Image Cipher Technique for Covert and Low Bandwidth Channels

Sangeeta Solanki1, A.K.Vats1, Shikha Maan1

(Corresponding Author: Sangeeta Solanki)

School of computer engg & IT. Shobhit University, Meerut, U.P. 250110, India1

(Email: solankisangeeta10@gmail.com) Abstract: Security of images during the transmission over

covert low bandwidth channel has importance in today's image communications for confidential, integrated and secure real time communication. The major security problems during communication over covert and low bandwidth channel is to reduce no of bits, efficient and secure cryptographic techniques such that output gain and performance may lead towards more secure and efficient mechanism. Thus, in this paper, we have purposed a secure, reliable and efficient mechanism using arithmetic coding techniques followed by IMAES (Improved Modified Advanced Encryption standard) techniques. The output of encrypted images reveals that proposed technique presents higher performance, quit reliable and robust.

Keywords: AC, AES, MAES, IMAES

1. INTRODUCTION 1.1 Cryptography

Cryptography is the practice and study of hiding information. Modern cryptography intersects the disciplines of mathematics, computer science, and electrical engineering. Applications of cryptography include ATM cards, computer passwords, and electronic commerce. It is the art or science of keeping secrets secret. It is about secure communication through insecure channels. It is a branch of cryptology dealing with the design of algorithms for encryption and decryption, intended to ensure the secrecy and authenticity of messages.

1.2 Cryptographic Confidentiality Technique

Cryptographic technique is the technique which is used for converting the plain text into cipher text and vice versa.

Key Key

Plain Text Cipher Text Plain Text

Fig 1: Block Diagram of Cryptographic System Cryptographic technique falls into two categories:

1.2.1 Symmetric Encryption Technique Symmetric or Conventional Encryption Technique uses

same key for encryption as well as decryption. A plain text is encrypted by Ks (secret key) gives cipher text & then cipher

text is decrypted again using the same key to produce output. A secret key can be a number, a word, or just a string of random letters. Secret key is applied to the information to change the content in a particular way. This might be as simple as shifting each letter by a number of places in the alphabet. Symmetric algorithms require that both the sender and the receiver know the secret key, so they can encrypt and decrypt all information. In this paper we use symmetric encryption technique for encrypting the plain text into cipher text and cipher text into plain text. There are various symmetric encryption algorithms as AES/ Rijndael, Blowfish, DES ,IDEA,RC2,RC4,RC6,Serpent, Triple DES, Two fish etc.

1.2.2 Asymmetric Encryption Technique

Asymmetric or Public Encryption Technique uses one key for encryption & another key for encryption decryption. A plain text is encrypted by Ka (public key) gives cipher text & then cipher text is decrypted using Kb (public key) to produce output. Asymmetric encryption uses different keys for encryption and decryption. The decryption key is very hard to derive from the encryption key. The encryption key is public so that anyone can encrypt a message. However, the decryption key is private, so that only the receiver is able to decrypt the message. It is common to set up "key-pairs" within a network so that each user has a public and private key. The public key is made available to everyone so that they can send messages, but the private key is only made available to the person it belongs to. The sender and the recipient must have the same software. Public key can be used by anyone with the same software to encrypt a message. The sender does not need the recipient's password to use his or her public key to encrypt data. The recipient's other key is a private key that only he or she can use when decrypting the message. There are various symmetric encryption algorithms as RSA, ECC, Elgamal etc.

1 .3 Image “An image may be defined as a two dimensional function

f(x, y), where x and y are spatial (plane co-ordinates. The amplitude of ‘f’ at any pair of co-ordinate (x, y) is called the intensity ‘or’ gray level of the image at that point”. It can also be defined as visual representation of something: as a likeness of an object produced on a photographic material or a picture produced on an electronic display (as a television or computer screen). In a mathematical context an image is a set of values

Encryption Algorithm

Decryption Algorithm

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given by a mathematical function (as a homomorphism) that corresponds to a particular subset of the domain. There are various categorization of image.

