Investigation of Digital Image Steganography:A … of Digital Image Steganography:A Survey . Chetna ... carries a hidden text message. ... Fig.1 illustrates the process of steganography

Investigation of Digital Image Steganography:A Survey

Chetna Mehto

M.tech scholar

Department of CSE TIT, Bhopal (India)

[email protected]

Rachana Kamble

Asst. Professor


[email protected]

Dr. Bhupesh Gour

Professor


[email protected]

Abstract

With the exponential growth in Internet usage, demand for

effective information security techniques is increasing day by

day. Digital image steganography is one of those techniques

that are used for effective secret communications. In this

technique, secret communication is achieved by embedding a

message into a cover image and generating a stego-image that

carries a hidden text message. This paper provides the details

of digital image steganography and presents a brief review of

various steganography techniques proposed recently by

various researchers around the globe. We propose a

technique that mingles up the hash code and ciphertext, and

embeds both of them in a single image so that it becomes very

hard for an attacker to separate them or replace. The

proposed algorithm will benefit the sender and receiver, as

they do not need to send two different files. On the other hand,

it will be much more difficult for the attacker to break the

proposed algorithm by unauthorized user.

1. Introduction When data is exchanged in an open network, the security of

information being exchanged becomes a major concern. Since

internet is a worldwide collection of loosely connected

networks having no geographical, national or international

boundaries hence there is even more risk associated with the

security of information that we put on there.

The essence of steganography lies in storing the secret

information inside an image file in such way that no one else

except the sender of the information and the intended receiver

can suspect about the existence of any sort of information

behind it. Although aim of both steganography and

cryptography is to hide the secret information but it is

achieved through entirely different ways in both the

techniques. Good imperceptibility and sufficient data capacity

are the two properties, which an effective steganography

technique must possess[1].

Section 2 presents the basic process of steganography named

by how steganography works, section 3 presents the basic

types of steganography along with their merits and demerits.

Section 4 discusses about stegnalysis, Section 5 presents the

image steganography tools. Section 6 presents technique used,

section 7 a brief discussion on related works section 8 presents

proposed work, and finally section 9 concludes the paper lastly section 10 represent references.

2. How Steganography Works Image Steganography means to conceal messages inside an

image where pixel intensities are used to hide the information.

The secret text message and a cover image are supplied as

input to the steganography algorithm, which writes the given

text message inside the cover image and as a result, it produces

the stego image. The secret message is written inside the image

in such a way that the quality of image does not change

significantly and thus no one can suspect that the image carries some secret information.

Fig. 1. Basic process of coding and decoding in steganography

Fig.1 illustrates the process of steganography where secret text

message is embedded inside the cover image to produce a

stego image. The receiver applies reverse algorithm to recover

the hidden text message from stego image. Many people think

MESSAGE

EMBEDDING

ALGORITHM

STEGO IMAGE

REVERSE ALGORITHM

RECOVERED MESSAGE

COVER IMAGE

Chetna Mehto et al, Int.J.Computer Technology & Applications,Vol 5 (5),1711-1717

IJCTA | Sept-Oct 2014 Available [email protected]

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that cryptography and steganography are nearly same thing

but there is a huge difference between them. Cryptography

refers to converting the information in such a form that the

existence of the encrypted message is visible to the world but

no one can interpret the message except the sender and

receiver, whereas steganography deals in hiding messages

such that no one, except the sender and receiver knows that

the message even exists. Thus steganography prevents

unwanted attention of attackers towards the hidden message.

Fig.2(a) and (b) show the advantage of using digital

steganography over cryptography. Communication through

steganography increases the level of confidentiality and

privacy in electronic communication by transferring

information in an invisible form.

(a) Cryptography

(b) Steganography

Fig. 2. Cryptography and steganography

3. Types Of Steganography a) Spatial Domain Methods: It directly changes some bits in

the pixel values of the cover image while hiding the data.

