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In recent years, the sharing economy is developing rapidly and has become a popular economic model. For example, sharing platforms such as Airbnb have gradually entered people ’s field of vision and obtained high economic benefits. However, the information managed by such a centralized platform may be used by criminals and people’s privacy may be violated. In order to achieve the goal of decentralization, we propose a blockchain-based house sharing platform. Users can directly conduct transactions on the blockchain by running smart contracts. Our scheme guarantees the anonymity of users through commitment scheme and zero-knowledge technology. In order to deal with the problems that may be encountered in reality, we propose a trusted authority to trace malicious users. In addition, our platform has reputation mechanism to restrict the behavior of users. We analyze its security and performance, and the result shows that it is feasible in reality.

With the location-based services (LBS) booming, the volume of spatial data inevitably explodes. In order to reduce local storage and computational overhead, users tend to outsource data and initiate queries to the cloud. However, sensitive data or queries may be compromised if cloud server has access to raw data and plaintext token. To cope with this problem, searchable encryption for geometric range is applied. Geometric range search has wide applications in many scenarios, especially the circular range search. In this paper, a practical and secure circular range search scheme (PSCS) is proposed to support searching for spatial data in a circular range. With our scheme, a semi-honest cloud server will return data for a given circular range correctly without uncovering index privacy or query privacy. We propose a polynomial split algorithm which can decompose the inner product calculation neatly. Then, we define the security of our PSCS formally and prove that it is secure under same-closeness-pattern chosen-plaintext attacks (CLS-CPA) in theory. In addition, we demonstrate the efficiency and accuracy through analysis and experiments compared with existing schemes.

Searchable Symmetric Encryption(SSE) remains to be one of the hot topics in the field of cloud storage technology. However, malicious servers may return incorrect search results intentionally, which will bring significant security risks to users. Therefore, verifiable searchable encryption emerged. In the meantime, single-keyword query limits the applications of searchable encryption. Accordingly, more expressive searchable encryption schemes are desirable. In this paper, we propose a verifiable conjunctive keyword search scheme based on Cuckoo filter (VCKSCF), which significantly reduces verification and storage overhead. Security analysis indicates that the proposed scheme achieves security in the face of indistinguishability under chosen keyword attack and the unforgeability of proofs and search tokens. Meanwhile, the experimental evaluation demonstrates that it achieves preferable performance in real-world settings.

Attribute-based encryption received widespread attention as soon as it proposes. However, due to its specific characteristics, the attribute-based access control method is not flexible enough in actual operation. In addition, since access authorities are determined according to users' attributes, users sharing the same attributes are difficult to distinguish. Once a malicious user makes illicit gains by their decryption authorities, it is difficult to trace specific users. This paper follows the practical demand to propose a more flexible key-policy attribute-based encryption scheme with black-box traceability. The scheme has a constant number of constant parameters which can be utilized to construct attribute-related parameters flexibly, and the method of traitor tracing in broadcast encryption is introduced to achieve effective malicious user tracing. In addition, the security and feasibility can be proved by the security proofs and performance evaluation in this paper.

Images play an increasingly important role in our lives as carriers of Information. At the same time, personal devices are increasingly unable to store and compute large amounts of images, so it is necessary to outsource to cloud servers. However, this also brings privacy issues, such as personal photos, medical photos, map mapping, etc. In this paper, we present a content-based image retrieval (CBIR) scheme that can be performed on ciphertext images. In order to better represent the Lage, instead of the traditional algorithms such as SIFT and HOG, image features are extracted using fine-tuned convolutional neural networks, and then outsources the encrypted feature vector and ciphertext image to cloud server. Considering the efficiency of the search, this paper uses the k-means algorithm to and local sensitive hash function to build a secure tree index. This paper proposes a new functional encryption of the inner product to calculate the Euclidean distance between the feature vectors to obtain the similarity between the images, and finally return the ciphertext image satisfying the condition to the user. The experimental results show the efficiency of our program, in addition, the paper gives security analysis to prove that our solution can against Chosen-Plaintext Attack (CPA).

