01-10-2016, 12:35 PM
1457256089-Introduction.docx (Size: 1.34 MB / Downloads: 7)
Abstract:
Text and images can be provided security by the process of steganography, an art of hidden writing. Many algorithms are implemented to hide the text and images. The proposed work is based on hiding the image inside two images as a two-step process. The two steganography algorithms, namely jsteg algorithm and RSA algorithm, are combined to enhance the level of protection for secret image. With the input image and secret image is used for concealing. Jsteg algorithm is used to connect the input image and the secret image is encrypted using RSA algorithm. The output image of jsteg algorithm is concealed in the RSA encrypted image. Thus this method enhances the protection level in such a way that the image is concealed and it makes the communication to hide the existence of image from a third party. Thus more security, confidentiality and lesser detectability is obtained and limits the unauthorized access during image transmission.
Introduction:
Steganography is a science of hiding important information by embedding messages within other, seemingly harmless messages. Steganography is different and distinct from cryptography, there are many analogies between the two, and some authors classify steganography as a form of cryptography since hidden communication is a form of secret writing. Different message hiding techniques have been developed and implemented in the past using audio/video files, digital images, and other medias[1] the proposed work makes use of two algorithms to hide an image namely jsteg and RSA images.one is such technique is digital media where digital images are used as a medium for hiding information’s in the form:text,didital image, video or audio file as secret message[2].The word steganography derived from two Greek words: stains means covered and graphs means writing and often refers to secret writing or data hiding[3].The major goal of steganography is to increase communication security by inserting secret message into the digital image, modifying the redundancy or nonessential pixels of the image[4],and is recently become important in a number of application areas especially military and intelligence agencies which require unobtrusive communications. If the presence of hidden information is suspected or even revealed, the purpose of steganography is partly defeated [5]. Data security or data privacy has become increasingly important as more and more systems are connected to the Internet. There are information privacy laws that cover the protection of data or information on private individuals from intentional or unintentional disclosure or misuse. Thus, hiding the data in a kind of form such as within an image is vital in order to make sure that security or privacy of the important data is protected[6].
Thus, A number of algorithms are used for steganography to hide the information in images. The proposed work is based on two algorithm namely jsteg and RSA to enhance the security of image transmission. These algorithms is an enhanced version of LSB technique that is not very muchrobust. Also a compression technique is used to increase the hiding capacity. Thus demonstrated using an application is built in matlab.
The rest of the paper is organized as follows: Section 2 would be presenting the use of proposed algorithms. The implementation of the system is discussed in section 3. Discussion of various results obtained from testing the system based on the proposed algorithm, with various sizes of images is explained and finally the paper is concluded along with future scope.
2:jsteg and RSA algorithms:
The first recorded uses of steganography is traced back to 440 BC when Herodotus mentions an example of steganography in the history of Herodotus.
Ancient example is that history of Herodotus who shaved his head of his most trusted slave and tattooed a message on it.After his hair had grown the message was hidden. The purpose was to instigate a revolt against the Persians.
During the “cold war “period ,US and USSR wanted to hide their sensors in the enemy facilities. These device has to send data to their nation, without being spotted.
IN the October 2001,new York times published an article claiming that qaeda had used steganography to encode message into images, and the transported these via e-mail and possibly via USENET to prepare and execute the September 11,2001 terrorist attack[12]
2.1:JPEG (joint picture expert group):
Discrete cosine transformation is very famous steganography techniques which is best suited for JPEG images. JPEG images are widely used over the internet and have lossy nature of compression. DCT is extensively used for image and video compression. Every block of DCT is quantized with the help of quantization table of JPEG. Quantized coefficients are used to embed the secret message. Afterward coding methods are applied such as Huffman coding. In this technique high frequency regions are better for information hiding as they often become zero after the process of quantization. Hence it is not necessary to modify the coefficient value if the embedded data is zero. JSteg/ JPHide, F5, YASS (Yet another stenographic scheme) and Outguess are some of the DCT steganography tools [7].For the execution of image compression in the coordination of JPEG, initial step is to convert the RGB color coordination into the coordination of YUV. In this coordination the Y component refers to matching the brightness of a pixel and the U and V components refer to the color of a pixel [8]. Currie, D.L. & Irvine, C.E. Illustrate that the human eye is very sensitive to changes in brightness of pixels more than the changes in color of pixels [9].Some samples are taken from the bottom of color data to reduce the file size when applying JPEG compression. The use of a factor 2 will reduce the size of the file, where the color components (U and V) are reduce by half in the horizontal and vertical directions [8].
Next step is to Discrete Cosine Transform (DCT) is used for the transformation of the image into JPEG, The DCT is a mathematical transform that converts a signal from coordination into frequency coordination, Through grouping the pixels into 8 × 8 pixel blocks and converting the pixel blocks into 64 DCT coefficients each. That's where all 64 pixel images in that block will be affected when any DCT coefficient is modified.