Least significant bit (LSB)-based steganography is one

such simplest techniques that hides secret message in the

LSBs of pixel values without introducing much human

perceptible distortions [2]. Embedding of message bits can

be done either sequentially or randomly by using bit

insertion or noise manipulation of cover image. LSB

replacement, LSB matching, Matrix embedding and Pixel

value differencing techniques fall under spatial domain.

b) Transform Domain Technique: Various algorithms and

transformations are applied on cover image in order to hide

information behind it. These techniques hide information

in those areas of cover image that are less exposed to

compression, cropping, and other image processing

operations. Discrete Fourier transformation technique

(DFT), Discrete cosine transformation technique (DCT),

and Discrete Wavelet transformation technique (DWT) fall

under transform domain. Smooth homogeneous areas in

images must be avoided whereas chaotic with natural

redundant noise background and salient rigid edges should

be targeted for embedding the message.

c) Distortion Techniques: Distortion techniques require

knowledge of the original cover image for embedding the

message into cover image. The decoder functions are

applied in order to check the dissimilarity between original

cover image and the stego image for restoring the secret

text message. The necessity of sending cover image along

with cover image delimits the benefits of this technique.

d) Masking and Filtering: This approach hides the

information by marking an image in the same manner as

paper watermark does. These techniques embed

information in more significant areas than simply hiding it

into the noise level. These techniques are applicable only

to gray scale images and are restricted only to 24 bits.

TABLE I. MERITS AND DEMERITS OF VARIOUS STEGANOGRAPHY

Spatial

Domain

Merit

Small probability of degradation in

original image.

High hiding capacity

Demerit

Data may be lost when image is manipulated

It is easy to destroy data by simple

attacks

Transform

Domain

Merit

Much stronger technique

Data do not lost easily when image is

manipulated

Demerit

Low hiding capacity

Cannot resist attacks based on multiple

image processing techniques

Distortion

Domain

Merit

Message is encoded at pseudo-randomly

chosen pixels

Intended receiver can easily detect any

type of tampering

Demerit Requires knowledge about cover image

while decoding

Masking &

Filtering

Merit It is more robust than LSB replacement

Demerit It is applicable only to 24 bits gray scale

images

4. Steganalysis Steganalysis is the science of attacking steganography in order

to extract the hidden text message. It is achieved by applying

various image processing techniques such as image filtering,

Encryption

Process

Plaintext

Plaintext

Decryption

Process

Encryption Key Decryption Key

Ciphertext

Encryption

Process

Plaintext

Plaintext

Decryption

Process

Encryption Key Decryption Key

Ciphertext

Stego- Image

Stego Key

Message Cover image

Embedding

algorithm

Secret Key

Encryption

Algorithm



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cropping, rotating, translating etc. [3] or more deliberately by

coding a program that examines the stego image structure and

measures its statistical properties e.g., histograms and

correlations between pixels. In order to resist various types of

attacks, following security measures should be taken to

achieve effective stenganography:

a) For eliminating the attack of comparing the original image

file with stego image, where a very simple kind of

steganalysis is essential, one should create a cover image

and destroy it after generating the stego image. Cover

images from Internet are not advisable as an attacker might

utilize them for decoding the stego image.

b) Any alteration up to the 5th LSBs of a given pixel yields a

dramatic change in its intensity. To avoid any Human

visual perceptual attack, the generated stego image must

not have visual artifacts. c) Smooth homogeneous areas must be avoided whereas

chaotic with natural redundant noise background and

salient rigid edges should be targeted for embedding the

message. 5. Image Steganography Tools We analyzed 14 open source and 34 commercial

steganographic tools, which are mentioned in Table.2. It was

observed that JPEG and BMP are good choice to be used as

cover image for open source tools as 9 of these tools support

these image formats. The next popular format is GIF, where

Mandlesteg, GifShuffle and F5 are useful. Wnstorm and dc-

Steganograph embeds information with PCX files on the other

hand PGMStealth and OutGuess uses PGM and PNG formats

respectively. Most of these tools embed information using

spatial domain techniques i.e. by changing or replacing pixel

values, whereas F5, OutGuess and dc-Steganograph works in transform domain.

TABLE II. IMAGE STEGANOGRAPHIC TOOLS

Image stegano-

graphic tools JPEG BMP Other

Embeddin

g

Approach

Prod-

uction

Blindside Yes SDS Yes

Camera Shy Yes SDS Yes

dc-

Steganography PCX TDS

F5 Yes Yes GIF TDS Yes

Gif Shuffle GIF

Change

order of the

color map

Yes

Hide 4PGP Yes SDS Yes

JP Hide & Seek Yes SDS Yes

J steg J peg Yes SDS Yes

Mandelsteg GIF SDS Yes

Out Guess Yes PNG TDS Yes

PGM Stealth PGM Yes

Steghide Yes SDS Yes

wb Stego Yes SDS Yes

Wn Strom PCX Yes

6. Techniques used In this research we have used Advanced Encryption Standard

(AES) technique for encryption and decryption of text

message. We have used SHA-512 for calculating the hash

value for ensuring the integrity of hidden message.