Searchable encryption is a cryptographic primitive that allows users to search for keywords on encrypted data. It allows users to search in archives stored on cloud servers. Among searchable encryption schemes, those supporting multiuser settings are more suitable for daily application scenarios and more practical. However, since the cloud server is semi-trusted, the result set returned by the server is undefined, and most existing multi-user searchable encryption schemes rely heavily on trusted third parties to manage user permission. To address these problems, verifiable multi-user searchable encryption schemes with dynamic management of user search permissions, weak trust on trusted third parties and are desirable. In this paper, we propose such a scheme. Our scheme manages user permission and key distribution without a trusted third party. User search permission and user access permission matrices are generated separately to manage user permissions dynamically. In addition, our scheme can verify the result set returned by the cloud server. We also show that our scheme is index and trapdoor indistinguishable under chosen keyword attacks in the random oracle model. Finally, a detailed comparison experiment is made by using the actual document data set, and the results show that our scheme is efficient and practical.

With the increasing popularity of publish-subscribe systems in the cloud environment, it is of great value to implement an efficient and secure searchable and encrypted publishing subscription scheme with dynamic attributes in a cloud environment. In a publish-subscribe system, it is very important that the user's attributes can be dynamically changed. Most existing schemes which combine searchable encryption with attribute base encryption do not take real-time changes to user attributes into account or are inefficient. To address these problems, we propose a revocable publish-subscribe scheme (RPS) using CP-ABE with efficient attribute and user revocation capability for cloud systems. RPS supports multiple publishers and subscribers, and protects data from access of unauthorized users and cloud server. In addition, it also protects the privacy of the subscription policy, privacy of the uploaded data and keywords, and is forward and backward secure.

Cognitive radio network (CRN) enables dynamic spectrum management where spectrum aggregation and sharing have significantly facilitated relieving the supply-demand gap among skyrocketing number of mobile devices. Secondary users (SUs) can collaboratively detect and exploit the available spectrums of primary users (PUs) from different locations. Unfortunately, it has brought a series of security threats leaking user's location privacy to unauthorized entities. The existing work either had privacy breaches or depended on computationally-intensive public key homomorphic encryption loading intolerably high complexity on resource-constrained SUs. To well address these issues, in this paper, a lightweight privacy-preserving spectrum aggregation and auction scheme PPSAS is proposed in CRNs without leveraging public key homomorphic encryption. Firstly, a new primitive of efficient privacy preserving multiparty data aggregation protocol PPMDA is proposed based on any one-way trapdoor permutation. Then based on PPMDA, an efficient privacy preserving spectrum aggregation scheme PPSRA and spectrum auction scheme PPSSA are respectively devised to constitute our proposed PPSAS. Especially, a decentralized PPMDA is extended to resist collusion attack and a secure extended outsourced stable complete marriage matching protocol is given to flexibly realize SU/auctioneer optimization. Finally, formal security proof and extensive simulations demonstrate that our proposed PPSAS well protects the SUs' location privacy against collusion attacks and possesses the advantages over the sate-of-the-art in terms of auctioneer's revenue, SUs' satisfaction, computational and communication overhead.

In our previous work, we explored the possibility of applying machine learning technique to graph partition. We use some metrics to describe the graph, rank the execution time of some graph algorithm and feed them into the machine learning models. We proved that decision tree and KNN and good models of this problem. In the paper, we go on to investigate more metrics to describe the graph after partitioning. We found that AverageDegreeNotCut is also an important metric. We improve the precision score of original machine learning models by 4.9 percent.

In this paper, we propose a revocable public key encryption with authorized keyword search (RPEAKS) scheme. In RPEAKS, data and keywords are encrypted with one public key, users without corresponding private key need authorization from the manager if they want to search through the ciphertexts. The manager authorizes users by distributing authorized tokens to them and is able to revoke a user’s search right when needed. Then we present a concrete RPEAKS construction, which is featured with constant size tokens and efficient revocation. Security analysis shows that the scheme is semantically secure against chosen keyword attack and is trapdoor unforgeability.

