lin Qi

An efficient water-filling algorithm for power allocation in OFDM-based cognitive radio systems

In this paper, we present a new water-filling algorithm for power allocation in Orthogonal Frequency Division Multiplexing (OFDM) - based cognitive radio systems. The conventional water-filling algorithm cannot be directly employed for power allocation in a cognitive radio system, because there are more power constraints in the cognitive radio power allocation problem than in the classic OFDM system. In this paper, a novel algorithm based on iterative water-filling is presented to overcome such limitations. However, the computational complexity in iterative water-filling is very high. Thus, we explore features of the water-filling algorithm and propose a low-complexity algorithm using power-increment or power-decrement water-filling processes. Simulation results show that our proposed algorithms can achieve the optimal power allocation performance in less time than the iterative water-filling algorithms.

A novel active warden steganographic attack for next-generation steganography

Digital steganography is often divided into two categories of research: steganographer and attacker, where a steganographer attempts to successfully hide the existence of hidden data and an attacker attempts to uncover and destroy said data. Often steganographic attacks utilize passive techniques, where the attacker monitors messages and alters or destroys the cover media only if the media is suspected to contain a message. Passive attacks are much more prevalent than active attacks for a variety of reasons. Generally passive attacks are more efficient and effective in determining the existence of hidden data in a given cover media, however, most passive attacks are not generic enough to detect the presence of a hidden message outside of a very small subset of steganographic algorithms. Conversely, current active attacks are very cost effective and often severely degrade or destroy the quality of the cover media. In this paper, we propose a novel active steganographic attack called the Discrete Spring Transform (DST). The concept of the DST attack is that of likening the cover media to a spring, in that it can be physically altered or manipulated in a manner of ways, while the basic structure and integrity of the spring is preserved despite these alterations. Since many steganographic schemes rely on the fact that the cover media remains somewhat stable the DST is effective in destroying the stego media for such types of steganographic algorithms. It follows that the DST is an effective and highly adaptable active attack that can be applied to a variety of cover media, including video. We will demonstrate that the attack is capable of defeating next-generation steganographic algorithms, including motion-vector steganography and RST-resilient algorithms by increasing the Bit Error Rate (BER) of the steganographic algorithm to approximately 0.5 while maintaining the quality of the cover media, where the Peak Signal-to-Noise Ratio (PSNR) of the image-derived media always remains above 30db.

A video steganography attack using multi-dimensional Discrete Spring Transform

Video steganography is fast emerging as a next-generation steganographic medium that offers many advantages over traditional steganographic cover media such as audio and images. Various schemes have recently emerged which take advantage of video specific properties for information hiding, most notably through the use of motion vectors. Although many steganographic schemes have been proposed which exploit several possible steganographic domains within video sequences, few attacks have been proposed to combat such schemes, and no current attacks have been shown to be capable of defeating multiple schemes at once. In this paper, we will further expand upon our proposed Discrete Spring Transform (DST) steganographic attack. We will explore further applications of the transform and how it may be used to defeat multiple steganographic schemes, specifically current video steganography schemes. The effectiveness of the proposed algorithm will be shown by attacking a multi-dimensional steganographic algorithm embedded in video sequences, where the scheme operates in two different dimensions of the video. The attack is successful in defeating multiple steganographic schemes verified by determining the BER after DST attack which always remains approximately 0.5. Furthermore, the attack preserves the integrity of the video sequence which is verified by determining the PSNR which always remains approximately above 30dB.

Steganography attack based on Discrete Spring Transform and image geometrization

In order to prevent harmful secret information sharing by steganography, a new active-warden countermeasure approach against steganography is proposed in this paper. Differently from the other countermeasure approaches presented in current literature which need to have some knowledge of the steganographic algorithms to be attacked, our proposed method is a generic method which is independent of any particular steganography methods being utilized. In other words, our approach blindly attacks the steganography without any prior knowledge of the used algorithms or their existence. In general, the hidden information is embedded in a carrier by adjusting the coefficients of the audio or image. In our method, by exploiting the large margin between the numerical value and visual perception of the images, large amounts of visually non-detectable distortions are incurred in the image. As a result, the hidden message is destroyed by this method while the perceptual quality of the image is maintained. Inspired by the print-scan process in which most of the steganographic methods cannot survive, a transform called Discrete Spring Transform (DST) is proposed in this paper as the foundation of our attack algorithm. An image geometrization method is also developed to reconstruct the image in this paper. The simulation results have demonstrated that the PSNR of the attacked image is above 30dB with a high perceptive quality while the BER of the hidden steganographic message in the attacked image is above 0.5.