1.4 Covert Channel Covert channels [5] are not the most well known source of

risks, and are in fact totally ignored by the public, but they constitute a real threat. Several definitions of covert channels exist a covert channel is a mechanism that can be used to transfer information from one user of a system to another using means not intended for this purpose by the system developers. [NCSC TCSEC] defines a covert channel as any communication channel that can be exploited by a process to transfer information in a manner that violates the system's security policy. Covert channels pose a problem for highly secure environments such as government agencies and military ones. In multilevel security environments where users with high security levels must not be able to pass information to users with lower security levels, covert channels can be used to circumvent such policies. In a more classical environment, covert channels can be used by an attacker to communicate stealthy with a compromised machine, thus complicating the detection of the attack. This channel cannot provide security over the data [13].This channel does not have more capacity to travel the data in huge amount of bits, it can transmit the data in very less number of bits. This is the reason why the intruder can analyze the traffic or transmission of data in the form of bits.

1.5 Paper Organization In chapter 1, we have discussed regarding introduction to

Cryptographic Confidentiality Technique, covert Channels. In chapter 2 we undergoes through literature survey called related work, subsequently in chapter 3 we have given the solution named as proposed work. Then the mechanism of the proposed work is given in chapter 4. In chapter 5 we finally conclude this paper and chapter 6 gives the future scope.

1.6 Problem Identification We have identified a problem of security for image

information transmitted over covert channel and low bandwidth channels, so a encryption technique is required which provide security against different cryptographic attacks like brute force attack, statistical attack, meet in middle attack etc. Also there is a need of compression when there is a channel having low bandwidth so we purpose a security architecture and mechanism for providing effective and secure transmission.

2. RELATED WORK 2.1 Arithmetic Coding

It is shown that Arithmetic Coding [15] is the most powerful technique for statically loss less encoding. A message is coded as a real number in an interval from 1 to 0 for data. Arithmetic Coding typically has a better compression ratio, as it produces a single symbol rather than several separate code words. Although AC offers high efficiency in coding, it provides less or no security as conventionally implemented. While Arithmetic Coding is extremely efficient, the issue of

providing both security and compression simultaneously is growing more important and is given the increasing ubiquity of compressed image files in host applications of Defense, Internet and digital cameras and the common desire to provide security in association with these files. When both security and compression are sought, one approach is to simply use Arithmetic Coder (AC) in combining with Advanced Encryption Standard (AES).

Fig 2: Block diagram of image transmission and reception scheme As illustrated in figure 2 first the buffered image is

compressed by using arithmetic coder [15] followed by AES [15] encryption then the same process is repeated for decrypting the buffered image as first the image is decrypted using AES decrypter then with the help of arithmetic decoder the image is decompressed so that the original size of the image is regained.

Unlike the variable-length codes, Arithmetic Coding generates single code word. I.e. Arithmetic Coder does not generate code words one-to-one correspondence between source symbols and code words. Instead, an entire sequence of source symbols is assigned a single Arithmetic Code word. The code word lies between interval of real numbers 0 and 1[26]. As the number of symbols in the input increases, the interval used to represent it becomes smaller and the number of bits required to represent the interval becomes larger. Each symbol of the message reduces the size of the interval in accordance with the probability of occurrence.

2.2 AES Algorithm Rijndael is a block cipher developed by Joan Daemen and

Vincent Rijmen. The algorithm is flexible in supporting any combination of data and key size of 128, 192, and 256 bits [15]. 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 4×4 matrix that is called the state. These blocks operate on array of bytes and organized as a 4×4 matrix that is called the state [15]. For full encryption, the data is passed through Nr rounds (Nr = 10, 12, and 14) .These rounds are governed by the following transformations:

1) Sub Byte transformation: Is a non linear byte Substitution, using a substation table (s-box), which is constructed by multiplicative inverse and Affine Transformation.

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2) Shift rows transformation: 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.

3) Mix columns transformation: 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.

4) Add round key transformation: Is a simple X-OR between the working state and the round key. This transformation is its own inverse.