Autonomous vehicles are expected to be a disruptive technology that has the potential to revolutionize the human mobility. However, the recent research progress on intra-vehicle network (e.g., the revealing of a series of security vulnerabilities of CAN design) has demonstrated that the security issue still represents one of the major challenges of future self-driving cars. In this study, we propose a novel edge based anomaly detection system, coined VeAnDe, which exploits edge based sensor data fusion to identify the anomaly events. VeAnDe analyzes pair-wise correlations between different intra-vehicle sensors, and utilizes these correlations to examine whether an anomaly has occurred within the vehicle. More specifically, the pair-wise correlations are organized as ring architecture to reduce the computation overhead. Furthermore, the major components of VeAnDe are embedded in edge computing devices, which enables VeAnDe to be more efficient and privacy-preserving. We evaluate the performance of VeAnDe under different scenarios, and our experimental results demonstrate its feasibility and efficiency.

The highly development of Internet and cloud computing technology makes it possible to share computing power, storage and data. Cloud computing makes users with limited computing resources be able to carry out large computational tasks with the help of cloud. but security is a major concern that hinders the widespread use of outsourcing computing. We focus on outsourcing large matrix multiplication in this paper. Firstly, we exploit Chinese Remainder Theorem(CRT) to construct a large matrix multiplication outsourcing protocol which is highly efficient in the malicious cloud model. Then formal security proof and extensive performance evaluation show that our protocol achieves a higher security level i.e., information-theoretic security for input privacy and adaptive chosen ciphertext attack (CCA2) security for output privacy). Compared with previous works, users in the proposed protocol are able to verify the results received from the cloud with tiny error rate.

Searchable encryption has emerged in order to maintain the balance between data privacy and convenience of keyword search. In 2017, Huang et al. introduced the notion of inside keyword guessing attack (IKGA), which means the inside adversary could try out the keyword specified by a given trapdoor by guessing offline and proposed a scheme called Public-key Authenticated Encryption with Keyword Search (HQ-PAEKS) to solve this problem. However, the search complexity of HQ-PAEKS is linear to the total number of the encrypted indexes and may be not in a position to meet the demand of practical application. This paper combines the idea of Public-key Authenticated Encryption with hidden structure and proposes a practical scheme called Public-key Authenticated Encryption with Fast Keyword Search (PAEFKS), in which the search complexity for the cloud server presents linear relation with the number of the encrypted indexes matching the trapdoor sent from the data user. In addition, it gives security analysis to show that the scheme could protect index and keyword privacy well and experiments on real-world data sets show that the scheme indeed reduces the overhead on keyword search computation in the cloud.

With the increasing popularity of cloud computing, a huge amount of documents are stored on the cloud for reduced management cost and ease of access. Although data encryption offers help in some ways, it leaves other privacy concerns behind when users want to share documents with others. Otherwise, the users often share documents in the ABE settings in order to support broadcasting, error-tolerace, etc, however, the Attribute Authority will bear mounts of computations. In this paper, we combine the secure outsourced ABE systems with the keywords search while supporting multi-keyword search and search result ranking, which let the data owner securely uploads the data to a third organization and the data user can search over the ciphertext with multi-keywords and decrypt it without much computation with the help of a third server.

Position-based cryptography has attracted lots of researchers' attentions. In mobile Internet, there are lots of position based security applications. For the first time, one new conception, position-based proxy signcryption is proposed. Based on a secure positioning protocol, one model of position-based proxy signcryption is proposed. In the model, positioning protocol is tightly bound to proxy signcryption, not loosely. Further, we propose one concrete position-based proxy signcryption scheme, its correctness is proved, and its security is also analyzed. As far as we know, it is the first position-based proxy signcryption scheme.

Verifiable outsourced computation enables a computational resource-constrained mobile device to outsource the computation of a function F on multiple inputs x 1 , …, x n to the cloud that is generally assumed to possess abundant powers. The most existing work depends on Yao's Garbled Circuit and fully homomorphic encryptions that took considerable computational overhead on weak clients. In this paper, a more efficient verifiable outsourced computation of encrypted data EVOC supporting any functions from any one-way trapdoor function is proposed, based on our newly-devised privacy preserving data aggregation supporting both addition and multiplication operations without exploiting fully homomorphic encryption (FHE). It solves the open problem suggested by Gennaro et al. that how to devise a verifiable computation scheme that used a more efficient primitive than FHE. Finally, the formal security proof and extensive efficiency evaluations demonstrate our proposed EVOC satisfies the target security and privacy requirements and far outperforms the state-of-the-art in terms of computational and communication complexity.