An active audio steganography attacking method using discrete spring transform

The significant development of cell phone and mobile network in recent years leads to some security concerns caused by increasing capacity of the networks and the large margin of the multimedia data. Audio steganography is a proven way to hide information in digital audio signals, where many schemes have been effective at hiding large amounts of data. In order to prevent the malicious threat of the audio steganog-raphy, the countermeasure of audio steganography is also an important topic. In this paper, we propose a novel steganographic attack which can defeat audio steganography algorithms while maintaining an acceptable audio distortion level. The attacking method is based on a proposed transform called discrete spring transform. Similar to the time scale modification, the spring transform disables the synchronization of the hidden information. Furthermore, the proposed method has some advantages over the traditional time scale modification, therefore the steganography method which can resist to the time scale modification still can be defeated by the proposed method. The simulation results show that the proposed method successfully defeat some audio steganography methods which are resistant to the time scale modification with subjective auditory quality score no worse than -0.1.

Frequency domain discrete spring transform: A novel frequency domain steganographic attack

Digital steganography explores hiding information within a given media. It is critical to develop methods which block such secret data communication. We have proposed the Discrete Spring Transform (DST) which is a steganographic attack that has been developed to combat the latest steganographic techniques. We propose a novel attack method for the DST that can attack transform domains of a cover media. The proposed technique is a stronger way to attack those steganographic methods which utilize transform domains than spatially-oriented DST. Our results indicate that the steganographic data is destroyed while the quality of the cover media is preserved.

An adaptive algorithm for corrupted images

Noise is ever-present in communication channels and can produce devastating degradation to the images at the receiver end. In this paper, a novel approach to detecting different types of noise models in corrupted images is presented. Basically, it is a two-step process that has the ability to handle real-time applications due to its computational simplicity. The proposed algorithm handles error correction more efficiently in the second stage of processing, given a means to detect the type of noise present in the first stage. This algorithm will be verified and tested against existing methods on different noise models. Preliminary results show that this methodology can accurately detect and compensate for various noise sources common in multimedia applications, such as impulse, Gaussian, and uniform noise, with minimal loss to the integrity of the original digital image.

Real-time audio steganography attack based on automatic objective quality feedback

Digital audio signal provides a large capacity for embedding hidden messages using digital steganography techniques. How to prevent hazardous steganography embedding on the Internet becomes an important task in the field of network security. For the Internet environment, the steganography attack method is required to be generic and real time. An active warden-based attack method is potential to be a generic method for the steganography attack. A discrete spring transform (DST)-based generic active warden steganography attack framework has been proposed by us. In this paper, based on the DST, a real-time steganography attack method is proposed. The potential unauthorized hidden message is removed in a real-time manner when uploading or downloading the audio signal. The real-time signal perceptual quality control is achieved by the automatic feedback from the objective audio quality evaluation model. The attack parameters are adaptively changed to reach a balance between the attack performance and the audio signal quality. The simulation results validate the proposed method in terms of the steganography attack performance and the audio signal quality after the attack. Copyright

Generic attack against robust steganography based on spring transform and geometrization

There have been many robust image steganography methods that are invented in recent decades. However, this technique also may be used by malicious users to transmit dangerous information through the Internet beyond the control of the security agencies. How to detect and/or block potentially dangerous information transmission on the Internet through billions of images while not affecting the normal digital images becomes a challenging problem. Existing steganalysis methods or steganography attacking methods cannot be used for analyzing a large volume of digital images in a short time. In this paper, we propose an effective steganography attacking method that is not limited by the types of the steganography method. The proposed method can process the digital images to remove the potentially dangerous hidden information while keeping the digital image in a high visual quality. Inspired by the way in which printers and scanners work, our method decouples the human visual perception and the digital images numerical values. It causes the numerical values of the image to change dramatically, and then the hidden information are largely damaged, while at the same time, the visual image quality can be maintained. Our experimental results have demonstrated that the peak signal-to-noise ratio of images can be above 32dB while the stego data are destroyed. Copyright