Zhiguo Wan

HASBE: A Hierarchical Attribute-Based Solution for Flexible and Scalable Access Control in Cloud Computing

Cloud computing has emerged as one of the most influential paradigms in the IT industry in recent years. Since this new computing technology requires users to entrust their valuable data to cloud providers, there have been increasing security and privacy concerns on outsourced data. Several schemes employing attribute-based encryption (ABE) have been proposed for access control of outsourced data in cloud computing; however, most of them suffer from inflexibility in implementing complex access control policies. In order to realize scalable, flexible, and fine-grained access control of outsourced data in cloud computing, in this paper, we propose hierarchical attribute-set-based encryption (HASBE) by extending ciphertext-policy attribute-set-based encryption (ASBE) with a hierarchical structure of users. The proposed scheme not only achieves scalability due to its hierarchical structure, but also inherits flexibility and fine-grained access control in supporting compound attributes of ASBE. In addition, HASBE employs multiple value assignments for access expiration time to deal with user revocation more efficiently than existing schemes. We formally prove the security of HASBE based on security of the ciphertext-policy attribute-based encryption (CP-ABE) scheme by Bethencourt and analyze its performance and computational complexity. We implement our scheme and show that it is both efficient and flexible in dealing with access control for outsourced data in cloud computing with comprehensive experiments.

Anonymous secure routing in mobile ad-hoc networks

Although there are a large number of papers on secure routing in mobile ad-hoc networks, only a few consider the anonymity issue. We define more strict requirements on the anonymity and security properties of the routing protocol, and notice that previous research works only provide weak location privacy and route anonymity, and are vulnerable to specific attacks. Therefore, we propose the anonymous secure routing (ASR) protocol that can provide additional properties on anonymity, i.e. identity anonymity and strong location privacy, and at the same time ensure the security of discovered routes against various passive and active attacks. Detailed analysis shows that ASR can achieve both anonymity and security properties, as defined in the requirements, of the routing protocol in mobile ad-hoc networks.

Privacy-Aware Attribute-Based Encryption with User Accountability

As a new public key primitive, attribute-based encryption (ABE) is envisioned to be a promising tool for implementing fine-grained access control. To further address the concern of user access privacy, privacy-aware ABE schemes are being developed to achieve hidden access policy recently. For the purpose of secure access control, there is, however, still one critical functionality missing in the existing ABE schemes, which is user accountability. Currently, no ABE scheme can completely prevent the problem of illegal key sharing among users. In this paper, we tackle this problem by firstly proposing the notion of accountable, anonymous, and ciphertext-policy ABE (CP-A3BE, in short) and then giving out a concrete construction. We start by improving the state-of-the-art of anonymous CP-ABE to obtain shorter public parameters and ciphertext length. In the proposed CP-A3BE construction, user accountability can be achieved in black-box model by embedding additional user-specific information into the attribute private key issued to that user, while still maintaining hidden access policy. The proposed constructions are provably secure.

Highly reliable trust establishment scheme in ad hoc networks

Securing ad hoc networks in a fully self-organized way is effective and light-weight, but fails to accomplish trust initialization in many trust deficient scenarios. To overcome this problem, this paper aims at building well established trust relationships in ad hoc networks without relying on any pre-defined assumption. We propose a probabilistic solution based on distributed trust model. A secret dealer is introduced only in the system bootstrapping phase to complement the assumption in trust initialization. With it, much shorter and more robust trust chains are able to be constructed with high probability. A fully self-organized trust establishment approach is then adopted to conform to the dynamic membership changes. The simulation results on both static and dynamic performances show that our scheme is highly resilient to dynamic membership changing and scales well. The lack of initial trust establishment mechanisms in most higher level security solutions (e.g. key management schemes, secure routing protocols) for ad hoc networks makes them benefit from our scheme.

USOR: An Unobservable Secure On-Demand Routing Protocol for Mobile Ad Hoc Networks

Privacy-preserving routing is crucial for some ad hoc networks that require stronger privacy protection. A number of schemes have been proposed to protect privacy in ad hoc networks. However, none of these schemes offer complete unlinkability or unobservability property since data packets and control packets are still linkable and distinguishable in these schemes. In this paper, we define stronger privacy requirements regarding privacy-preserving routing in mobile ad hoc networks. Then we propose an unobservable secure routing scheme USOR to offer complete unlinkability and content unobservability for all types of packets. USOR is efficient as it uses a novel combination of group signature and ID-based encryption for route discovery. Security analysis demonstrates that USOR can well protect user privacy against both inside and outside attackers. We implement USOR on ns2, and evaluate its performance by comparing with AODV and MASK. The simulation results show that USOR not only has satisfactory performance compared to AODV, but also achieves stronger privacy protection than existing schemes like MASK.

