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A NOVEL STEGANOGRAPHY TECHNIQUE FOR GRAY AND COLORED IMAGES

Ankita Agarwal1, A. K. Vatsa2
  1. IMS Engineering College, Ghaziabad, UP, India.
  2. Shobhit University, Meerut, UP, India.
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Abstract

In today’s information age, information sharing and transfer has increased exponentially. The information vulnerable to unauthorised access and interception, while in storage or transmission. The threat of an intruder and Steganalysis accessing secret information for sharing information over an unsecure or covert communication channels are vulnerable to intruder attacks. Although, these techniques are often combined together to achieve higher levels of security but still there is a need of a highly secure system to transfer information over any communication media that minimizes the threat of intrusion. Therefore, to maintain secrecy either we need to make more robust steganography techniques against steganalysis or discover new and better techniques. In this paper, we propose a novel and more robust image steganography technique that embeds message into a cover media and hides its existence and can verify the reliability of the information being transmitted to the receiver. In order to hide secret data in cover-image it used the Image and Text files representation in Array, that takes the least and most significant-bit (LSB and MSB)-based approach and method of patching by contrasting process.

Keywords
Steganography techniques; Information Hiding; Information Security; (LSB and MSB)-based approach; Patching; PSNR.

INTRODUCTION
Generally, the information may be becomes secret by using two techniques that’s broadly used for security purposes [3], such as cryptography and steganography. The methods of cryptography render the data unintelligible to outsiders by various transformations, whereas the methods of steganography conceal the existence of messages. Steganography perform two principles, the first one is the capacity of hidden secret data, and another is the quality of the stego image. Steganography is a way for secret communication by using digital media to convey essential messages; it is the art and science of hiding communication. Thus it embeds hidden content in unremarkable cover media so as not to arouse an eavesdropper’s suspicion [27]. The most common thing in Steganography is to use images for steganography. This is called image steganography, in which the pixels of images are changed in order to hide the secret data so as not to be visible to users [10]. Also, watermarking used for privacy and copy right protection, [4] in field of data security
Images are the most popular cover objects used for steganography. The digital images many different image file formats exist, most of them for specific applications. For these different image file formats, different steganographic algorithms exist. This numeric representation forms a grid and the individual points are referred to as pixels [29]. Most images on the internet consists of a rectangular map of the image‘s pixels (represented as bits). Not surprisingly the larger amount of colors that can be displayed, the larger the file size.
The word steganography comes from the Greek Steganos, which means covered or secret i.e., Steganography means literally covered writing. It is the method of hiding information such that its presence cannot be detected [1], such that an adversary is supposed to be unable to distinguish between cover and stego images. A secret message is embedded in such a manner that the existence of the information is hidden and to establish a secured communication in a completely undetectable manner [2]. In the case of images, the carrier is referred to as the cover image, while after embedding secret data into it; the stego image can be obtained.
Different types of security techniques are used for providing security are as follows:
Spread Spectrum techniques, ables to hides data are spread throughout the cover-image making it harder to detect [31]. Spread spectrum communication can be defined as the process of spreading the bandwidth of a narrowband signal across a wide band of frequencies [32]. This can be accomplished by adjusting the narrowband waveform with a wideband waveform, such as white noise. After spreading, the energy of the narrowband signal in any one frequency band is low and therefore difficult to detect. In spread spectrum image steganography, the message is embedded in noise and then combined with the cover image to produce the stego image. Since the power of the embedded signal is much lower than the power of the cover image, the embedded image is not perceptible to the human eye or by computer analysis without access to the original image.
JPEG Steganography is one which hidden in the redundant bits of an object and since redundant bits are left out when using JPEG it was feared that the hidden message would be destroyed. However, properties of the compression algorithm have been exploited in order to develop a steganographic algorithm for JPEGs. One of these properties of JPEG is exploited to make the changes to the image invisible to the human eye. During the DCT transformation phase of the compression algorithm, rounding errors occur in the coefficient data that are not noticeable [30].
File Structure Based Steganographic Methods Different image file formats have different header file structures. The secret information can be hidden not only in the data values, e.g., pixels, palette, DCT coefficients, but also in the header structure or at the end of a file [28]. For instance, Invisible Secrets and Steganozorus hide data with the comment fields in the header of JPEG images. Camouflage, JPEGX, PGE10 and PGE20 add data at the end of a JPEG image.
Palette based Steganogarphy[7] is one in GIF images are indexed images where the colors used in the image are stored in a palette, sometimes referred to as a color lookup table. Each pixel is represented as a single byte and the pixel data is an index to the color palette [30]. The colors of the palette are typically ordered from the most used color to the least used colors to reduce lookup time. GIF images can also be used for LSB steganography, although extra care should be taken. The problem with the palette approach used with GIF images is that if one changes the least significant bit of a pixel, it can result in a completely different color since the index to the color palette is changed.
The information vulnerable to unauthorised access and interception, while in storage or transmission. The threat of an intruder and Steganalysis accessing secret information for sharing information over an unsecure or covert communication channels are vulnerable to intruder attacks. Although, these techniques are often combined together to achieve higher levels of security but still there is a need of a highly secure system to transfer information over any communication media that minimizes the threat of intrusion. Therefore, to maintain secrecy either we need to make more robust steganography techniques against steganalysis or discover new and better techniques.
This paper organized in Sections. Firstly we describe the introduction of Security of data, Steganography, Images, and other security Techniques under the heads of Introduction in Section-I. Subsequently we have gone through the literature review and found problems and solutions in several papers. All this we have mentioned under heads of Backgrounds in Section-II. In Section-III, the proposed architecture and mechanism described in detail. Finally, this paper concluded and mentions its further enhancements under future scope in Section – IV and Section-V respectively. All used references used during writing of this paper are mention in Section –VI under head of references.

