A robust image watermarking scheme in curvelet domain is proposed. The curvelet transform directly takes edges as the
basic representation element; it provides optimally sparse representations of objects along edges. The image is
partitioned into blocks and curvelet transform is applied to those blocks with strong edges. The watermark consists of a
pseudorandom sequence is added to the significant curvelet coefficients. The embedding strength of watermark is constrained by a Just Noticeable Distortion model based on Barten's contrast sensitivity function. The developed JND model enables highest possible amount of information hiding without compromising the quality of the data to be protected. The watermarks are blindly detected using correlation detector. A scheme for detection and recovering geometric attacks is applied before watermark detection. The proposed scheme provides an accurate estimation of single and/or combined geometrical distortions and is relied on edge detection and radon transform. The selected threshold for watermark detection is determined on the statistical analysis over the host signals and embedding schemes. Experiments show the fidelity of the protected image is well maintained. The watermark embedded into curvelet coefficients provides high tolerance to severe image quality degradation and robustness against geometric distortions as well.
Although semi-blind and blind watermarking schemes based on Discrete Cosine Transform (DCT) or Discrete Wavelet Transform (DWT) are robust to a number of attacks, they fail in the presence of geometric attacks such as rotation, scaling, and translation. The Discrete Fourier Transform (DFT) of a real image is conjugate symmetric, resulting in a symmetric DFT spectrum. Because of this property, the popularity of DFT-based watermarking has increased in the last few years. In a recent paper, we generalized a circular watermarking idea to embed multiple watermarks in lower and higher frequencies. Nevertheless, a circular watermark is visible in the DFT domain, providing a potential hacker with valuable information about the location of the watermark. In this paper, our focus is on embedding multiple watermarks that are not visible in the DFT domain. Using several frequency bands increases the overall robustness of the proposed watermarking scheme. Specifically, our experiments show that the watermark embedded in lower frequencies is robust to one set of attacks, and the watermark embedded in higher frequencies is robust to a different set of attacks.
The problem of distributing multimedia securely over the Internet is often viewed as an instance of secure multicast communication, in which multicast messages are protected by a group key shared among the group of clients. One important class of key management schemes makes use of a hierarchical key distribution tree. Constructing a hierarchical tree based on secret shares rather than keys yields a scheme that is both more flexible and provably secure. Both the key-based and share-based hierarchical key distribution tree techniques are designed for managing keys for a single data stream. Recent work shows how redundancies that arise when this scheme is extended to multi-stream (e.g. scalable video) applications may be exploited in the key-based system by viewing the set of clients as a “multi-group”.
In this paper, we present results from an adaptation of a multi-group key management scheme using threshold cryptography. We describe how the multi-group scheme is adapted to work with secret shares, and compare this scheme with a naïve multi-stream key-management solution by measuring performance across several critical parameters, including tree degree, multi-group size, and number of shares stored at each node.
Encryption and watermarking are complementary lines of defense in protecting multimedia content. Recent watermarking techniques have therefore been developed independent from encryption techniques. In this paper, we present a hybrid image protection scheme to establish a relation between the data encryption key and the watermark. Prepositioned secret sharing allows the reconstruction of different encryption keys by communicating different activating shares for the same prepositioned information. Each activating share is used by the receivers to generate a fresh content decryption key. In the proposed scheme, the activating share is used to carry copyright or usage rights data. The bit stream that represents this data is also embedded in the content as a visual watermark. When the encryption key needs to change, the data source generates a new activating share, and embeds the corresponding watermark into the multimedia stream. Before transmission, the composite stream is encrypted with the key constructed from the new activating share. Each receiver can decrypt the stream after reconstructing the same key, and extract the watermark from the image. Our presentation will include the application of the scheme to a test image, and a discussion on the data hiding capacity, watermark transparency, and robustness to common attacks.
Security is an increasingly important attribute for multimedia applications that require prevention of unauthorized access to copyrighted data. Two approaches have been used to protect scalable video content in distribution: Partial encryption and progressive encryption. Partial encryption provides protection for only selected portions of the video. Progressive encryption allows transcoding with simple packet truncation, and eliminates the need to decrypt the video packets at intermediate network nodes with low complexity. Centralized Key Management with Secret Sharing (CKMSS) is a recent approach in which the group manager assigns unique secret shares to the nodes in the hierarchical key distribution tree. It allows the reconstruction of different keys by communicating different activating shares for the same prepositioned information. Once the group key is established, it is used until a member joins/leaves the multicast group or periodic rekeying occurs. In this paper, we will present simulation results regarding the communication and processing requirements of the CKMSS scheme applied to scalable video. In particular, we have measured the rekey message size and the processing time needed by the server for each join/leave request and periodic rekey event.