Key Substitution Attacks on Provably Secure Short Signature Schemes
Recently, Boneh et al. proposed provably secure short signature schemes in the standard model and in the random oracle model respectively. In this letter, we propose strong-key substitution attacks on these signature schemes. In one of the attacks, we show that an adversary can generate a new public key satisfying all legitimate signatures created by the legitimate signer.

title: Low-power group key agreement for heterogeneous wireless networks
abstract: Heterogeneous wireless networks are gaining popularity as users can be connected to these networks without any cables and even when they are mobile. The high power nodes in heterogeneous wireless networks do not have energy constraints but the user nodes, which can be large in numbers, are usually low power energy constrained devices. Therefore, the GKA protocol used to secure group communications in these networks has to take into consideration both the low power nature of the user nodes and the network size. In this paper, we present an energy efficient and scalable GKA protocol, which uses our proposed Contributory Ring-Centralized (ContRi-Central) group model. Besides providing complexity analysis, we also show the computational and communication energy consumption costs analysis of all nodes running our proposed scheme and four other efficient GKA protocols. Both the complexity analysis and energy consumption costs analysis indicate that our proposed scheme is more efficient and suitable for heterogeneous wireless networks.

title: Energy-efficient ID-based group key agreement protocols for wireless networks
abstract: One useful application of wireless networks is for secure group communication, which can be achieved by running a group key agreement (GKA) protocol. One well-known method of providing authentication in GKA protocols is through the use of digital signatures. Traditional certificate-based signature schemes require users to receive and verify digital certificates before verifying the signatures but this process is not required in ID-based signature schemes. In this paper, we present an energy-efficient ID-based authenticated GKA protocol and four energy-efficient ID-based authenticated dynamic protocols, namely join, leave, merge and partition protocol, to handle dynamic group membership events, which are frequent in wireless networks. We provide complexity and energy cost analysis of our protocols and show that our protocols are more energy-efficient and suitable for wireless networks.

title: Analysis of improved signcryption scheme with key privacy
abstract: In this paper, we analyse the Yang-Wong-Deng signcryption scheme [G. Yang, D.S. Wong, X. Deng, Analysis and improvement of a signcryption scheme with key privacy,  Security Conference--ISC'05,  2005, ] proposed in ISC'05, which is the improvement and enhancement of the security of Libert-Quisquater signcryption scheme [B. Libert, J.J. Quisquater, Efficient signcryption with key privacy from gap Diffie-Hellman groups,   2004, pp. 187-200]. Although Yang et al. [G. Yang, D.S. Wong, X. Deng, Analysis and improvement of a signcryption scheme with key privacy,  Security Conference--ISC'05,  2005, ] proved that their scheme is secure against adaptive chosen ciphertext attacks and achieves ciphertext anonymity (which is also called key privacy) in the random oracle model; we disprove all their claims and show that their scheme is not semantically secure and does not achieve ciphertext anonymity.

title: Key Substitution Attacks on Some Provably Secure Signature Schemes

title: Authenticated Broadcast Encryption Scheme
abstract: With the advancement of wireless networks and mobile access devices such as cell phones and PDAs, multimedia services could be offered through wireless broadcast networks to these mobile devices. Therefore, there is a need to securely deliver multimedia content/data to many users over an insecure channel. Broadcast encryption scheme could provide this solution. The first formal study of broadcast encryption scheme is by Fiat and Noar in 1993. Since then, many broadcast encryption schemes have been proposed to improve the efficiency which is measured by three parameters, that is, length of transmission messages, users' storage and computational overhead at a user device. Some broadcast encryption schemes require less users storage, but the length of transmission messages or computation overhead depends on the number of users. In this paper, we proposed an authenticated broadcast encryption scheme which has an additional property than current proposed broadcast encryption schemes, that is, all users can verify who the sender is. The proposed scheme is proved to be secure against chosen ciphertext attacks based on the decision l-bilinear Diffie-Hellman exponent assumption. Furthermore, the simulation results, transmission messages nearly independent of the number of users and reasonable user storage show that the proposed authenticated broadcast encryption scheme is efficient and suitable for mobile devices.

title: Edge-preserving prefiltering for document image binarization
abstract: We propose a novel coplanar filter, which exploits the coplanarity of the gray-level distribution of neighboring pixels, to pre-filter document images. Experiments show that the proposed filter exhibits the following desired properties for document image binarization: (1) impulsive noise removal; (2) piecewise smoothing; (3) sharp edge preservation.

title: A model of stroke extraction from Chinese character images
abstract: Given the large number and complexity of Chinese characters, pattern matching based on structural decomposition and analysis is believed to be necessary and essential to off-line character recognition. The paper proposes a model of stroke extraction for Chinese characters. One problem for stroke extraction is how to extract primary strokes. Another major problem is to solve the segmentation ambiguities at intersection points. We use the degree information and the stroke continuation property to tackle these two problems. The proposed model can be used to extract strokes from both printed and handwritten character images.

title: Adaptive Region Growing Color Segmentation for Text Using Irregular Pyramid
abstract: This paper presents the result of an adaptive region growing segmentation technique for color document images using an irregular pyramid structure. The emphasis is in the segmentation of textual components for subsequence extraction in document analysis. The segmentation is done in the RGB color space. A simple color distance measurement and a category of color thresholds are derived. The proposed method utilizes a hybrid approach where color feature based clustering followed by detailed region based segmentation is performed. Clustering is done by merging image color points surrounding a color seed selected dynamically. The clustered regions are then put through a detailed segmentation process where an irregular pyramid structure is utilized. Dynamic and repeating selection of the most suitable seed region, fitting changing local condition during the segmentation, is implemented. The growing of regions is done through the use of multiple seeds growing concurrently. The algorithm is evaluated according to 2 factors and compared with an existing method. The result is encouraging and demonstrates the ability and efficiency of our algorithm in achieving the segmentation task.

title: Text/graphics separation using agent-based pyramid operations
abstract: This paper describes a document image analysis system using multiple agents working on a pyramid structure to separate text from graphics in the image. Text strings appear as different groupings of connected components at different image resolutions. As such, the pyramid structure, which is a multi-resolution image representation, provides a natural means of identifying and grouping of character strings in the document at different levels of resolution. The pyramid structure is also amenable to parallel processing, where multiple agents in the system can individually and concurrently look for groups of connected components at appropriate levels. The agent-based pyramid operations do not require expensive feature analysis among different connected components to detect text strings as found in other existing works.

title: Elliptic arc vectorization for 3D pie chart recognition
abstract: In this paper, we present a novel approach to vectorize elliptic arcs for 3D pie chart recognition and data extraction. As a preprocessing step, a set of straight line segments are obtained first. By estimating the parameters based on the line segments, we are able to generate elliptic arc candidates. Curve fitting is then performed to reject false positives and further refine the parameters of each elliptic arc. The vectorized elliptic arcs are the key components in the 3D pie charts that allow us to determine the chart type and to extract data values embedded. Experiments using a group of testing images show that the proposed method works well and is computationally efficient.