BACKGROUNDS
A novel steganographic method [5] based on JPEG [19]. It takes advantage of the quantization error resulting from processing the JPEG-compressed image [21, 22] with two different scaling factors. One of the scaling factors is used to control the bit rate of the stego image while the other is used to guarantee the quality of the stego image. Experimental results show that this steganographic method provides high information hiding capacity and successfully control the compression ratio and distortion of the stego image.
A color image steganography method based on the module substitutions [6] is proposed. In accordance with the base-value of the blocks, a variety of secret bits is embedded to a RGB trichromatic system by three types of module substitutions [23]. More specifically, to alleviate further color distortion and obtain a larger hidden capacity, the R-, G- and B-component is encoded by Mod u, Mod u-v, and Mod u-v-w substitution, respectively. Experiments show that both PSNR and hiding rate generated by this method are better than those generated by the reported schemes. In addition, the resulting perceptual quality is good.
A new steganography technique [7] for palette based images [26]. Secret message is encrypted using public key cryptography before hiding. The bits of encrypted message are hidden inside the stretched palette of image. There are several limitations. The process of stretching palette by adding new colors is an overhead and takes some time. However, as the time is not a critical factor for this type of work, and it is very small, not much attention is drawn. Another limitation of the method is vulnerability to alteration of the image. Compression of the image is also resulted in destroying the hidden message. If the image is distorted & compressed, the hidden message cannot be extracted.
A least significant bit [8] (4LSB) is a substitution method [12, 13]. The 4LSB method is implemented for color bitmap images (24 bit and 8 bit i.e. 256 color palette images) and wave files as the carrier media. When applying 4LSB techniques to each bytes of a 8-bit image, one bit can be encoded to each pixel. Any changes in the pixel bits are indiscernible to the human eye. By using this algorithm, one can hide its file of any format in an image and audio file. He can then send the image via e-mail attachment or post it on the web site and anyone with knowledge that it contains secret information, and who is in possession of the encryption password, can open the file, extract the secret information and decrypt it.
An image steganograph [9] gives high capacity and good security. Based on local complexity of a cover image, varying-depth embedding is used to improve the imperceptibility and to decrease distortions in it. Experimental results show that the steganographic technique provides higher capacity and be resistant to several well-known steganalytic methods.
New image steganography scheme which is a kind of spatial domain technique [10]. In order to hide secret data in cover-image, author used the Just Noticeable Difference (JND) technique and method of Contrast Sensitivity Function (CSF) [24, 25]. This is an edge-detection which uses part information of each pixel-value. In order to have better imperceptibility, a mathematical method 2k correction is proposed. 2k correction corrects each pixel-value as 2k. This means if k-bits are embedded in a pixel value, the method adds or subtracts 2k to each pixel-value and finally the corrected pixel value becomes closer to the original-pixel. Hence, the secret data in the stego-pixel is not changed. This scheme embeds more data than previous schemes and shows better imperceptibility.
Secure Image Steganography based on Randomized Sequence of Cipher Bits [16] provides a technique based on seed ranking. In order to hide image it uses single image for suitability based on seed ranking. It does not require the user to select the multiple images for suitability. Steganography when combined with randomized sequence of cipher bits provides a better means of secret communication between two parties. This application is based on seed ranking of an image.

