This study projects a unique means of steganography incorporating two diverse plots for images viz., compression and encryption. Being indispensable for the sake of e-world, where images are numerously involved information security has caught attention of many. In this heterogeneous distributed computing world data are transferred accurately and faster. Many transmission mediums are available to send the data through internet. The main concern of the data transfer is to secure the data without any unauthorized access. To have a secured data transfer steganography and cryptography methods are involved. Cryptography scrambles the data whereas steganography conceals the data transfer. In this proposed method secret text is compressed using Shannon fano method and then encrypted using rail fence cipher followed by ceaser cipher to improve the security. Mean Squared Error (MSE) and Peak Signal-to-Noise Ratio (PSNR) are calculated and analysis is done. K-bit embedding is employed in this study to put the secret out of sight. This study pledges security, embedding capability and imperceptibility possessing high hardiness to security threats.
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In the current fashions of the world, everybody transfers data from one to another end in this world through internet. One of the important anxieties of the internet is the security hazard. To prevent the confidential data from malicious user various security methods like cryptography (Salem et al., 2011; Schneier, 2007), steganography and watermarking (Abdulfetah et al., 2010; Zeki et al., 2011) are developed (Stefan and Fabin, 2000; Rajagopalan et al., 2012). Cryptography encrypts the covert data thus generates cipher text and then transmits to the destination with unfamiliar key. Steganography goes one step further by disguising it in any communication media (Bender et al., 1996) like text (Xiang et al., 2011), images (Cheddad et al., 2010; Chan and Cheng, 2004; Luo et al., 2011; Mohammad et al., 2011; Zhao and Luo, 2012), audio (Zhu et al., 2011), video (Al-Frajat et al., 2010).
The digital Steganography involved a carrier medium Cover such as a document, audio (Zhu et al., 2011) or an image which supported fractionation. The data to be embedded was the secret message and the medium after the embedment the stego image (Amirtharajan and Rayappan, 2012a-d; Amirtharajan et al., 2012). The choice of the algorithm is driven by parameters such as Integrity, robustness, capacity and availability (Hmood et al., 2010a, b). The other factor that drives the choice of algorithm is the domain in which the data is encoded i.e. spatial domain (Amirtharajan and Rayappan, 2012a, c; Thanikaiselvan et al., 2011) and frequency domain (Amirtharajan and Rayappan, 2012d).
In this day and age Steganography finds its applications in diverse fields (Janakiraman et al., 2012a, b; Thenmozhi et al., 2012). To quote few, in photography, aperture size, shuttle speed and other settings may be embedded in the picture itself for future references without degrading the fidelity of the image (Cheddad et al., 2010). Another scenario is the case in which a person would want to keep a file containing private information unknown to anyone (Stefan and Fabin, 2000). This technique can also be used to embed patient information within the medical imagery. Despite these many friendly applications, steganography may be outrageously used in spying and evil plots by terrorists. Consequently, it has gained a great deal of attention from political and academic institutes (Amirtharajan and Rayappan, 2012a, d; Amirtharajan et al., 2012).
Steganography owns a number of benefits for instance; only experts can study and analyze the digital files, abundance of images and patterns for use etc. One of the main boons is it stands all sorts of digital files which are very common in commercial and non-commercial ventures. Thus researches are rapidly increasing in this enchanting domain making it so vast to unearth new concepts and methodologies of diverse origin and its counter attack called steganalysis (Qin et al., 2010).
This study is a valuable means of image steganography wherein both cryptographic and steganographic security is guaranteed. This plot takes image compression and encryption as backbone and the result (preprocessed image) submits itself to steganography all the way through K-bit embedding. Thus, this combo offers additional security to images-with-secret being transferred.
Information hiding techniques are classified as irreversible (Amirtharajan and Rayappan, 2012a, d; Amirtharajan et al., 2012) and reversible methods (Zhao and Luo, 2012). In irreversible data hiding receiver can get only the surreptitious message from its stego output (Zanganeh and Ibrahim, 2011). But in the second method receiver can revive both the cover and secret information without any distortion. Irreversible data hiding method offers remarkable hiding competence and visual quality but recovery of cover image is not possible. Reversible methodologies find application in communicating sore information for instance of medicinal and military origin. The execution of two-sided entrenching algorithm is appraised via the extent of payload capability, visioning quality on the stego image, complexity of the algorithm (Padmaa et al., 2011). The different types of reversible steganography may be mentioned as pure, public and secret key (Stefan and Fabin, 2000).
Pure steganography: Pure steganographic routine embeds the data in to the cover image without using private keys. This type of steganography doesnt provide the better security because it is easy for extracting the message if the unauthorized `person becomes aware of the rooting procedure.
Secret key steganography: It is another process of steganography is similar to symmetric key algorithm. It uses the same key for embedding the data into cover in addition to extract data from it.
Public key steganography: This type of steganography uses two unlike keys one to encrypt and another key to decrypt. The key used for encryption is a private key and public key be in support of decryption.
