Multi-Participant Encryption-Steganography...
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Multi-Participant Encryption-Steganography Technique Hamdy M. Mousa Faculty of Computers and Information, Menoufia University, Egypt [email protected] Abstract: The security is very important when transmitting sensitive data through internet. The paper proposes multi- participant encryption-steganography technique (M-PEST) for images in order to make the technique more protection and less predictable. In this technique, sort the secret image pixels and divide the sorted image index into multi-participant with same size of secret image. Then, encrypt multi-participant and sorted image pixels, transpose and rotate them. After that, generate the keys vector that embedded into cover image using bit exchange method. Transmit the encrypted sorted image pixels and multi- participant indices in image format file. The keys vector is used to decrypt the secret image. Experimental results demonstrate that M-PEST technique has multilayer protection stages against different attacks and higher level of security based on the multi- sharing and difference between histograms of the secret image and multi-participant so, encrypted multi-images are acceptable. The reconstructed image is same as secret original. Keywords: Data sorting, multi-share, cryptography, bit exchange, hiding technique. 1. Introduction Maintaining the secrecy and confidentiality of images is very important when transmitting them over secured or unsecured channel. Cryptography is the technique of keeping private information from unauthorized access but authorized parties can decode it [1]. The oldest encrypted text or cipher text was found in ancient Egypt. The common technique that used to maintain security of image in storage and transmission over the network is encryption. But encryption is not enough for protection and steganography provides further security by hiding the secret text into a seemingly invisible image [2]. Visual cryptography is encryption technique to hide sensitive information in images. The secret sharing scheme divides the image into different shares and distributes them. The original image is revealed, when the shares are superimposed [3]. Noar and Shamir in 1994 are proposed Visual cryptography that is applied the Human visual system to decrypt the secret image without any computational and cryptographic algorithms [4]. The proposed scheme is involved breaking up the image into n shares so that only someone with all n shares could decrypt the secret image by superimposing the shares. They assume that the image is composed of black and white pixels, and each pixel is encrypted separately. In a (2, 2) Visual cryptography scheme, the original image is divided into two shares such that each pixel is replaced with a non-overlapping block of two or four sub- pixels in the original image. The original image will be decoded if there are all shares. In this scheme the black pixels can be reconstructed perfectly but the white pixels cannot [5, 6]. The Visual cryptography scheme is a secure method that provides authentication by breaking image into shares [7, 8]. A visual cryptography scheme for a set P of n participants is a method to encode a secret image into n shadow images called shares, where each participant in P receives one share. The secret image is recovered by using certain qualified subsets of participants, but other, forbidden, sets of participants have no information on secrete image [9, 10, 11]. A k-n secrete sharing visual cryptography scheme for color image where encryption of image is done using random number generator [12]. A (2, N) visual cryptography technique can be used in banking application [13]. The visual cryptography schemes were applied to only black and white images until the year 1997. Verheul and Van Tilborg [14] is the first colored visual cryptography scheme. A colored secret image uses the concept of arcs to construct a colored visual cryptography scheme. One pixel is transformed into m sub pixels, and each sub pixel is divided into c color regions in c-colorful visual cryptography scheme. But in both of the schemes, the shares generated were meaningless. Chang and Tsai [12] implemented color visual cryptography scheme for sharing a secret color image and also to generate the meaningful share to transmit secret color image. In the color visual cryptography for a secret color image there are two significant color images are selected as cover images which are the same size as the secret color image. Pixel expansion and the quality of the reconstructed secret image have been a major issue of visual secret sharing schemes that maintains the perfect security and the size of the original image. The paper introduces multi-participant Encryption- Steganography technique (M-PEST) for any images types. In this technique, the secret image pixels are sorted and the sorted image index is partitioned into participants with same size of secret image. Then, encode participants’ matrices and sorted image pixels using different keys and Int'l Conf. Information and Knowledge Engineering | IKE'15 | 175
Transcript of Multi-Participant Encryption-Steganography...
Multi-ParticipantEncryption-Steganography Technique
Hamdy M. Mousa Faculty of Computers and Information, Menoufia University, Egypt
Abstract: The security is very important when transmitting sensitive data through internet. The paper proposes multi-participant encryption-steganography technique (M-PEST) for images in order to make the technique more protection and less predictable. In this technique, sort the secret image pixels and divide the sorted image index into multi-participant with same size of secret image. Then, encrypt multi-participant and sorted image pixels, transpose and rotate them. After that, generate the keys vector that embedded into cover image using bit exchange method. Transmit the encrypted sorted image pixels and multi-participant indices in image format file. The keys vector is used to decrypt the secret image. Experimental results demonstrate that M-PEST technique has multilayer protection stages against different attacks and higher level of security based on the multi-sharing and difference between histograms of the secret image and multi-participant so, encrypted multi-images are acceptable. The reconstructed image is same as secret original.