Final stage is the quantization of the compression. One form biological characteristics of the human eye can be exploited: that the human eye is rather good to distinguish between differences in brightness or (luminance) in low frequencies, but they are not good at distinguishing between differences in lighting or brightness in the high frequencies. This identify that the strength of high frequency shrunk, without any effect on the appearance of the image. To further reduce the file size, the result is rounded to the integer values and the coefficients are encoded by using Huffman coding [8].
2.2:JSteg
There are different variety of features using images in JPEG format, an image used in Steganographic applications. Initial step is the JPEG image file format has a large scale patronage and has become standard for storing and transmitting images on the network. When using this types of JPEG images in the process of concealing data, the attention of the attacker or anyone else on the resulting image is less than that with most other formats.
Second, some considerable controls are available on the quantized image. Finally, JPEG file provides the ability to hide a large amount of stenographicdata messages. [10]. Derek Upham’s JSteg was the first publicly available stenographic system for JPEG images [11].
JSteg algorithm replaces LSBs of quantized Discrete Courier Transform (DCT) coefficients. In this process the hiding mechanism skips all coefficients withthe values of 0 or 1. This algorithm is resistant to visual attacks and offers an admirable capacity for steganographic messages.[13] Generally, JSteg steganographic algorithm embedded the messages in lossy compressed JPEG images. It has highcapacity and had a compression ratio of 12%. JSteg algorithm is restricted for visualattacks and it is less immune for statistical attacks. Normally, JSteg embeds only inJPEG images. In these JPEG images, the content of the image is transformed into “frequency coefficients‟ so as to achieve storage ina very compressed format. Thereis no visual attack in the sense presented here, due to the influence of one steganographic bit up to 256 pixels.[13].
2.3:RSA
RSA was invented byfor Ron Rives, Adi Shamir and Leonard Adleman. It is the algorithm used for encrypting and decrypting messages. RSA is asymmetric key algorithm, hence using two different keys. One is private key: it is kept secret and other is public key: can be shared. Using these two keys the message is encrypted and decrypted.[14].
The RSA algorithm could be used in combination with advanced LSB in a way that original text is embedded in the cover image in the form of cipher text. By using the RSA algorithm we are increasing the security to a level above. In case of steganalysis only cipher text could be extracted which is in the encrypted form and is not readable, therefore will be secure [15]. RSA algorithm procedure can be illustrated in brief as follows:
1. Choose two large prime no. p & q.
2. Calculate N=p*q
3. Calculate f(z)=(p-1)*(q-1)Find a random number e satisfying 1 < e < f (n) and relatively prime to f (n) i.e., gcd (e, f (z)) = 1.
4. Calculate a number d such that d = e-1 mod f (n).
5. Encryption: Enter message to get cipher text. Ciphertext c= mod ((message. ^e), N).
6. Decryption: The cipher text is decrypted by : Message=mod ((c. ^d), N) [15]
3roposed method:
In this work, two algorithms are combined, namely JSteg algorithm and RSA algorithm, toenhance the level of protection for the hidden images. Once the input image is choosen,the secret image is selected and encrypted using RSA algorithm. The input image is converted intoa Jsteg converted image. This jsteg image is hided in the encrypted image. The tricky nature of hiding an already hidden image using two different algorithms introduces some complexity and makes it more deceptive to a third party, hence reducing the suspension of in the existence of a secret image and significantly enhancing the protection level.
4:Modules Design:
The proposed work is divided into the following steps:
• Image enhancement and Intensity calculation.
• Watermarking by J-steg.
• Embedding with RSA.
• Secret image and encryption.
CONCLUSIONS
This paper presented a steganographic approach that combined jsteg and RSA algorithms. The approach allowed us to benefit from the potential features and strengths of both algorithms and this added a significant level of protection to hidden images. In principle what happened in our proposed approach is that an input image and secret image is used for concealing. Jsteg algorithm is used to connect the input image and the secret image is encrypted using RSA algorithm. The output image of jsteg algorithm is concealed in te RSA encrypted image. The act of hiding an already hidden image (stego image) in another image alone is tricky and deceptive for a third party. Besides that, the idea of combining two steganographic algorithm makes the approach more complex for a third party and this increases the chances that the intended secret massage (secret image) could go unnoticed.
Furthermore, the priority given to selecting a good image sizes and type further disguises the secret image and makes it more difficult for a third party to suspect the existence of a secret image. The experimental results indicated an average PSNR value of more than 50 dB for more than100 images and that is a good and acceptable steganography scheme. As future work, we could try the combination of other steganography techniques and compare the efficiency levels, as well as adding image encryption.