The problem with AES was that it is not able to provide higher level security and is not applicable for real time application as well as it is time consuming whenever an image is encrypted by it.

2.3 Key expansion With AES encryption, the secret key is known to both the

sender and the receiver. The AES algorithm remains secure; the key cannot be determined by any known means, even if an eavesdropper knows the plaintext and the cipher text. The AES algorithm is designed to use one of three key sizes (Nk). AES-128, AES-196 and AES-256 use 128 bit (16 bytes, 4 words), 196 bit (24 bytes, 6 words) and 256 bit (32 bytes, 8 words) key sizes respectively. These keys, unlike DES, have no known weaknesses. All key values are equally secured thus no value will render one encryption more vulnerable than another. The keys are then expanded via a key expansion routine for use in the AES [1] cipher algorithm. This key expansion routine can be performed all at once or ‘on the fly’ calculating words as they are needed. It is extremely fast compared to other block ciphers. (Though there is tradeoff between sizes and speed). The round transformation is parallel by design. This is important in dedicated hardware as it allows even faster execution. AES was designed to be amenable to pipelining. The cipher does not use arithmetic operations so has no bias towards big or little endian Architectures. AES is fully self-supporting. But it does not use S-Boxes of other ciphers, bits from Random tables .It is not based on obscure or not well understood processes. The tight cipher and simple design does not leave enough room to hide a trap door.

2.4. Improved Modified AES (MAES) MAES [1] overcome AES which lacked at security and were

also not applicable for real time application so a modification was done in it by adjusting the shift row phase. It reflected a high level security and better image encryption. The modification is done by adjusting the Shift Row phase. The modification is done as first it is examined whether the value in the first row and first Column, (state [0][0]) is even or odd. If it is odd, The Shift Rows step operates on the rows of the state; it cyclically shifts the bytes in each row by a certain offset. For MAES, the first and third rows are unchanged and each byte of the second row is shifted one to the left. Similarly, the fourth row is shifted by three to the left respectively. If it is even, The Shift Rows step operates on the rows of the state; it cyclically shifts the bytes in each row by a certain offset. The first and fourth rows are unchanged and each byte of the second row is

shifted three to the right. Similarly, the third row is shifted by tow respectively on to the right.

3. PROPOSED WORK

3.1 Illustration of IMAES with AC In [15], a combination of AES with Arithmetic Coder was

used and the given system provides simultaneous compression and encryption with negligible coding efficiency by accelerated hardware implementations but the system lacked in security when applied to real time applications so we purpose a architecture that is more secure and results in better performances for real time applications.

Fig 4: Block diagram of image transmission and reception scheme In the purposed Fig 4 the buffered image is compressed by

using arithmetic coder [15] followed by IMAES encryption then the same process is repeated for decrypting the buffered image as first the image is decrypted using IMAES decrypter then with the help of arithmetic decoder the image is decompressed so that the original size of the image is regained.

3.2 IMAES ( Improved Modified Advanced Encryption Standard)

MAES is a modified advanced encryption standard [15] that gives better encryption results in terms of security against statistical attacks. Here we have purposed the architecture of IMAES which can use a keys of length 128,192 and 256 bits by using RC4 [22] key generation algorithm. In this the modification is done by adjusting the Shift Row phase. In the Shift Row phase, if the value in the first row and first column is even, the first and fourth rows are unchanged and each bytes in the second and third rows of the state are cyclically shifted right over different number, else the first and third rows are unchanged and each byte of the second and fourth rows of the state are cyclically shifted left over different number of bytes. In this we have performed substitution on the input followed by permutation and finally applying multiplicative inverse on it. This modification allows for greater security and increased performance.