Smart Grid technologies are ever-increasingly being adopted by nations and governments, primarily for a huge technological advancement in the areas of power management and information and communications. The smart meters deployed in a household can monitor electricity usage in real-time, and aggregate the data for further analysis and control; however, the existing solutions mainly depend on Paillier's additive homomorphic encryptions, which are of high computational complexity. This inefficiency makes them impracticable in smart grid, which embraces thousands of users and requires frequent data aggregation. In this paper, we propose a privacy-preserving aggregation framework, followed by a concrete construction using Elgamal encryption, which is secure under chosen plaintext attack (CPA) but not chosen ciphertext attack (CCA). Then, we further extend the concrete construction into a CCA-secure counterpart. In addition to efficient data aggregation, the proposed scheme can protect the user's meter data from sophisticated attacks, which are sponsored by the community gateway and the users. The formal security proof and performance evaluations illustrate the efficiency and the practicability of our scheme as well as its strong security.

Rumor blocking and Sybil Attack are regarded as two main security threats in online social networks. The existing work on rumor blocking mainly considers how to minimize the number of protectors used to protect bridge ends. In this study, our experiments based on the Twitter data set show that the existence of the sybil users will dramatically reduce the effectiveness of the rumor blocking by 30%. Motivated by this, we propose a novel sybil-aware least cost rumor blocking framework which jointly considering how to minimize the impact sybil attacks on rumor blocking and optimize the rumor blocking effectiveness. The proposed SLCRB algorithm is well demonstrated by extensive simulations and discussions.

Personal profiles usually contain sensitive information of people, while the emerging requirement of profile matching in mobile social networks may occasionally leak the sensitive information and hence violate people' privacy. In this paper we propose a user self-controllable profile matching protocol in privacy-preserving mobile social networks. By using our protocol, users can customize the matching metrics to involve their own matching preference and to make the matching results more precise. In addition, detailed security analysis demonstrates that our protocol can protect the privacy of both users' profile item names and profile item values during the matching process. Moreover, extensive performance evaluation are conducted to illustrate that our protocol is more efficient than a relevant protocol in terms of computation and communication overhead, especially when the maximum value of profile item is large.

Position-based cryptography has attracted lots of researchers' attention. In the mobile Internet, there are many position-based security applications. For the first time, one new conception-proxy multi-signature binding positioning protocols, is proposed. Based on one secure positioning protocol, one model of the proxy multi-signature binding positioning protocols is proposed. In the model, positioning protocols are bound to proxy multi-signature tightly, not loosely. Further, we propose one scheme of proxy multi-signature binding positioning protocols. As far as we know, it is the first scheme of proxy multi-signature binding positioning protocols.

Cognitive Radio Network (CRN) is regarded as a promising way to address the increasing demand for wireless channel resources. It solves the channel resource shortage problem by allowing a Secondary User (SU) to access the channel of a Primary User (PU) when the channel is not occupied by the PU. The latest FCC's rule in May 2012 enforces database-driven CRNs, in which an SU queries a database to obtain spectrum availability information by submitting a location based query. However, one concern about database-driven CRNs is that the queries sent by SUs will inevitably leak the location information. In this study, we identify a new kind of attack against location privacy of database-drive CRNs. Instead of directly learning the SUs' locations from their queries, our discovered attacks can infer an SU's location through his used channels. We propose Spectrum Utilization based Location Inferring Algorithm that enables the attacker to geo-locate an SU. To thwart location privacy leaking from query process, we propose a novel Private Spectrum Availability Information Retrieval scheme that utilizes a blind factor to hide the location of the SU. To defend against the discovered attack, we propose a novel prediction based Private Channel Utilization protocol that reduces the possibilities of location privacy leaking by choosing the most stable channels. We implement our discovered attack and proposed scheme on the data extracted from Google Earth Coverage Maps released by FCC. Experiment results show that the proposed protocols can significantly improve the location privacy.