a) Advanced Encryption Standard (AES)

It is a block cipher technique proposed by Joan Daemen and

Vincent Rijmen. This algorithm is very flexible in terms of

combination of data and key size, which can be either of 128,

192, or 256 bits. Conversely, AES requires that the plaintext

Expand Key

W[40,43]

Key Key

y

W [0,3]

W[4,7]

WKey

W [36, 39]

Key

Plaintext

Add Round Key

Subsitute bytes

Shift Rows

Mix Columns

Add Round Key

Subsitute bytes

Shift Rows

Add Round Key

Ciphertext

Subsitute byte

Shift Rows

Mix Columns

Add Round Key

Plaintext

R

ound 1

Round 9

Round 1

0

Round 1

0

Round 9

R

ound 1

Add Round Key

Inverse Substitute Bytes

Inverse Shift Rows

Add Round Key

Ciphertext

Inverse Mix Columns

Add Round Key


Inverse Shift Rows

Inverse Mix Columns

Add Round Key


Inverse Shift Rows



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must be 128 bits long, which can further be separated into four

operational blocks. These blocks operate on an array made up

of bytes arranged in a 4×4 matrix known as state. During

encryption, data passes through N number of rounds (N = 10,

12, 14). These rounds perform following transformations on the data:

Fig 3 AES Encryption Algorithm

Sub byte Transformation: This includes a non linear byte

substitution using a substitution table called s-box, which is

constructed by employing affine transformations and multiplicative inverse.

Shift rows transformation: It is an extremely simple yet quite

powerful byte transposition method where the bytes in last 3

rows of a state are shifted cyclically and offset of the left shift

is varied by 1 to 3 bytes.

Mix columns transformation: It It is similar to applying

multiplication of different columns in a matrix. Every column

vector is multiplied with the fixed matrix. It should be noted

that the bytes are calculated as polynomials, instead of

numbers.

Add round key transformation: It is a simple XOR operation

of state with the round key. This transformation has its own

inverse.

Inverse Substitute Bytes: It is the exact reverse process of

substituting byte transformation, where the inverse s-box

transformation is applied over every byte of the state. It can be

obtained by calculating inverse of the affine transformation

followed by multiplicative inverse.

Inverse Shift rows: It is an inverse operation of the shift rows

transformation. The first row of any state array remains

unaltered, and the bytes on second, third and forth rows are

shifted cyclically by one, two and three bytes respectively

towards right.

Inverse Mix columns: Each column in the state array is

considered as a polynomial. After multiplying modulo x4+1

with a fixed polynomial, the corresponding column of output state is obtained.

b) Secure Hash Algorithm-512(SHA-512)

SHA512 is a cryptographic hash functions developed by U.S.

National Security Agency (NSA) in 2001. Cryptographic hash

functions are sort of mathematical operations that operate on

digital data. When the hash value of received message is

compared with that of original message, the authenticity of the

data can be determined. For example calculating a hash over

the downloaded software and analyzing the result by

comparing it with the hash result published by the developer

one can decide the genuineness of that software and weather it

is safe to run or not. Besides this, it is about impractical for an attacker to reverse engineer and recreate the data.

Fig.4 Generation of SHA-512 message digest

The SHA-512 compression function shown in Fig.4, is the

heart of this algorithm. It processes the message in 1024-bit

(128-word) blocks using a module that consists of 80 rounds.

Each round takes 512-bit buffer value as input, and updates the

contents of buffer. Each round makes use of a 64-bit value

derived using a message schedule from the current 1024-bit

block being processed. Each round makes use of an additive

constant based on the fractional parts of the cube roots of first

eighty prime numbers. The output of eightieth round is

supplied as input to the first round to produce final hash value

for a message block. The resulting block forms the input for

next iteration of compression function.

7. Related Work Hemalatha et al. [4] proposed an image steganography

technique to hide multiple secret images and keys in color

cover image using Integer Wavelet Transform (IWT). Authors

claim that there is no visual difference between the

stegoimage and cover image, also a very good PSNR (Peak

Signal to Noise Ratio) values obtains for both stego images.

Shamim Ahmed Laskar et al. [5] proposed a high capacity

data embedding approach by the combination of

Steganography and cryptography. In this process, a message is

first encrypted using transposition cipher method and then the

+ = word by word addition (mod 264)

1024

bits

1024

bits

1024

bits

IV=

H0

512 H1 H2

1024 1024

HN=

Hash

Code

1024

F + F + F +

128

bits

M1 M2

Message

Nx1024 bits

L bits

100..0

MN

L



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encrypted message is embedded inside an image using LSB

insertion method. The authors claim that combination of these

two methods enhances the security of the data embedded, and

this combinational methodology satisfies the requirements

such as capacity, security and robustness for secure data

transmission over an open channel.