3.2.1 Phases of IMAES

3.2.1.1 Key Expansion phase The IMAES algorithm takes the Master Key K, and

performs a Key Expansion routine to generate a key schedule using RC4 key generation technique. The Key Expansion generates a total of 13 sub-key arrays of 16 words

Image buffer

Image buffer Arithmetic Decoder

Arithmetic Coder

IMAES Decryption

IMAES Encryption IMAES Encryption

IMAES Decryption

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of 8 bits taking into account that the first sub-key is the initial key. SP-Box is a non-linear and invertible product cipher table which is used to perform a one-by-one substitution and permutation of a byte value. Firstly substitution is performed on the states and then permutation takes place on the bytes independently.

a) Add Round Key Phase

The Add Round Key phase performs an operation on the State with one of the sub-keys. The operation is a simple XOR between each byte of the State and each byte of the sub-key.

b) Sub Byte phase

The Sub Byte transformation is a non-linear byte substitution followed by permutation that operates independently on each byte of the State using the SP Box table.

c) Shift Row phase

In the Shift Row transformation [1], the bytes in the last three rows of the State are cyclically shifted over 1, 2 and 3 bytes, respectively. The first row is not shifted

Instead of the original Shift row, we modify it as: 1. Examine the value in the first row and first column

(state [0][0]) is even or odd? 2. If it is odd, The Shift Rows step operates on the rows

of the state; it cyclically shifts then bytes in each row by a certain offset. For IMAES, the first and third rows are unchanged and each byte of the second row is shifted one to the left. Similarly, the fourth row is shifted by three to the left respectively.

3. If it is even, The Shift Rows step operates on the rows of the state; it cyclically shifts the bytes in each row by a certain offset. The first and fourth rows are unchanged and each byte of the second row is shifted three to the right. Similarly, the third row is shifted by tow respectively on to the right. d) Mix Columns phase

The Mix Columns transformation operates on the State column by column, treating each column as a four-term polynomial. The columns are considered as polynomials over GF (28)

and multi- plied by a fixed polynomial a(x) modulo x4+1 given by

a(x) = {03}x3 + {01}x2 + {01}x +{02} (1)

The matrix multiplication for this can be written as: S’(x) =A(x) S(x) s’0,c

s’1,c s’2,c s’3,c

= 02 03 01 01 s’

0,c 01 02 03 01 s’

1,c 01 01 02 03 s’

2,c 03 01 01 01 s’

3,c for 0≤c ≤4 (2) As a result of this multiplication, the four bytes in a column

are replaced as follows: S’

0, C = ([02].S0,C) .([03].S1,C) S2,C S3,C (3) S’

1,= S0,C ([02] .S1,C) ([03] .S2,C) S3,C S’

2,C = S0,C S1,C ([02].S2,C) ([03].S3,C) S’

3,C = ([03] .S0,C) S1,C S2,C ([02].S3,C) Where is the XOR operation and. is a multiplication

modulo the irreducible polynomial M(x) = x8+ x4+ x3+x+1. The below figure shows the

implementation of the function B= x time (A) which will be used to make the multiplication of the number by 2 modulo M(x). So, it will only have binary operations as :

[02]. S’X,C = Xtime(S’

X,C) [03]. S’

X,C= X time(S’X,C) S’

X,C

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Plain Text

S00 S10 S20 S30 S’

00 S’10 S’

20 S’30

S01 S11 Sij S31

S-Box S’01 S’

11 S’ij S’

31

S02 S12 S22 S32 S’02 S’

12 S’22 S’

32 S03 S13 S23 S33 S’

03 S’13 S’

23 S’33

S00 S10 S20 S30

S’00 S’

10 S’20 S’

30 S01 S11 S21 S31

S’11 S’

21 S’31 S’

01 S02 S12 S22 S32 S’

02 S’12 S’

22 S’32

S03 S13 S23 S33 S’

33 S’03 S’

13 S’23

S00 S10 S0j S30

S’00 S’

10 S’20 S’

30 S01 S11

S1j S31 S’

01 S’11 S’

1j S’31

S02 S12 S2j S32 S’02 S’

12 S’2j S’

32 S03 S13 S3j S33 S’

03 S’13 S’

3j S’33

S00 S10 S0j S30 K0j S’

00 S’10 S’

0j S’30

S01 S11 S1j S31 K1j S’

01 S’11 S’

1j S’31

S02 S12 S2j S32 K2j S’02 S’