PROPOSED STEGANOGRAPHY TECHNIQUE

Architecture of Proposed Steganography Technique:

Sender’s Prospects:
image
Figure-1 shows the sender’s prospect of Steganography Technique in which sender Input an image called cover image or original image of any file format(JPEG, BMP,DIP etc ) in which he wants to hide the secret message and text file containing secret data has to be embedded in an image file. Image containing the secret data is called stego image. Next phase is to select the stego key for encoding. In Embedding process data is hidden by using Exchange component alteration technique in which pixels have been replaced by key and secret message. Firstly key is converted into binary form and its binary form is filled in the first component of first pixels. After then, secret message is converted into binary form and its binary form is filled in first component of next pixels. For more security of stego image patching technique is applied by contrasting process. Finally, the verification will be done by parameters PSNR and MSE for stego image of same format and size that gives better result in form of than existing techniques.

Receiver’s Prospects:
image
Figure-2 shows the receiver’s prospect of Steganography Technique in which the sender sends a stego-image to the receiver or legitimate user. The legitimate user having the stego key to extract secret data from stego image. The legitimate user must have the same key with which the image is embedded. On Stego image Extracting process is applied by using Patching techniques and Exchange Alteration techniques. Finally we get the Secret Data which is embedded.

Mechanism of Proposed Steganography Technique:

Sender’s Prospects:
Phase - 1: Original Image and Text File: The original image is of any file format having 24 bits per pixel. Due to low computational complexity, it can be applied to very small images of (24 x 24) pixels as well as large images of (512 X 512) pixels. This technique can encode gray scale images as well as colored images directly, with R-G-B levels. After selecting image file, text file is selected which contains secret data.
Phase - 2: Stego Key is a secret variable key that shares sender and receiver. If the key is valid, then only receiver can decode image and retrieve secret data.
Phase - 3: Embedment of Data and Stego Key in Image using Proposed Exchange Component Alteration and Patching Technique:
Step (a): The original image is represented in Image buffer as f (i, j) that contains M x N pixels and a reconstructed image F (i, j) where F is reconstructed by encoding the f (i, j). Extract all the pixels in the given image f (i, j) and store it in the array called Pixel-Array p (i, j).
Step (b): Extract all the characters in the given text file and store it in the array called Character- Array c(i, j).
Step (c): Extract all the characters from the Stego key and store it in the array called Key- Array k(i, j).
Step (d): Exchange first pixel with last pixel of each row of Pixel-Array p (i, j) (i.e LSB ↔ MSB).
Step (e): Replace first pixel of each row of Pixel-array p(i, j) with first pixel of each row of Key- Array k(i, j). If there are more no. of character available in Key- Array, then place rest of remaining character in the next component of pixels array, otherwise follow Step (f).
Step (f): The terminating symbol 0 indicates the end of the key in Key- Array k (i, j).
Step (g): Place characters of Character- Array c(i,j) in each first component (blue channel) of next pixels by replacing it.
Step (h): Repeat step (f) till all the characters of character array c(i,j) has been embedded.
Step (i): Again place some terminating symbol 0 in end of the Character- Array c(i,j) to indicate end of data.
Step (j): A pseudorandom generator is used to select two fields of the image (or patches), patch A and patch B.
Step (k): All the pixels in patch A is lightened while the pixels in patch B is darkened. In other words, the intensities of the pixels in the patch A are increased by a constant value, while the pixels of the other patch B are decreased with the same constant value. For each pair, let d be the difference between intensities of two pixels. Encode a bit of information in to the pair.
Step (l): Let d<0 represents 0 and d>0 represents 1. If the pixels are in the wrong order, switch them. If d happens to be greater than a predefined threshold or if equal to 0, discard the pair and move on to next pair.
Step (m): Resultant image will hide all the characters that we input. Data is embedded using above algorithm and stego image is produced and sent to the receiver or legitimate user.
Step (n): Error metrics are computed on the luminance signal only so the pixel values f (i, j) range between black (0) and white (255). Firstly, the mean squared error (MSE) of the reconstructed image is computed as follows:
image

