3D Res. 04, 01(2013)1 10.1007/3DRes.01(2013)1
3DR EXPRESS
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Pattern Based 3D Image Steganography
P. Thiyagarajan • V. Natarajan • G. Aghila • V. Prasanna Venkatesan • R. Anitha
Received: 23 February 2012 / Revised: 26 September 2012 / Accepted: 26 October 2012 © 3D Research Center, Kwangwoon University and Springer 2013
Abstract * This paper proposes a new high capacity Steganographic scheme using 3D geometric models. The novel algorithm re-triangulates a part of a triangle mesh and embeds the secret information into newly added position of triangle meshes. Up to nine bits of secret data can be embedded into vertices of a triangle without causing any changes in the visual quality and the geometric properties of the cover image. Experimental results show that the proposed algorithm is secure, with high capacity and low distortion rate. Our algorithm also resists against uniform affine transformations such as cropping, rotation and scaling. Also, the performance of the method is compared with other existing 3D Steganography algorithms. Keywords Information hiding, 3D steganography, Triangle Mesh Formation, Cover Image, Stego Image, Spatial Domain.
1. Introduction Development of digital media in internet, wide spread use of personnel computers and multimedia applications permit users to hide the information in digital medium (such as image, audio, video and electronic documents) and distribute it through unsecure channels. On the other hand, it also implies the danger that valuable contents may easily be detected, duplicated, modified by an unauthorized user. As a technique to protect the secret information hidden in P. Thiyagarajan1 ( ) • V. Natarajan2 ( ) • G. Aghila1 ( )• ) • R. Anitha2 ( ) V. Prasanna Venkatesan1 ( 1 CDBR-SSE Lab, Department of Computer Science, School of Engineering and Technology, Pondicherry University, Puducherry -14. 2 CDBR-SSE Lab, Department of Mathematics and Computer Applications, PSG College of Technology, Coimbatore - 04. E-mail:
[email protected],
[email protected],
[email protected],
[email protected], and
[email protected]
the digital media and to detect the unauthorized tampering of it, information hiding is now attracting large attentions in the field of information security. Steganography is the science which deals with the information hiding into digital medium1. In Steganography, the secret data is embedded into the Cover digital medium by an embedding algorithm that produces the Stego digital medium. Once the Stego digital medium reaches the destination, extracting algorithm is used to extract the secret message embedded in it. Nowadays three-dimensional (3D) geometric models are becoming an important part of the multimedia content. There are valuable products of intellectual activities in the computer graphics field. The advance of distributed engineering environment and virtual space construction technology open the opportunities to globally distribute and exchange the geometrical models through computer networks. Such background has prompted researchers to extend the realm of steganography from the traditional media such as images, sounds and videos to 3D geometric models. In this paper, we propose a new technique for embedding information into 3D geometric models by constructing triangle meshes. The proposed algorithm re-triangulates a part of a triangle mesh and embeds the secret information into the positions of the newly added vertices. Up to 9 bits data can be invisibly embedded into a vertex of the triangle without causing any changes to the geometrical structure and visibility of the original 3D image model. The embedded secret information resists many of the geometrical attacks. The next section briefs the requirement of steganography and detailed survey of the existing Steganographic techniques for 3D image models. Section 3 describes the basic idea and details of proposed embedding and extraction algorithm. Section 4 discusses the performance evaluation and section 5 gives the conclusion.
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3D Res. 04, 01(2013)1
2. Survey of State of the Art – 3D Steganography Algorithms The existing Steganographic techniques can be classified either as spatial domain techniques or frequency domain techniques based on their approaches. The spatial domain methods embed the information by modifying the original image data directly, whereas the frequency domain approaches transform the original data into frequency domain first and then embed the secret information there. Recent researches on 3D image model steganography are mainly focusing on the spatial domain methods. In spatial domain, the patterns of 3D models in geometry are usually classified into mesh model or point cloud model. 3D mesh model normally consist of vertices, edges and polygonal surfaces while point sample model consists of 3D geometry. However, 3D point cloud model consists of point information only which is a basic element of information hiding. Finding a way to fully exploit the features of 3D point cloud models is a challenging research problem. Ohbuchi et.al.2-5 presented a sequence of watermarking algorithms for polygonal meshes. However, their approaches are not robust enough to be used for copyright protection. Cotting et al.6 proposed a watermarking algorithm of point sampled geometry based on pseudo spectral analysis. This algorithm partitioned the model into a set of patches by applying a fast hierarchical clustering scheme. Wang and Wang7 presented a data hiding scheme for point models. The scheme used Principal Component Analysis (PCA) and symmetrical swap procedure to embed messages. This algorithm suffers from capacity drawback that the data capacity in bits generally achieved is only about half of the number of points in the model. Cheng et al.8-10 described a data hiding scheme for point models based on a substitute procedure. The virtual multilevel embedding procedure is used to embed three bits per point based on shifting the message point by its virtual
sliding, extending and arching geometrical properties. Luo et al.11 presented a reversible data hiding for 3D point cloud model. It started with creating a set of eight neighbor vertices clustered set with randomly selected seed vertices. Next, an eight neighbor integer DCT was performed to obtain coefficient. Finally, the highest frequency coefficient modification technique was employed to embed messages. The scheme has the characteristic of reversibility but of very low capacity. Ke Qi et al.12 proposed a new high-capacity spatial steganography scheme for 3D point cloud models using a Self – Similarity position matching procedure. This scheme partitions the 3D point cloud model into patches. These patches are grouped by using self similarity measures which generates the codebook. The technique can be considered as a side-match steganography and has proven to be a feasible alternative to other steganography schemes for 3D point cloud model. In the transform domain methods, Cotting et al.,6 and Wang et al.,7 techniques have high robustness but low capacity whereas spatial domain method reported by Cheng et al.,8 and Luo et al.,11 have high capacity but low robustness. Both Spatial and Frequency domain fails to address the important parameter which is the security. Since, steganography requires security, high capacity and high robustness, in this paper we propose to develop a secure high capacity, blind scheme in spatial domain. This study presents a new blind high capacity steganography for 3D images, based on pattern identification. The key idea is to construct triangle meshes for given cover 3D image model through the triangle subdivision process. This procedure efficiently achieves embedding capacity of around three bits per vertex of the triangle mesh. In this proposed Steganographic algorithm, unlike the conventional schemes stego key is used for both dynamic embedding and also triangle subdivision. Thus security is ensured by stego key.
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(b) Figure 1 (a) Embedding Process (b) Extracting Process.
3D Res. 04, 01(2013)1
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3. The Proposed method The novelty of the proposed steganography algorithm is that stegokey is generated from the message to be embedded. This Stegokey is used to form the triangle mesh and it is also used for embedding. Figure 1 illustrates the overview of embedding and extracting process of pattern based 3D Steganography method. The proposed algorithm is a spatial domain scheme with the following four modules: a) Stego Key Generation b) Triangle mesh formation c) Embedding d) Extraction
3.1 Stego-Key generation The generation of stego-key is based on the secret message to be embedded. Since the key generation process is dependent on the message to be embedded, for the same cover image, different keys will be generated for different secret messages which doubly ensure security. The following steps explain the steps involved in Stegokey generation: Step 1: Convert each and every character of the secret
message to be embedded into its corresponding ASCII value and then convert it in its binary form M Step 2: Divide the binary message M into 3 bits blocks M1, M2, … Mk by padding with zeros if necessary Step 3: Convert M1, M2… Mk into the corresponding decimal values d1, d2,…dk Step 4: Find the minimum (min) and maximum (max) of each di, 1