12 S’2j S’

32 S03 S13 S3j S33 K3j S’

03 S’13 S’

3j S’33

S00 S10 S20 S30 S’

00 S’10 S’

20 S’30

S01 S11 S21 S31 S’

31 S’01 S’

11 S’21

S02 S12 S22 S32 S’02 S’

12 S’22 S’

32 S03 S13 S23 S33

S’13 S’

23 S’33 S’

03

S00 S10 S20 S30 S’

00 S’10 S’

20 S’30

S01 S11 Sij S31

S’01 S’

11 S’ij S’

31 S02 S12 S22 S32 S’

02 S’12 S’

22 S’32

S03 S13 S23 S33 S’03 S’

13 S’23 S’

33

S00 S10 S0j S30 S’

00 S’10 S’

20 S’30

S01 S11 S1j S31 S’

01 S’11 S’

ij S’31

S02 S12 S2j S32 S’02 S’

12 S’22 S’

32 S03 S13 S3j S33 S’

03 S’13 S’

23 S’33

S00

S10 S0j S30

K0j S’

00 S’10 S’

0j S’30

S01 S11 S1j S31 K1j

S’01 S’

11 S’1j S’

31

S02 S12 S2j S32 K2j S’02 S’

12 S’2j S’

32

S03 S13 S3j S33 K3j S’03 S’

13 S’3j S’

33

Fig 5: IMAES Encryption and decryption when S(state)is odd

K0

Add Round Key SP-Box

Sub Bytes Shift Rows Mix Columns Add Round Key

K1

Left rotate by 1

Left rotate by 3 Sub Bytes Shift Rows Mix Columns Add Round Key C(X) KNr-1

Sub Bytes Shift Rows Add Round Key

Cipher Text

Add Round Key KNr

Inv Shift Rows Inv Shift Bytes Add Round key Inv Mix Column

Right rotate by 1

Right rotate by 3

KNr-1

Inv SP-Box Inv Shift Rows Inv Sub Keys Add Round Key Inv Mix Column

KNr-2

C’(X)

Inv Shift Rows Inv Sub Bytes Add Round Key K0

Plain Text

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Plain Text S00 S10 S20 S30

S’00 S’

10 S’20 S’

30 S01 S11

Sij S31 S-Box S’

01 S’11 S’

ij S’31

S02 S12 S22 S32 S’02 S’

12 S’22 S’

32 S03 S13 S23 S33 S’

03 S’13 S’

23 S’33

S00 S10 S20 S30

S’00 S’

10 S’20 S’

30 S01 S11 S21 S31

S’11 S’

21 S’31 S’

01 S02

S12 S22 S32

S’22 S’

32 S’02 S’

12 S03 \S13 S23 S33 S’

03 S’13 S’

23 S’33

S00 S10 S0j S30

S’00 S’

10 S’20 S’

30 S01 S11

S1j S31 S’

01 S’11 S’

1j S’31

S02 S12 S2j S32 S’02 S’

12 S’2j S’

32 S03 S13 S3j S33 S’

03 S’13 S’

3j S’33

S00

S10 S0j S30

K0j

S’00 S’

10 S’0j S’

30 S01 S11 S1j

S31 K1j S’01 S’

11 S’1j S’

31 S02 S12 S2j S32 K2j S’

02 S’12 S’

2j S’32

S03 S13 S3j S33 K3j S’03 S’

13 S’3j S’

33

S00 S10 S20 S30 S’

00 S’10 S’

20 S’30

S01 S11 S21 S31

S’31 S’

01 S’11 S’

21 S02 S12 S22 S32

S’22 S’

32 S’02 S’

12 S03 S13 S23 S33 S’

03 S’13 S’

23 S’33

S00

S10 S20 S30

S’

00 S’10 S’

20 S’30

S01 S11 Sij S31

S’01 S’

11 S’1j S’

31 S02 S12 S22 S32 S’

02 S’12 S’

22 S’32

S03 S13 S23 S33 S’03 S’