In this paper, we propose a two-level path authentication protocol for object genuineness verification in RFID-based supply chain and EPCglobal Network. In our solution, a tag's path in a supply chain can be generated dynamically, where each reader in the path can verify the validation of the path using its own private key. Our solution has a few promising properties, including dynamic path generation, distributed authentication, and scalability. In comparison, the previous path authentication solution for RFID tags is focused on static path generation and centralized control. The efficiency of our path authentication protocol is enhanced significantly by dividing a whole path into multiple segments according to organization structures. The security and privacy of our protocol are established based on two cryptographic primitives, hierarchical identity-based encryption and batch verification signature.

In this paper, we propose an event-aided packet forwarding (EPF) protocol, which enables patients to efficiently communicate with each other in privacy-preserving Mobile Healthcare Social Networks (MHSNs). Since patients with common illnesses often attend the same related activities, EPF makes use of these activities in forwarding illness-related messages to the target patients so that it can achieve high target patients coverage ratio. In addition, EPF also adopts predicate encryption to guarantee patient privacy and message confidentiality. Through security analysis, we demonstrate that EPF can effectively resist various attacks launched by adversaries, and ensure patient identity and illness privacy. Extensive simulations are also conducted to evaluate the performance of EPF in terms of average target patients coverage ratio, average number of packet copies, and average packet delay.

Delay/Disruption tolerant networks (DTNs) are self-organized wireless networks, where end-to-end network connectivity is not available and the data forwarding relies on the assumption that the intermediate nodes are ready to ``store, carry and forward'' messages in an opportunistic way. This assumption can be easily violated by the selfish nodes which may be unwilling to use their precious resources by serving as relays. Due to the unique network characteristics, incentive issue is extraordinarily challenging in DTNs. To tackle this issue, in this paper, we propose MobiGame, a user-centric reputation based incentive protocol for DTNs, which allows a node to manage its reputation evidence. For the fairness requirement, we define a game-theoretic framework to design reasonable costs and reward parameters in the MobiGame's bundle forwarding, which leads to a Perfect Bayesian Equilibrium. Performance simulations are given to demonstrate the security, effectiveness and efficiency.

In distributed collaborative networks such as peer-to-peer systems and wireless ad hoc networks, secure communications, information sharing and dissemination heavily depend on effective trust management. Recently, trust based encryption (TBE) has been proposed to deal with secure information sharing and dissemination for such networks. Unfortunately, the previously proposed schemes are not efficient in terms of communications overhead. In this paper, we provide a trust based encryption schemes which can significantly improve the communication overhead. The proposed scheme is based on a recently proposed revocable identity based encryption technique which can reduce the communication overhead at the central trust authority from the linear order of the number of the users in the network to the linear order of the number of the revoked users.

Several group signature schemes have been proposed up to date. However, in order for the entire group signature concepts to become practical and credible, the problems of secure and efficient procedures of such schemes must be addressed. At the same time, allowing group members to join or to leave from the group dynamically is another urgent requirements for group signature concepts to become really practical. In this paper, we construct the first group signature scheme with group member revocation function from conic. Due to the properties of conic, the proposed scheme is of great efficiency.

In this paper, for the first time, we put forward the concepts and security requirements of electronic resume firstly. Then a concrete implementation of efficient and secure electronic resume scheme using smart card is also presented. Identity-based public key systems and message recovery signature schemes are adopted as building blocks in our scheme. No certificate is required to authenticate the electronic resume, and the job seeker's working experiences is unnecessary to be stored independently, since it can be recovered when the validity of the resume is checked. Our scheme is efficient and suitable for smart cards or similar devices, which are readily available but are constrained in terms of processing power and storage space.

This paper presents the first multi-use unidirectional proxy re-encryption scheme proven-secure against chosenciphertext attacks and collusion attacks in the standard model. Although our proposal features a linear ciphertext size and decryption time in the number of translations, we emphasize that it is the first multi-use and unidirectional realization of the primitive satisfying the chosen-ciphertext security and collusion resistance. The proposal gives an answer to the problem proposed by Canetti and Hohenberger at ACM CCS 2007.