Usha B.A. et al. [6] proposed a neural network based

technique for steganography. The amount of data that can be

hidden inside the cover image chosen depends on the

properties of the image like number of noisy pixels. The

neural network based image steganography ensures that

quality and size of the image remains same after embedding

the data.

Current trend in steganalysis generally suggests two extreme

approaches (a) little or no statistical assumption about the

image under investigation, where statistics are learned using a

large database of training image and (b) a parametric model is

assumed for the image and its statistics are computed for

steganalysis detection. P. T. Anitha et al. [4] developed a new

hybrid approach, which comprises of neural network and S-

DES encryption scheme which is used to detect the stego

content in corporate mails. For this purpose, authors

implemented the combination of compression, encryption, and

steganography to enhance the security of the data sent and

steganalysis methods.

Inderjeet Kaur et al. [8] proposed a transform domain based

technique with the aid of segmentation and watermarking

(TDSSW) that combines steganography and watermarking to

provide copyright protection to the information being

transmitted secretly. The carrier (cover image) is segmentated

into 8×8 blocks and Discrete Cosine Transform (DCT) is

applied on each segment. The MSB of payload is embedded

into DCT coefficients of the cover image based on the values

of DCT coefficients to obtain the stego image. Authors claim

that this technique is capable to improve peak signal to noise

ratio.

In [9], authors Atallah et al. proposed a method that hides the

secret message based on searching about the identical bits

between the secret messages and image pixels values. They

claimed that this technique works better as compared to LSB.

They also claim that the proposed technique is efficient, simple

and fast it robust to attack and improve the image quality,

which obtains an accuracy ratio of 83%.

Pragya Agarwal et al. [10] proposed a scheme under which, a

SHA-1 hash code is generated from original text message,

which is sent to the receiver through a secure channel. The

receiver can authenticate the received hash to ensure the

integrity of the original message. The message is sent to receiver by hiding it into an image using image steganography.

Soumik Das et al. [11] proposed a technique in which, a 32-bit

secret key is provided by encrypter, which is applied on the

text with a hash function to generate a pseudo byte stream. This

stream is written directly to image pixels and thus the text

becomes physical property of encrypted image. An intruder

cannot succeed if he tries to perform the extraction of text with

a wrong secret key. The extraction of the text is blind i.e. except the secret key nothing is required for text decryption.

In [12], Rinu Tresa et al. came up with a technique that

combines both steganography and cryptography so that

attacker doesn’t know about the existence of message and the

message itself is encrypted to ensure more security. The textual

data entered by the user is encrypted using AES algorithm.

After encryption, the encrypted data is stored in the colour

image by using a hash based algorithm. This technique does

not corrupt images quality in any form. Its major advantage is

that it is suitable for almost all image formats such as

JPEG/JPG, BMP, TIFF and GIFF.

Kritika Singla et al. [13] proposed a scheme that achieves high

embedding capacity and enhances the quality of the encoded

image. It first detects the edges in the image by well known

canny edge method and then the hash sort is employed to

embed the text data in to the edges of the color image. The

hash function provides a secure and fast approach for image

steganography.

Seongho Cho et al.[14] proposed A block-based image

steganalysis system and conducted extensive performance

evaluation of block-based image steganalysis. They studied the

performance of block-based steganalysis by varying different

parameters, including block number, block size, effects of

block overlapping, class number of block, classifier choice and

the decision fusion scheme. It was practically seen that the

performance of block-based image steganalysis is not much

sensitive to the decision fusion approach but more responsive to classifier choice.

Firas A. Jasim[15] proposed a novel method for steganography

which is based on FMM method The stego images obtained

has been tested using PSNR value. Author analysed the PSNR

value and proved that the stego images are having high PSNR,

the ST-FMM novel steganography algorithm is very effective

in hiding the information inside an image.

Dr. Ekta Walia et al.[16] proposed LSB & DCT based

Steganography to calculated the PSNR ratio. Result reveal that

PSNR ratio for DCT based steganography scheme is higher

than LSB based steganography scheme for various types of

images. They have also shown that as DCT based

steganography scheme has the minimum distortion of image

quality, so DCT is preferred over LSB steganography scheme

inspite the fact that amount of secret data that can be hidden

using this technique is quite small.