13 S’23 S’

33

S00 S10 S0j S30

S’00 S’

10 S’20 S’

30 S01 S11 S1j

S31 S’01 S’

11 S’1j S’

31 S02 S12 S2j S32 S’

02 S’12 S’

22 S’32

S03 S13 S3j S33 S’03 S’

13 S’23 S’

33

S00 S10 S0j S30

K0j S’

00 S’10 S’

0j S’30

S01 S11 S1j S31 K1j S’01 S’

11 S’1j S’

31

S02 S12 S2j S32 K2j S’02 S’

12 S’2j S’

32 S03 S13 S3j S33 K3j S’

03 S’13 S’

3j S’33

Fig 6: IMAES Encryption and Decryption when S(state)is even

SP-Box

Inv SP-Box

Add Round Key

Sub Bytes Shift Rows Mix Columns Add Round Key

Sub Bytes Shift Rows Mix Columns Add Round Key

Sub Bytes Shift Rows Add Round Key

Inv Shift Rows Inv Shift Bytes Add Round key Inv Mix Column

Add Round Key

Inv Shift Rows Inv Sub Keys Add Round Key Inv Mix Column

K0

K1

KNr-1

KNr

KNr-1

KNr-2

K0

Right rotate by 2

Right rotate by 3

C(X)

Inv Shift Rows Inv Sub Bytes Add Round Key

X C’(X)

Left rotate by 3

Left rotate by 2

Cipher Text

Plain text

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3.3 Key Generation: In order to gain high security we use RC4 [22] key

generation algorithm to generate a key of 256 bit length with MAES. RC4 is a symmetric cipher and encrypts/ decrypts text byte-by-byte. The algorithm uses a mechanism to generate 8 bits pseudorandom numbers, which are used for encryption/ decryption. The algorithm is very simple. Its implementation is also very easy and consists of several simple machine operations, which makes the processing very fast. According to the journals, RC4 is 5 times faster than DES and 15 times faster than Triple-DES. On the other hand, the pseudorandom number generation is very close to one time pad, which makes the cipher very secure. RC4 generates a pseudorandom stream of bits (a key stream). As with any stream cipher, these can be used for encryption by combining it with the plaintext using bit-wise exclusive-or; decryption is performed the same way (since exclusive-or is a symmetric operation). (This is similar to the Vernam cipher except that generated pseudorandom bits, rather than a prepared stream, are used.) To generate the key stream, the cipher makes use of a secret internal state which consists of two parts:

1. A permutation of all 256 possible bytes (denoted "S" below).

2. Two 8-bit index-pointers (denoted "i" and "j"). The permutation is initialized with a variable length key,

typically between 40 and 256 bits, using the key-scheduling algorithm (KSA). Once this has been completed, the stream of bits is generated using the pseudo-random generation algorithm (PRGA).

3.2.1 The key-scheduling algorithm (KSA) The key-scheduling algorithm is used to initialize the

permutation in the array "S". "Key length" is defined as the number of bytes in the key and can be in the range 1 ≤ key length ≤ 256, typically between 5 and 16, corresponding to a key length of 40 – 128 bits. First, the array "S" is initialized to the identity permutation. S is then processed for 256 iterations in a similar way to the main PRGA, but also mixes in bytes of the key at the same time.

for i from 0 to 255 S[i] := i end for j := 0 for i from 0 to 255 j := (j + S[i] + key[i mod key length]) mod 256 swap values of S[i] and S[j] end for The pseudo-random generation algorithm (PRGA)

FIG 7: STAGES OF RC4

The lookup stage of RC4. The output byte is selected by

looking up the values of S(i) and S(j), adding them together modulo 256, and then looking up the sum in S; S(S(i) + S(j)) is used as a byte of the key stream, K. For as much iteration as are needed, the PRGA modifies the state and outputs a byte of the key stream. In each iteration, the PRGA increments i, adds the value of S pointed to by i to j, exchanges the values of S[i] and S[j], and then outputs the element of S at the location S[i] + S[j] (modulo 256). Each element of S is swapped with another element at least once every 256 iterations.