Keywords: Data sorting, multi-share, cryptography, bit exchange, hiding technique.
1. Introduction
Maintaining the secrecy and confidentiality of images is very important when transmitting them over secured or unsecured channel. Cryptography is the technique of keeping private information from unauthorized access but authorized parties can decode it [1]. The oldest encrypted text or cipher text was found in ancient Egypt. The common technique that used to maintain security of image in storage and transmission over the network is encryption. But encryption is not enough for protection and steganography provides further security by hiding the secret text into a seemingly invisible image [2]. Visual cryptography is encryption technique to hide sensitive information in images. The secret sharing scheme divides the image into different shares and distributes them. The original image is revealed, when the shares are superimposed [3].
Noar and Shamir in 1994 are proposed Visual cryptography that is applied the Human visual system to decrypt the secret image without any computational and cryptographic algorithms [4]. The proposed scheme is involved breaking up the image into n shares so that only someone with all n shares could decrypt the secret image by superimposing the shares. They assume that the image is composed of black and white pixels, and each pixel is encrypted separately.
In a (2, 2) Visual cryptography scheme, the original image is divided into two shares such that each pixel is replaced with a non-overlapping block of two or four sub-pixels in the original image. The original image will be decoded if there are all shares. In this scheme the black pixels can be reconstructed perfectly but the white pixels cannot [5, 6]. The Visual cryptography scheme is a secure method that provides authentication by breaking image into shares [7, 8]. A visual cryptography scheme for a set P of n participants is a method to encode a secret image into n shadow images called shares, where each participant in P receives one share. The secret image is recovered by using certain qualified subsets of participants, but other, forbidden, sets of participants have no information on secrete image [9, 10, 11]. A k-n secrete sharing visual cryptography scheme for color image where encryption of image is done using random number generator [12]. A (2, N) visual cryptography technique can be used in banking application [13].
The visual cryptography schemes were applied to only black and white images until the year 1997. Verheul and Van Tilborg [14] is the first colored visual cryptography scheme. A colored secret image uses the concept of arcs to construct a colored visual cryptography scheme. One pixel is transformed into m sub pixels, and each sub pixel is divided into c color regions in c-colorful visual cryptography scheme. But in both of the schemes, the shares generated were meaningless. Chang and Tsai [12] implemented color visual cryptography scheme for sharing a secret color image and also to generate the meaningful share to transmit secret color image. In the color visual cryptography for a secret color image there are two significant color images are selected as cover images which are the same size as the secret color image. Pixel expansion and the quality of the reconstructed secret image have been a major issue of visual secret sharing schemes that maintains the perfect security and the size of the original image.
The paper introduces multi-participant Encryption-Steganography technique (M-PEST) for any images types. In this technique, the secret image pixels are sorted and the sorted image index is partitioned into participants with same size of secret image. Then, encode participants’ matrices and sorted image pixels using different keys and
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the encrypted keys vector is generated and embedded into host image. Transmit host image and the encrypted image pixels and participants’ matrices in image format file. Experimental results prove that reconstructed image is typical copy of secret image. And they also demonstrate that proposed technique maintains the perfect security and the size of the original image. The paper is structured as follows: in section 2, M-PEST is explained, and then in section 3 experimental results and discussion and we prove that it satisfies the presented security. Finally, the last section is conclusion.
2. M-PEST Technique
In many applications, the need of security increases. Encryption is a common technique that has application in various fields includes internet communication, medical imaging and military communication.
The encryption is not sufficient so steganography is the supplementary to encryption. It is not the replacement of encryption. But, steganography beside to encryption makes sensitive data more security. In this paper, M-PEST is proposed to protect any type of gray and RGB images. The main steps of M-PEST are explained as the following.
At the beginning, read secret Image (I1) and separate it to three components if it is RGB image. Then, convert each component to vector. For every component vector, sort its pixels and the resulted index are partitioned to three vectors using two keys or three keys according to the algorithm for
making the resultant an 8 bit image in range 0 to 255. Then, encrypt four vectors (three index partitions and image pixels’ component) using only one key or more. Reshape four vectors to original image size. After that, divide these 4/12 images into blocks and transposition some blocks of images and/or rotate left/right. At this moment, construct keys vector that contains the algorithm number, images arrangement, keys values, rotation and transposition. Embed the keys vector into cover image (I2). In the embedded stage, the threshold value can be used that achieved this condition; the pixel value is greater than even threshold value dependent on the algorithm number that used. The algorithm number is embedded in predefined bits in cover image and defines the arrangement of keys vectors and the length of each key, rotation and its direction; transposition blocks number, block size and the threshold use or not and its value. The generated keys vector may be:
AlgNo, Key1, Key2, Key3, ……. , ImagesArrangement, Rot, Dir, blockSize, BlockTrans, …… , .....