Receiver’s Prospects:
Phase - 1: Stego Image: The sender sends a stego image to the receiver or legitimate user. The legitimate user is having the stego key to decode secret data from stego image.
Phase - 2: Stego Key after receiving stego image by receiver or legitimate user, the legitimate user must have the same shared key with which the image is encoded.
Phase - 3: Extracting of Stego Image using Proposed Exchange Component Alteration and Patching Technique:
Decoding algorithm of exchange component alteration and patching technique includes following steps:
Step (a): All the pixels in patch A is darkened while the pixel in patch B is lightened to original. In other words the intensities of the pixels in the one patch are decreased by a constant value, while the pixels of the other patch are increased with the same constant value.
Step (b): Consider three arrays. Character-Array c(i, j), Key-Array k(i,j) and Pixel-Array p(i,j).
Step (c): Extract all the pixels in the given image f (i, j) and store it in the array called Pixel-Array p (i, j).
Step (d): Now, start scanning pixels from first pixel and extract key characters from first (blue) component of the pixels and place it in Key-Array k(i,j). Follow Step 3 till we get terminating symbol, otherwise follow step (e).
Step (e): If this extracted key matches with the key entered by the receiver, then follow Step 5, otherwise terminate the program by displaying message ―Key is not matching.
Step (f): If the key is valid, then again start scanning next pixels and extract secret message characters from first (blue) component of next pixels and place it in Character Array c(i,j). Follow Step (f) till we get terminating symbol, otherwise follow step 6.
Step (g) : Exchange last pixel with first pixel of each row of Pixel-Array p (i, j) (i.e MSB ↔ LSB).
Step (h): Extract secret message from Character-Array c(i,j). Thus in this way secret message is decoded and received by receiver.

CONCLUSION
It was appeared that [10,11,13,14] uses 4LSB techniques which was not able to store tremendous information and even not more secure, also Palette-based image techniques[17, 18] may look suspicious i.e thus detectable. This paper proposed a novel image steganography technique that work on 8LSB techniques and could embed more data than related previous steganography schemes by hiding secret data in cover-image. It used the Image and Text files representation in Array, that takes the least and most significant-bit (LSB and MSB)-based approach and method of patching by contrasting process. Not only does this scheme hides more data and has better imperceptibility than others available techniques but also has improves quality of stego image and gives better results than existing one.

FUTURE ASPECTS
The proposed steganography technique for gray and colored images will provide effective security for images with efficient manner but this work may be further improved for other types of images like TIFF, JPEG2000 etc as this images has the aspect of the slightly contrary i.e having greater resolution to other application of proposed method. Therefore, future work includes the search for the plan which is not contrary to the other. Video files can also be used to transmit data, however the time consumption will increase in this case.

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