Mobile communication technologies have been widely utilized in daily lives, many low-computing-power and weakly-structured-storage devices have emerged, such as PDA, cell phones and smart cards, etc. How to solve the security problems in such devices has become a key problem in secure mobile communication. In this paper, we would like to propose an efficient signature-encryption scheme. The security of the signature part is not loosely related to Discrete Logarithm Problem (DLP) assumption as most of the traditional schemes but tightly related to the trapdoor permutation (large integer factoring problem (LIFP)) in the Random Oracle Models. Different from the existing solutions, our scheme introduces a trusted agent of the receiver who can filter the rubbish messages beforehand. Thus, with high efficiency in computation and storage, it is particularly suitable for the above mobile devices with severely constrained resources and can satisfy the security requirements of mobile computations.

XSS (Cross-Site Scripting) is a major security threat for web applications. Due to lack of source code of web application, fuzz technique has become a popular approach to discover XSS in web application except Webmail. This paper proposes a Webmail XSS fuzzer called L-WMxD (Lexical based Webmail XSS Discoverer). L-WMxD , which works on a lexical based mutation engine, is an active defense system to discover XSS before the Webmail application is online for service. The engine is initialized by normal JavaScript code called seed. Then, rules are applied to the sensitive strings in the seed which are picked out through a lexical parser. After that, the mutation engine issues multiple test cases. Newly-generated test cases are used for XSS test. Two prototype tools are realized by us to send the newly-generated test cases to various Webmail servers to discover XSS vulnerability. Experimental results of L-WMxD are quite encouraging. We have run L-WMxD over 26 real-world Webmail applications and found vulnerabilities in 21 Webmail services, including some of the most widely used Yahoo!Mail, Mirapoint Webmail and ORACLE' Collaboration Suite Mail.

To enhance the security of mobile cloud users, a few proposals have been presented recently. However we argue that most of them are not suitable for mobile cloud where mobile users might join or leave the mobile networks arbitrarily. In this paper, we design a secure mobile user-based data service mechanism (SDSM) to provide confidentiality and fine-grained access control for data stored in the cloud. This mechanism enables the mobile users to enjoy a secure outsourced data services at a minimized security management overhead. The core idea of SDSM is that SDSM outsources not only the data but also the security management to the mobile cloud in a trust way. Our analysis shows that the proposed mechanism has many advantages over the existing traditional methods such as lower overhead and convenient update, which could better cater the requirements in mobile cloud computing scenarios.

Bundle Authentication is a critical security service in Delay Tolerant Networks (DTNs) that ensures authenticity and integrity of bundles during multi-hop transmissions. Public key signatures, which have been suggested in existing bundle security protocol specification, achieve bundle authentication at the cost of an increased computational, transmission overhead and a higher energy consumption, which is not desirable for energy-constrained DTNs. On the other hand, the unique ``store-carry-and-forward'' transmission characteristic of DTNs implies that bundles from distinct/common senders can be buffered opportunistically at some common intermediate nodes. This ``buffering'' characteristic distinguishes DTN from any other traditional wireless networks, for which an intermediate cache is not supported. To exploit such a buffering characteristic, in this paper, we propose an Opportunistic Batch Bundle Authentication Scheme (OBBA) to achieve efficient bundle authentication. The proposed scheme adopts batch verification techniques, allowing a computational overhead to be bounded by the number of opportunistic contacts instead of the number of messages. Furthermore, we introduce a novel concept of a fragment authentication tree to minimize communication cost by choosing an optimal tree height. Finally, we implement OBBA in a specific DTN scenario setting: pocket-switched networks on campus. The simulation results in terms of computation time, transmission overhead and power consumption are given to demonstrate the efficiency and effectiveness of the proposed schemes.

