In the current Internet architecture, application service providers (ASPs) own users' data and social groups information, which made a handful of ASP companies growing bigger and bigger and denied small and medium companies from entering this business. We propose a new architecture, called Application Independent Information Infrastructure (AI3). The design goals of AI3 are: 1) Decoupling users' data from ASPs and users' social relations from ASPs, such that ASPs become independent from users' data and social relations. 2) Open architecture, such that different ASPs can interoperate with each other. This demo is to show a prototype of AI3. The demo has four parts: 1) ASPindependent data management in AI3; 2) ASP-independent management of users' social relations in AI3; 3) inter-domain data transport and user roaming; 4) real-time communications by using AI3. The demo video can be watched at: http://www.cs.cityu.edu.hk/~jia/AI3_DemoVideo.mp4

Data access control is an effective way to ensure the data security in the cloud. However, due to data outsourcing and untrusted cloud servers, the data access control becomes a challenging issue in cloud storage systems. Existing access control schemes are no longer applicable to cloud storage systems, because they either produce multiple encrypted copies of the same data or require a fully trusted cloud server. Ciphertext-Policy Attribute-based Encryption (CP-ABE) is a promising technique for access control of encrypted data. It requires a trusted authority manages all the attributes and distributes keys in the system. In cloud storage systems, there are multiple authorities co-exist and each authority is able to issue attributes independently. However, existing CP-ABE schemes cannot be directly applied to data access control for multi-authority cloud storage systems, due to the inefficiency of decryption and revocation. In this paper, we propose DAC-MACS (Data Access Control for Multi-Authority Cloud Storage), an effective and secure data access control scheme with efficient decryption and revocation. Specifically, we construct a new multi-authority CP-ABE scheme with efficient decryption and also design an efficient attribute revocation method that can achieve both forward security and backward security. The analysis and the simulation results show that our DAC-MACS is highly efficient and provably secure under the security model.

In a WLAN setting, the system throughput may be heavily affected by a small number of low data rate clients due to the packet-fairness property provided by IEEE 802.11 DCF. This is regarded as the performance anomaly problem. Client relay is a technology widely adopted to solve this problem. An important issue of client relay is to decide when a client's traffic should be relayed and who relays it. However, the existing protocols fail to consider the overhead introduced by DCF contentions, resulting in an inaccurate performance analysis and lead to wrong decisions for client relay. In this paper, we focus on the performance analysis for multi-hop relay networks with consideration of contention overhead of relay nodes in IEEE 802.11 DCF protocols. The main work of this paper includes: we consider the contention overhead in the performance analytical model of collaborative relay networks. This model is more accurate than the existing models. We present a throughput analytical model that considers different traffic demands of clients for the traffic pattern of relay networks. Extensive simulations have been done in NS-2. The simulation results show that our algorithm is more accurate and achieves higher relay performance, compared with existing methods.

Data access control is an effective way to ensure data security in the cloud. However, due to data outsourcing and untrusted cloud servers, the data access control becomes a challenging issue in cloud storage systems. Existing access control schemes are no longer applicable to cloud storage systems, because they either produce multiple encrypted copies of the same data or require a fully trusted cloud server. Ciphertext-policy attribute-based encryption (CP-ABE) is a promising technique for access control of encrypted data. However, due to the inefficiency of decryption and revocation, existing CP-ABE schemes cannot be directly applied to construct a data access control scheme for multiauthority cloud storage systems, where users may hold attributes from multiple authorities. In this paper, we propose data access control for multiauthority cloud storage (DAC-MACS), an effective and secure data access control scheme with efficient decryption and revocation. Specifically, we construct a new multiauthority CP-ABE scheme with efficient decryption, and also design an efficient attribute revocation method that can achieve both forward security and backward security. We further propose an extensive data access control scheme (EDAC-MACS), which is secure under weaker security assumptions.

In this paper, we study the data broadcast issue in wireless networks with directional antennas. We are given an Access Point(AP) and a set of clients served by the AP. Our task is to schedule the transmission of AP by using directional antennas such that the total delay for all clients to receive a broadcast packet is minimized. Directional antennas allow transmission energy to be concentrated on a narrow range along a direction, which can significantly increase the data rate of clients. However, there is a difficult issue in using directional antennas for data broadcasting. If the AP transmits the signals through a single lobe, the data rate of the clients covered by this lobe can be high but it takes more number of transmissions to cover all clients. On the other hand, if the AP transmits the signals through multiple lobes, it takes less number of transmissions for all clients to receive the data, but the signal strength decreases and the data rate drops. We study this tradeoff between the number of transmissions and the data rate. We prove that the data broadcasting problem is NP-hard and we propose a two-phase method to solve the problem. In the first phase, we use singlelobes to cover all clients such that the total transmission delay is minimized. In the second phase, we group these single-lobes into a set of multi-lobes. The goal is again to minimize the total transmission delay. The solution for each subproblem is optimal. Simulation results show significant improvements of performance compared with state of the art algorithms.

Threshold User Authentication is widely used to provide distributed authentication service in Wireless Mesh Networks(WMNs). In a (t, n) threshold authentication scheme, secret authentication keys are shared among n mesh authentication servers (MAS) and any t out of n MASs can collaboratively provide the authentication service. The existing threshold authentication methods usually assume that MASs are static in the system. That is, t and n do not change after system initialization. However, in WMNs, MASs often join or leave the network freely. In this paper, we propose a novel threshold key redistribution protocol, aiming to cope with dynamic change of the authentication group. We also discuss the key redistribution protocol that can tolerate compromised MASs in the network.

Due to the packet-fairness property of the 802.11 WLANs, the clients with low rates take longer time to transmit a packet and would reduce the overall network throughput, as well as the per-node throughput of those high data rate clients. We propose a collaborative relay method, which allows high data rate clients to relay traffic for the low data rate clients to improve the network throughput. There are three original contributions made by this paper: 1) we develop a generalized model to analyze multi-hop relay for clients. By using this model, clients that are several hops away from each other may take the advantage of concurrent transmissions. 2) We propose a centralized algorithm to compute multi-hop relay topology for the clients and it can achieve the optimal throughput in our defined model. 3) We propose a distributed multi-hop relay protocol for clients dynamically connected to or disconnected from the network. Simulation results show that our algorithm can improve the throughput up to 42% on average, which is significantly better than the previous work. Up to 75% of the clients in the network use 1-hop or multi-hop relay, instead of connecting to the AP directly, for the performance gain; and up to 39% of the links have the opportunities to transmit concurrently with another link.

There are two widely used interference models to characterize interference in wireless communication, protocol model and physical model. The protocol model simplifies the interference by considering only two concerned communication links (or nodes). It ignores the cumulative interference from other links (or nodes). On the other side, the physical model considers the cumulative interference of the ambiance, but its application is very much limited due to the complexity to compute the physical interference of the whole system. In this paper, we study the AP placement problem in the physical interference model. By assuming a simple scheduling method, we propose a heuristic algorithm aiming to find the placement of minimal number of APs in an indoor region to meet the end users' QoS requirements. From the simulation results, we find that there is a significant difference in performance between the algorithms that use the physical model and the protocol model. It shows that the results obtained from AP placement algorithm in the protocol model are not close to the real situation due to neglect of cumulative interference.