Deepesh Rawat et al. [17] proposed a technique for hiding text

information in color images. They improved the well known

LSB method, they chose Bitmap and JPEG image formats, and

calculated PSNR, MSE (Mean Squared Error) and histogram.

Results showed that on increasing the size of cover image, a

large amount of secret information can be embedded. It is

because only a single bit of every pixel gets changed, and only



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minor changes in histogram are observed hence stego image is visually identically same as was the original cover-image.

8. Proposed Work In the work proposed by Soumik Das et al. [11], it was not so

hard for an attacker to generate a ciphertext and hash code of a

new plaintext and replace them both. The entire problem was

due to the reason that attacker can have access to both

ciphertext and the hash code separately. We propose a solution

to this problem by mingling up the hash code and ciphertext,

and then embedding them in a single image so that it becomes

very hard for an attacker to separate them and replace. On the

one hand, proposed algorithm will benefit the sender and

receiver as they will not need to send two different files.

Whereas on the other hand, it will be much more difficult for

the attacker to break the algorithm as he cannot separate the

ciphertext and hash code. The proposed technique makes use

of the AES algorithm. The AES is more resistant towards

differential and linear cryptanalysis as a bit flip at some point

quickly propagates to the complete internal state AES [18] due to the fact that:

AES is highly desirable for large block size inputs.

AES is highly efficient, secure with high speed of encryption & decryption processes.

AES uses varying Key Length of 128 bits, 192 bits,

256 bits for each 128 bits input text block. Input is

processed in form of multiples of 128 bit blocks. At a time, each 128 bits block are feeds as a input.

AES uses four stages for each round except last round.

In the last round it uses only three stages to produce

128 bit encrypted cipher text.

Four stages are: Substitute Bytes, Shift Rows, Mix

Columns, and Add Round Keys. Last round uses three stages excluding Mix column stages.

The proposed work also uses SHA-512, which is a variant of

SHA-256 and is more cost effective to be computed as

compared to SHA-256 over a given size of data. The SHA-512

algorithm delivers a 50% performance improvement over SHA-

256 [19]. It is essentially a 512-bit block cipher algorithm,

which encrypts the intermediate hash value using the message

block. The key for the calculation of hash as SHA-512 has

following strengths:

Input message divided into multiple of 1024 bits of

block. Each 1024 further divides in 16 sub-blocks of 64 bits of each word size for proceeds.

Each round has 20 stages, and four such rounds are

carried out for performing 80 iterations to produce 512

bits of message digest as output.

SHA-512 uses eight 64 bits buffer’s to hold intermediate and final results.

The algorithm for the proposed steganography technique can be summarized as follow:

2) Initially, the secret information is provided as input, which

has to be sent over a vulnerable network.

3) AES encryption is applied over this information and the

result obtained is so called ciphertext.

4) Simultaneously SHA-512 is also applied on secret

information which produces the message digest (MD).

5) After this, a mixing algorithm is applied for mixing the

ciphertext and MD to produce a mingled code.

6) The resultant mingled code is then embedded into a cover

image and sent to the receiver end.

7) On receiving this stego image, the receiver dig up the

mingled code from the stego image and applies reverse

mix up algorithm to separate the cipher text and MD code.

8) AES decryption takes the ciphertext as input and produces

original secret message as output.

9) SHA-512 is applied on retrieved secret message to obtain

the new message digest (MD’).

10) Receiver compares the MD value with MD’, if the values

are equal then the received message is intact and has not

been altered.

9. Scope of the survey This paper briefly describes the concept of steganography and

its major types. Since each technique comes with its own weak

points hence the merits and demerits of available techniques

were also elaborated. The steganographic system leaves unique

patterns on the cover images and these patterns feats the

steganalyst. Hence the properties that an effective

steganography algorithm should possess are also elaborated in

this paper. After a long tenure of research in this area, there is

still a requirement for a robust and efficient steganography

technique that can overcome the demerits of existing

techniques.

REFERENCES

[1] Sandeep et al., “A Review on the Various Recent

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[3] Abbas Cheddad, “Digital Image Steganography: Survey and Analysis of Current Methods,” Elsevier, Signal Processing,

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[4] Hemalatha S et al. “A Secure and High Capacity Image

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[9] Atallah M. Al-Shatnawi, “A New Method in Image

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Investigation of Digital Image Steganography:A … of Digital Image Steganography:A Survey . Chetna ... carries a hidden text message. ... Fig.1 illustrates the process of steganography