Nowadays, most proxy signature schemes are based on the difficulty of DLP (Discrete Logarithm Problem) or ECDLP (Elliptical Curve Discrete Logarithm Problem). As though many proxy signature schemes based on DLP or ECDLP have been proposed, it makes us discouraged that some disadvantages can be found after a new or modified proxy signature scheme was designed after short time. How to solve the question? How to design secure and valid proxy signature scheme? How to prove them secure? Now, it is too difficult for us to prove one scheme secure, but if we can have some principles to conform to when designing some proxy signature schemes based on DLP or ECDLP, it will be helpful. It will be able to make the scheme designer to make few mistakes, that's to say, by these principles, they can judge their schemes meet basic secure conditions. If designers don't conform to these principles, it can easily be seen that their schemes are definitely insecure. It is all known by us that until now there are not these principles in the real life. By some hints from some attacks, especially forgery attacks, it seems to us that we have found three basic principles which should be conformed to when proxy signature schemes are proposed. The first principle is that the existent forms of public parameters in proxy signatures in the proxy signature verification congruence make a key role on the security property of unforgeability. The second principle is that any public parameter in the proxy signature can't lonely exist in the proxy signature verification congruence in the form of bases or exponents. The third principle is that any public parameter in the proxy signature should exist in the proxy signature verification equation in the form of not only exponents and bases, but also hashes. In addition, some examples are given.

Private information retrieval enables the sensitive data to be obtained only if the data authorizers allow the data receivers to access to the data. Sometimes the owners are of a group and there is no need for all members to authorize the receivers. Moreover, the right to authorize could be unequal for different authorizers in the group.

In a (t, n) threshold proxy signature scheme, one original signer delegates a group of n proxy signers to sign on behalf of the original signer. When the proxy signature is created, at least t proxy signers cooperate to produce valid proxy signatures and any less than t proxy signers can't cooperatively generate valid proxy signatures. Self-certified public key systems have attracted more and more attention because of its advantages. In 2005, Hsu and Wu designed a self-certified threshold proxy signature scheme with message recovery, nonrepudiation and traceability, which is based on Hsu et al.'s self-certified public key system. Park et al. showed that Hsu and Wu's self-certified threshold proxy signature scheme is insecure against the malicious original signer in 2006. That is, Hsu and Wu's scheme suffers from the cheat attack, where a malicious original signer can cheat CA into extracting a proxy signing key of a proxy signer. We analyzed Park et al's security analysis for Hsu and Wu's scheme and pointed out that the cheat attack proposed by Park et al. can't succeed. In one hand, in self-certified public system, users cannot freely change their private or public keys. If users want to change their private or public keys, CA has some corresponding strategy to limit users' behaviors. In the other hand, if some disagreement about the forged threshold proxy signature occurs, there are two solutions to deal with it. One solution depends on the help of CA and the other solution relies on the help of the delegated proxy signer.

The well-known method for a group key exchange (GKE) protocol to be against insider attack is to make use of signatures. However, using signatures considerably degrades the performance of the GKE protocol. In this paper, we propose a new method to resist insider attack. The underlying tool of our method is a two-party authenticated key exchange (AKE) protocol, which can be used to authenticate all other participants' session identifiers instead of using signatures. Based on the two-party AKE protocol, we propose an efficient insider-resistant GKE protocol without signatures. We show that our proposal is provably secure against insider attack if the underlying two-party AKE protocol is secure.

The focus of this paper is to design an efficient Certificateless Threshold Signature scheme (CLTHS) for data report authentication in mobile ad-hoc network, by which relatively small subsets of very large groups can report data that is aggregated and ``certified" by means of a signature. Examples include vehicular networks where cars report traffic conditions, sensor networks that report aggregate data such as temperature or radiation levels, military devices transmitting information to be reported to various commands, and more. We first define the security notion for Certificateless Threshold Signature. Different from the adversarial model defined by Wang et al., our definition considers Type I and Type II adversary separately. At the same time, we develop the simulatability and relationship between certificateless threshold signature and the underlying certificateless signature. We also propose the first CLTHS scheme which is proved existentially unforgeable against adaptively chosen message attack without random oracles. Compared with the previous scheme, our scheme is much more efficient.

