrypting media files. Thus the system is justified for its use in securing files.