Shiuan-Tung Chen

A Shoulder Surfing Resistant Graphical Authentication System

Authentication based on passwords is used largely in applications for computer security and privacy. However, human actions such as choosing bad passwords and inputting passwords in an insecure way are regarded as “the weakest link” in the authentication chain. Rather than arbitrary alphanumeric strings, users tend to choose passwords either short or meaningful for easy memorization. With web applications and mobile apps piling up, people can access these applications anytime and anywhere with various devices. This evolution brings great convenience but also increases the probability of exposing passwords to shoulder surfing attacks. Attackers can observe directly or use external recording devices to collect users’ credentials. To overcome this problem, we proposed a novel authentication system PassMatrix, based on graphical passwords to resist shoulder surfing attacks. With a one-time valid login indicator and circulative horizontal and vertical bars covering the entire scope of pass-images, PassMatrix offers no hint for attackers to figure out or narrow down the password even they conduct multiple camera-based attacks. We also implemented a PassMatrix prototype on Android and carried out real user experiments to evaluate its memorability and usability. From the experimental result, the proposed system achieves better resistance to shoulder surfing attacks while maintaining usability.

Efficient encoding of systematic Raptor codes based on operation lists for known block lengths

Raptor codes can provide good error correction capability and efficient encoding and decoding rates. Its fountain code property is effective in avoiding packet retransmission for both unicast and multicast service delivery. Hence, there are many wireless and broadband applications adopting it such as mobile multimedia broadcasting and broadband IPTV systems. In this paper, we present an efficient systematic Raptor codes encoder based on operation lists for known block lengths. For a Raptor codes application that can frequently use one or several fixed block lengths (i.e., the number of source symbols in a source block), we could produce the corresponding operation lists in advance and use it to generate the encoding symbols more efficiently. We first introduce the basic architecture of the proposed Raptor encoder, and then describes the details about how to generate operation lists and Raptor intermediate symbols. The simulation results show that our encoder is at least two times faster than the conventional Raptor codes encoder which is adopted by 3GPP and DVB-H.

An HD streaming system for WiFi multicast channels based on application-layer FEC

This paper presents an HD (High Definition) streaming system that employs an AL-FEC (Application-Layer FEC) scheme (i.e., DVB AL-FEC) based on Raptor codes to protect the transmission of MPEG-2 TS (Transport Streaming) over RTP streaming packets over error-prone Wi-Fi multicast channels. The employed AL-FEC scheme can effectively recover the missing Wi-Fi multicast packets in a scalable way. In this paper, we describe the prototype of the proposed HD streaming system, which is implemented based on VLC server and VLC client over Linux operating systems. Finally, we show that the proposed system can significantly improve the HD video quality of a Wi-Fi multicast streaming service.

Fast and low-complexity encoding of Raptor codes based on operation lists for known source block lengths

Raptor codes can provide good error correction capability and efficient encoding and decoding rate. Its fountain code property is effective in avoiding packet retransmission for both unicast and multicast service delivery. Hence, there are many mobile, vehicular and broadband applications adopting it such as mobile multimedia broadcasting, multimedia communications for high-speed rails and broadband IPTV systems. In this paper, we present an efficient systematic Raptor codes encoder based on operation lists for known source block lengths. For a Raptor codes application that can frequently use one or several fixed source block lengths (i.e., the number of source symbols in a source block), we could produce the corresponding operation lists in advance and use them to generate the encoding symbols more efficiently. We first introduce the basic architecture of the proposed Raptor encoder, and then describe the details about how to generate operation lists and Raptor intermediate symbols. The simulation results show that our encoder is at least two times faster than the conventional Raptor codes encoder which is adopted by 3GPP and DVB-H. Besides, the reduction on CPU utilization for a real Raptor-based streaming server is described, which is from 11.59 % to 53.41 %, depending on the employed source block length and symbol size.

Efficient Common Prefix Search on Encrypted Data as an Additional Service on the Top of the Storage Providers

Company data are very often outsourced to cloud service providers in order to lower costs of maintaining hardware. If the outsourced data are to be kept secure from a third party, the connection between the cloud service provider and the company could be secured by a protocol similar to SSL. This, however, requires that the data is stored at the cloud service provider in plaintext form, meaning the company has to trust the cloud service provider and its administrators in order to perform search on the outsourced data. Alternatively, the data themselves could be encrypted, however, the outputs of typical cryptographic algorithms are not amenable to search. For example, if a client wishes to retrieve only documents containing certain words, it was not previously known how to let the data storage server perform the search and answer the query without loss of data confidentiality. By the advantage of our cryptography scheme a query generated at the client-side, is transformed into a representation so that it can be evaluated directly on encrypted data at the could storage server. The results might be processed by the client after decryption to determine the final answers. Additionally, we introduce an efficient common prefix keyword search which makes the scheme more tolerant of minor typos and format inconsistencies when exact keyword matching fails.

A new business model in Pay-TV broadcasting systems and its conditional access system

Recently, the Pay-TV broadcasting system becomes one of the popular applications because of the advance of modern network technique. The conditional access system is the essential function to provide the channel protection in Pay-TV broadcasting system. It ensures that only the authorized subscribers can precisely receive the TV program and the service provider can charge the subscribers according to their subscription. Several conditional access systems have been proposed for different business models such as pay-per-channel, pay-per-view, and flexible pay-per-channel. In this paper, we define a new business model named Flexible Pay-Per-Group and design a conditional access system for it. Compared with the previous works, subscribers in Flexible Pay-Per-Group still have sufficient flexibility. Besides, through our analysis and evaluation, the proposed conditional access system is efficient. Consequently, it can be applied on a large scale Pay-TV system with lots of subscribers and channels.

Accelerating Raptor Code Decoding Using Group Parameters for IPTV Service Delivery

Cloud computing has been recognized as an important advance for virtualizing computing hardware, distributed computing middleware, and communication networks. For simplifying the network OA&M (Operation, Administration, and Management) tasks of customers, a CaaS (Communications-as-a-Service) operator can provide virtual communication channels tailored for delivering various services inside a communication cloud, such as VoIP, video conferencing and IPTV. For improving the video quality of broadband IPTV services, Raptor code has been adopted in various broadband IPTV systems. In this paper, we propose a systematic Raptor code decoder based on the group parameters for a group of encoding symbols. For a Raptor code application that can frequently use one or several fixed block lengths (i.e., the number of source symbols in a source block) such as IPTV, we could produce the corresponding group parameters in advance and then the proposed decoder can use them to decode the received encoding symbols more efficiently. For the IPTV delivery scenario over a communication cloud based on DSL (Digital Subscriber Line) access networks, the simulation results show that our decoder is faster than the conventional Raptor code decoder which is adopted by DVB and 3GPP specifications.