For both encrypting and decrypting text messages using the secret keys, steganographic system uses algorithms known as steganographic algorithms. The mostly used algorithms for embedding data into images are:
|•||LSB (Least Significant Bit)|
LSB algorithm: LSB substitution aligns the cover pixels least significant bits (Chan and Cheng, 2004). This is one simpleton practice for infixing message into the image. Within images, modification of bits in the last four LSBs wont cause any change for humans eye perceptibility. The four LSB inclusions change as per the bits contained in the image. For 8 bit images, the 8th bit in every byte is altered to that of the secret. For 24 bit images, the colors in all components like RGB are changed. LSB sounds good for BMP image formats as they endure lossless compression. However, one should use an outsized image as carrier.
JSteg algorithm: This steganographic technique is used for embedding data into JPEG images. The hiding process will be done by replacing Least Significant Bits (LSB). Jsteg modus operandi supersedes LSBs belonging to quantized Discrete Cosine Transform (DCT). In this process the hiding means bounds off the entire coefficients having values of 0 or else 1. This algorithm is resistant to visual attacks and proffers venerable capacity. By and large, Jsteg means buries the covert message within images of lossy compression. This work delivers high capacity and compression ratio of 12%. JSteg algorithm is restricted for visual attacks and it is less immune for statistical attacks. Normally, JSteg embeds only in JPEG images (Zhang et al., 2009).
F5 algorithm: Westfeld (2001) introduced F5 run with the intention of avoiding the security problem when embedding the data into the JPEG images. It engrafts the secret information in stochastically selected coefficients of Discrete Cosine Transform. It utilizes matrix to implant which reduces the alterations to be made to the length of certain message. The F5 Algorithm provides high steganographic capacity and can prevent visual attacks. F5 algorithm is also resistant to statistical attacks. This algorithm uses matrix encoding such that it reduces the modification needed to root data of definite extent. It also prevents chi-square test as there is no swapping or proxy of bits. This kind of confrontation is soaring for arithmetical and visual assaults. F5 has eminent embedding capability (above 13%) supporting various image formats. Its recital diverges as per data source and cover file.
In this study, a data hiding technique had been proposed to enhance the secrecy of the data with encryption and compression. Secret data was compressed with shanon-fano encoding technique and encrypted using the rail fence cipher followed by ceaser cipher. The encrypted secret was embedded in cover image with the help of key based embedding method. The block diagram of this study is shown in Fig. 1. Observational results of images for this scheme and that of the LSB method are revealed in Fig. 2-4.
|Fig. 1:||Block diagram for proposed system|
Algorithm for embedding
Algorithm for rail fence cipher
Algorithm for recovery
RESULTS AND DISCUSSION
The algorithm is modeled in MATLAB 7.1 with Lena, Flower and Temple as the cover images. The observed results are tabled and compared with simple LSB method. From the table, it is noticed that Flower image has higher PSNR value of 62.34dB, which is much above 33 dB, fair value of imperceptibility.
|Fig. 2(a-c):||Flower image (a) Cover image (b) Stego image for proposed method and (c) Stego for LSB|
|Fig. 3(a-c):||Lena image (a) Cover image (b) Stego image for proposed method and (c) Stego for LSB|
|Fig. 4(a-c):||Temple image (a) Cover image (b) Stego image for proposed method and (c) Stego image for LSB|
Thus all the three images exhibit good imperceptibility. In simple LSB substitution also, Flower image has high PSNR; but the proposed method has more of its nature.
|Table 1:||MSE, PSNR values for proposed method and simple LSB method|
Image parameters are expressed as:
where, Ci, j is the original image and Oi, j is the stego image:
where, Imax is the 255 for colour image.
Analytical results of this study for the three images and its comparison with the existing LSB method is given in Table 1. As far as Temple image is concerned, the PSNR value differs by a considerable margin thus increases the importance of the suggested routine. This is, of course, likely the case for Lena image too. From planes point of view, in simple LSB Blue offers rich characteristics while Red plane takes the credit in proposed method. Moreover, steganalysis is an incubus task since unless and until one knows about the maneuver of compression and encryption. But which is in this case is a baffling one. Needless to mention here is the difficulty and refuge the paper offers thus making it skillful in all bounds of steganography.
With the fruition in technology in various bailiwicks people are heading towards up-to-the-minute platform in all the things which indeed has come up with out of the question security issues. Since all sorts of image processing are now being practiced widely, plentiful offenses have also been witnessed. This is where cryptography and steganography come into play. Both being antediluvian, their electronic versions are now being employed extensively in communicating cloistered information. This study paints one more picture in image steganography by meshing two broad knowledge bases namely compression and encryption. Both cryptographic and steganographic security is guaranteed and is justified by the tentative results. Moreover, stego images also leave no trace to hunch. Thus, this study is determined to be good when compared with simple LSB substitution and brags about its commercial effectuation.
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