In general all ranges doesn’t defined or limited in M-PEST, but in our implementation, the range of AlgNo is from 1 to 10, the block size varies from 8 pixels to 50% of image size range, there are no more 5 block transposition and one time left/right shift with shifting value from 0 to 20% of Image Size range. There is an example of Keys vectors that is shown in Figure 1.
Fig. 1: keys vectors example
In the Embedded keys vector stage, read and prepare cover file and the starting pixel to embed the vector is previously defined, the encrypted keys vector is embedded into the cover file by changing the least significant bit.
The Pseudocode of Encoding and Decoding secure multi-participant Encryption-Steganography are shown in Fig. 2 and Fig. 3.
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Fig. 2: Pseudocode of proposed encoding-encryption
Fig. 3: Pseudocode of proposed decoding - encryption
3. Implementation and Evaluation Results
The M-PEST technique is implemented using MATLAB 2009 on Windows 7 platform and run the program with different size and type secret images and different cover images types.
In this section, some experiments are carried out to prove the efficiency of the proposed M-PEST technique. The original image, reconstructed-image and cover image are shown in Figure 4. The peak signal-to-noise ratio (PSNR) represents the ratio between the maximum possible power of a signal and the power of corrupting noise that affects the fidelity of its representation. On reconstructing the secret image is obtained back without any loss. The quality of the secret image can be analyzed by using the PSNR value of original secret image and reconstructed image. The value of PSNR is infinity, meaning that the two images are identical. The PSNR value of cover image before/after embedding keys vector is greater than 50 dB. The twelve encrypted images are shown in Figure 5.
Secret Image Reconstructed Secret Image Cover Image Fig. 4: The original secret images and encrypted images
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Encrypted Image 1 Encrypted Image 2 Encrypted Image 3 Encrypted Image 4
Encrypted Image 5 Encrypted Image 6 Encrypted Image 7 Encrypted Image 8
Encrypted Image 9 Encrypted Image 10 Encrypted Image 11 Encrypted Image 12 Fig. 5: encrypted image components
4. Experimental Results Analysis
A good encryption procedure should be robust against all kinds of cryptanalytic, statistical and brute-force attacks. Thus, the histogram of the encrypted images must be different from the original one to avoid statistical attacks, and the key space must be large enough to avoid brute force attacks. The M-PEST technique achieved the previous encryption requirements. Below performance analysis of the M-PEST technique shows that it is indeed robust against possible attacks.
4.1 Histogram Analysis Visual attacks are the simplest and most important types
of steganalysis. In a visual attack, the cipher-image is examined with the naked eye to identify any obvious inconsistencies. Figure 6 shows the secret image components, their corresponding cipher images and their histograms. It is clear that the histograms of the encrypted
images are considerably different from the histogram of the original image. So the encrypted image does not provide any indication to utilize any statistical attack on the M-PEST, which makes statistical attacks difficult.
4.2 Key Space Analysis The M-PEST technique has large key space that making
brute force attack is infeasible. The M-PEST technique has different combinations of the secret keys. A cipher with such as a long key space is sufficient for practical use in secure cryptosystem and it’s also threshold value.
Thus, the M-PEST technique makes larger statistical changes in the transmitted images and more secure. Experimental results demonstrate that proposed technique can defeat many existing steganalytic attacks. It is also have higher level of security against some existing attacks based on the multi-participant image index and encrypted keys and transposition and rotation.
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Fig. 6: Secret Image components, Encrypted Images and their histograms
5. Conclusions
In this paper, multi-participant encryption-steganography technique (M-PEST) is implemented for gray and color images. The M-PEST technique that is more secured encryption-steganography technique based on multi-participant images. This technique embeds the sensitive
information into host image using bit exchange and divide index to multi-index matrices. It is also encrypting, rotating and transposing some blocks of the sorted secret image and its indices.
The results show the resistance of the M-PEST technique against different steganalytic attacks based on very large key space and different combinations. The changes of histograms of the secret image and its encrypted-images are
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significant. The mean-squared error value between the original images and reconstructed images is zero. Furthermore, they show it has multilayer protection stages and achieves confidentiality and gives more security, effectiveness and robustness to data and protects against detection. In future work, we will be extended M-PEST technique for video and audio encryption. We try to use proposed technique to reduce the transmitted images size and enhance the encrypted-images quality.
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