Anonymous user communication for privacy protection in wireless metropolitan mesh networks

As a combination of ad hoc networks and wireless local area network (WLAN), the wireless mesh network (WMN) provides a low-cost convenient solution to the last-mile network-connectivity problem. As such, existing route protocols designed to provide security and privacy protection for ad hoc networks are no longer applicable in WMNs. On the other hand, little research has focused on privacy-preserving routing for WMNs. In this paper, we propose two solutions for security and privacy protection in WMNs. The first scheme relies on group signatures, together with user credentials, to deliver security and privacy protection. By enforcing access control using user credentials, the users identity has to be disclosed to mesh routers. To avoid this, our second scheme employs pairwise secrets between any two users to achieve stronger privacy protection. In the second scheme, the user is kept anonymous to mesh routers. Finally, we analyze these two schemes in terms of security, privacy, and performance.

Enhanced Location Privacy Protection of Base Station in Wireless Sensor Networks

Location privacy in wireless sensor networks has gained a wide concern. Particularly, the location privacy of base station requires ultimate protection due to its crucial position in wireless sensor networks. In this paper, we propose an efficient scheme, consisting of anonymous topology discovery and intelligent fake packet injection (IFPI), to protect the location privacy of base station. Anonymous topology discovery eliminates the potential threats against base station within topology discovery period. On the other hand, IFPI enhances privacy protection strength during data transmission period. Under given conditions, comprehensive simulations demonstrate that our scheme significantly improves privacy strength compared with existing strategies.

Cryptanalysis of Two Password-Authenticated Key Exchange Protocols

Password-Authenticated Key Exchange (PAKE) protocols enable two or more parties to use human-memorable passwords for authentication and key exchange. Since the human-memorable passwords are vulnerable to off-line dictionary attacks, PAKE protocols should be very carefully designed to resist dictionary attacks. However, designing PAKE protocols against dictionary attacks proved to be quite tricky. In this paper, we analyze two PAKE protocols and show that they are subject to dictionary attacks. The analyzed protocols are EPA which was proposed in ACISP 2003 and AMP which is a contribution for P1363. Our attack is based on the small factors of the order of a large group \({\mathbb Z_p^*}\) (i.e., the DLP of subgroup attack), by which the secret password can be fully discovered. We intend to emphasize that our attack is valid since the protocols neither select secure parameter p nor check the order of received values for achieving good efficiency.

Anonymous ID-Based Group Key Agreement for Wireless Networks

Popularity of group-oriented applications motivates research on security and privacy protection for group communications. A number of group key agreement protocols exploiting ID-based cryptosystem have been proposed for this objective. Though bearing beneficial features like reduced management cost, private key delegation from ID-based cryptosystem, they have not taken into account privacy issues during group communication. In wireless networks, the privacy problem becomes more crucial and urgent for mobile users due to the open nature of radio media. In this paper, we proposed an anonymous ID- based group key agreement protocol for wireless networks. Based on ID-based cryptosystem, our protocol not only benefits from the desirable features of ID-based cryptosystem, but also provides privacy protection for mobile users. More important, in the proposed protocol, the computation cost for each group member is largely reduced to meet the computation capability restriction of mobile devices.

A secure privacy-preserving roaming protocol based on hierarchical identity-based encryption for mobile networks

Roaming services in wireless networks provide people with preferable flexibility and convenience. However, such advantages should be offered with both security and privacy in mind. With consideration on privacy protection during roaming in wireless networks, we proposed a hierarchical ID-based roaming protocol in this paper. In our scheme, we use a 2-layer hierarchical ID-based cryptosystem in which a trusted party acts as the root authority, each domain server acts as the second-layer authority, and the roaming user is the end user. With the hierarchical ID-based cryptosystem, we can avoid involvement with home network, and keep the roaming the users identity private. Furthermore, not only the root authority is relieved from management of a large amount of private/public key pairs, but the domain servers are free to generate key pairs for their registered users. At the same time, we use hash chains together with ID-based signatures to achieve non-repudiation for service payment.