i := 0 j := 0 while Generating Output: i := (i + 1) mod 256 j := (j + S[i]) mod 256 swap values of S[i] and S[j] K := S[(S[i] + S[j]) mod 256] output K end while

4. MECHANISM OF THE PURPOSED ARCHITECTURE

4.1 Arithmetic coding: Arithmetic Coding [15] offers

extremely high coding efficiency and it provides little or no security as traditionally implemented. Arithmetic Coding is the most powerful technique for statically loss less encoding. The block diagram consists of a first coding and encryption step applied to the bits produced by encryption. At the Resaving side decryption and decoding of the image.

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Arithmetic coding encoder BEGIN Low_Val = 0.0; High_Val = 1.0; range = 1.0; while (byte_symbol != nTerminator) { get (byte_symbol); Low_Val = Low_Val + Symbol_Range * Symbol_Range_low (byte_symbol); High_Val = Low_Val + Symbol_Range Symbol_Range_high(byte_symbol); Symbol_Range = High_Val – Low_Val ; } Output a code so that Low_Val <= code < High_Val; END

Arithmetic coding decoder BEGIN get encoded value = value (code); Do { find a byte_symbol s so that Symbol_Range_low(s) <= value < Symbol_Range_high(s); Output s; High_Val = Symbol_Range_high(s); Symbol_Range = High_Val - Low_Val; Value = [value - Low_Val] / Symbol_Range; } Until byte_symbol s is a nTerminator END

4.2 IM AES (Improved Modified Advanced Encryption Standard)

We modify the AES [15] to be more efficient and secure way by adjusting the Shift Row Phase. MAES [1] provides better security and the modification are made in this by adjusting the shift row phase, but in order to reach higher performance and security we used IMAES.

Pseudo Code for Shift Row Shift Rows ( byte state [4, Nb] ) begin byte t[Nb] if state[0][0] odd numbers for r = 1 step 1, 3 x = r mod 4 if x = 0 step 0 to x + 1 for c = 0 step 1 to Nb – 1 t[c] = state[r, (c + x) mod Nb] end for for c = 0 step 1 to Nb – 1 state[r,c] = t[c] end for end for else for r = 2 step 2, 4 k = 0 x = r mod 4 if x = 0 step 0 to 3 for c = Nb - 1, c >= 0 , c -1 t[c] = state[x, (c + x) mod Nb , k + 1 end for for c = 0 , c < Nb , c + 1 state[x,c] = t[c] end for end for end

.

5. CONCLUSION:

The system offers compression and security and higher performance, image access in wireless and fixed covert communication networks. The Improved Modified Advanced Encryption Standard with Arithmetic Coding is more secure and reliable over real time applications . By using RC4 key generation in IMAES has facilitated towards the expansion of the key. The purposed cryptosystem provides better encryption and decryption results and reaches higher performance over real time application for security of images for transmission through covert low bandwidth channel.

6. FUTURE SCOPE:

Our proposed work output of encrypted images reveals that the technique presents higher performance, quit reliable and robust. But here techniques we have adopted for compression of image may changed by improved and reliable one so that they may deal besides floating point number such that space and time complexity may be reduced. Another thing that we have considered SP-Box in IMAES and their contents may be calculated via more effective and secure way besides product cipher. Finally, instead taking of Digital Image value from image buffer, this value may be calculated from Image directly.

Sangeeta Solanki,A K Vats,Shikha Maan, Int. J. Comp. Tech. Appl., Vol 2 (3),646-654

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Nomenclature IJCSNS International Journal of Computer Science

and Network S 226 security. IJCSE International Journal on Computer Science

and Engineering. WCE World Congress on Engineering. AC Arithmetic Coding AES Advanced Encryption Standard MAES Modified Advanced Encryption Standard IMAES Improved Modified Advanced Encryption

Standard

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Sangeeta Solanki,A K Vats,Shikha Maan, Int. J. Comp. Tech. Appl., Vol 2 (3),646-654

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