The focus of this paper is to design an efficient and secure solution addressing the key escrow problem in proxy re-signature schemes, i.e., the proxy knows the user's private key, which damages the essential requirement - "non-repudiation" property of proxy re-signature schemes. In this paper, we first define the security model for threshold proxy re-signature scheme, and then propose two threshold proxy re-signature schemes based on Ateniese's (see ACM CCS, p.310-319, 2005) and Shao Jun's (see Progress in Cryptology - INDOCRYPT 2007, vol.4859 of LNCS, p.197-209, 2007) approach. To our knowledge, there is no threshold proxy re-signature scheme that has been formally presented yet.

To achieve secure group communications, it is critical to develop a secure group key management strategy to guarantee security of the group keys. In this paper, based on the forward security and secret sharing techniques, we propose a new dynamic group key management scheme to minimize the rekeying cost. The forward security technique reduces the rekeying operations in joining event, while the secret sharing technique ensures the scalability in leaving event. In addition, the proposed scheme can provide anonymous authentication as well as forward and backward confidentiality. Theoretical analysis also confirms the efficiency of the proposed scheme.

In this paper, we discuss identity-based encryption in multiple PKG environment. We formulate the security notions for multi-receiver multi-PKG identity-based encryption (IBE) and present an efficient multi-receiver IBE scheme which is proven secure against a new hard problem called N-xDBDH in random oracle model.

In this paper, we present a novel anonymous secure routing protocol for mobile ad hoc networks (MANETs). The proposed protocol not only provides anonymity from all the intermediate nodes, but also integrates the authenticated key exchange mechanisms into the routing algorithm design. Furthermore, a new attack on anonymous services, called snare attack, is introduced, where a compromised node lures a very important node (VIN) into communicating with him and traces back to the VIN by following the route path. An adversary can then snare the VIN and launch decapitation strike on the VIN. Finally, we present a novel DECOY mechanism as a countermeasure to enhance anonymity of VINs and defeat snare attack.

In a (t,n) threshold proxy signature scheme, an original signer delegates a group of n proxy signers to sign messages on behalf of him or her. When the proxy signature is created, t or more proxy signers cooperate to generate valid proxy signatures and any less than t proxy signers can't cooperatively produce valid proxy signatures. In 2003, Hwang et al. proposed a practical threshold proxy signature scheme (HLL-scheme) which is based on RSA crypto system for the first time. In 2004, Wang et al. had provided some comments on HLL-scheme. They showed that some mistakes of equations had made HLL-scheme become insecure. Moreover, in 2005, Kuo and Chen also showed two security weaknesses in Hwang et al.'s scheme: one is similar to RSA reblocking problem and the other is that the value of Li is not clearly defined. In addition, to overcome the second shortcoming of HLL-scheme, Kuo and Chen also provided a modified threshold proxy signature scheme (KC-scheme) based on HLL-scheme. By observation, we find that KC-scheme cannot still work. In other words, in KC-scheme, the value of Li cannot still be worked out, as makes KC-scheme not workable. To design a workable threshold proxy signature scheme, based on KC-scheme, an improved scheme is proposed

User authentication is essential in service-oriented communication networks to identify and reject any unauthorized network access. The state-of-the-art practice in securing wireless networks is based on the technique of authentication, authorization and accounting (AAA) framework where an AAA server is adopted to authenticate mobile users (MUs), handle authorization requests, and collect accounting data. However, the traditional AAA framework is by way of a single authentication server, and cannot tolerate AAA server failure due to various malicious attacks such as denial-of-service (DoS) attack, or any other failure event such that the authentication server is compromised due to misuse, misconfiguration and malicious access, etc. Thus, a more resilient approach is to adopt multiple authentication servers, where any authentication request is handled by more than one authentication servers in order to resist any compromise event of an authentication server. To meet this design objective, we introduce a novel compromise-resilient authentication system based on (t, n) threshold signature technique. With the proposed system, only t or more out of n authentication servers can cooperatively allow a MU to have network access, and any t-1 or less cannot. Case study of reliability analysis is conducted to demonstrate the effectiveness of the system. The proposed authentication system is expected to particularly contribute to wireless mesh networking (WMN) in metropolitan areas where thousands of nodes may coexist and are managed under a single control plane such that duplicated AAA servers are necessary.