As an important security property of cloud storage, data integrity has not been sufficiently studied under the multi-writer model, where a group of users work on shared files collaboratively and any group member can update the data by modification, insertion, and deletion operations. Existing works under such multi-writer model would bring large storage cost to the third-party verifiers. Furthermore, to the best of our knowledge, none of the existing works for shared files supports fully dynamic operations, which implies that users cannot freely perform the update operations. In this paper, we propose the first public auditing scheme for shared data that supports fully dynamic operations and achieves constant storage cost for the verifiers. Our scheme, named PRAYS, is boosted by a new paradigm for remote data integrity checking. To implement the new paradigm, we proposed a specially designed authenticated structure, called blockless Merkle tree, and a novel cryptographic primitive, called permission-based signature. Extensive evaluation demonstrates that PRAYS is as efficient as the existing less-functional solutions. We believe that PRAYS is an important step towards designing practical multi-writer cloud storage systems.

Motivated by privacy preservation requirements for outsourced data, keyword searches over encrypted cloud data have become a hot topic. Compared to single-keyword exact searches, multi-keyword fuzzy search schemes attract more attention because of their improvements in search accuracy, typo tolerance, and user experience in general. However, existing multi-keyword fuzzy search solutions are not sufficiently efficient when the file set in the cloud is large. To address this, we propose an Efficient Leakage-resilient Multi-keyword Fuzzy Search (EliMFS) framework over encrypted cloud data. In this framework, a novel two-stage index structure is exploited to ensure that search time is independent of file set size. The multi-keyword fuzzy search function is achieved through a delicate design based on the Gram Counting Order, the Bloom filter, and the Locality-Sensitive Hashing. Furthermore, considering the leakages caused by the two-stage index structure, we propose two specific schemes to resist these potential attacks in different threat models. Extensive analysis and experiments show that our schemes are highly efficient and leakage-resilient.

In recent years, real-world attacks against PKI take place frequently. For example, malicious domains' certificates issued by compromised CAs are widespread, and revoked certificates are still trusted by clients. In spite of a lot of research to improve the security of SSL/TLS connections, there are still some problems unsolved. On one hand, although log-based schemes provided certificate audit service to quickly detect CAs' misbehavior, the security and data consistency of log servers are ignored. On the other hand, revoked certificates checking is neglected due to the incomplete, insecure and inefficient certificate revocation mechanisms. Further, existing revoked certificates checking schemes are centralized which would bring safety bottlenecks. In this paper, we propose a blockchain-based public and efficient audit scheme for TLS connections, which is called Certchain. Specially, we propose a dependability-rank based consensus protocol in our blockchain system and a new data structure to support certificate forward traceability. Furthermore, we present a method that utilizes dual counting bloom filter (DCBF) with eliminating false positives to achieve economic space and efficient query for certificate revocation checking. The security analysis and experimental results demonstrate that CertChain is suitable in practice with moderate overhead.

Location-based service (LBS) has gained increasing popularity recently, but protecting users' privacy in LBS remains challenging. Depending on whether a trusted third party (TTP) is used, existing solutions can be classified into: TTP-based and TTP-free. The former relies on a TTP for user privacy protection, which creates a single-point-failure and is thus impractical in reality. The latter does not require any TTP, but usually introduces redundant point-of-interest (POI) records in query result and thus incurs significant computation and communication costs on the user side, making them unsuitable for resource-constrained mobile devices. In this paper, we propose a novel framework to protect user privacy while ensuring efficiency. Our framework also uses redundant POI records to protect privacy against LBS provider but employs a semi-trusted third party, called proxy, to filter out redundant POI records. To protect privacy against proxy, we design a novel filtering protocol, Blind filter, to allow the proxy to filter out redundant encrypted POI records in a blind way. In comparison with existing solutions, our framework is not only resilient to dual identity attack, but also incurs lower communication and computation overhead. Comprehensive analysis and experiments show that our framework is secure and highly efficient in mobile environments.

Recent real-world attacks against Certification Authorities (CAs) and fraudulently issued certificates arouse the public to rethink the security of public key infrastructure for web-based connections. To distribute the trust of CAs, notaries, as an independent party, are introduced to record certificates, and a client can request an audit proof of certificates from notaries directly. However, there are two challenges. On one hand, existing works consider the security of notaries insufficiently. Due to lack of systematic mutual verification, notaries might bring safety bottlenecks. On the other hand, the service of these works is not sustainable, when any party leaks its private key or fails. In this paper, we propose a Tripartite Public Key Infrastructure (TriPKI), using Certificates Authorities, Integrity Log Servers, and Domain Name Servers, to provide a basis for establishing secure SSL/TLS connections. Specifically, we apply checks-and balances among those three parties in the structure to make them verify mutually, which avoids any single party compromise. Furthermore, we design a collaborative certificate management scheme to provide sustainable services. The security analysis and experiment results demonstrate that our scheme is suitable for practical usage with moderate overhead.

Secure access is one of the fundamental problems in wireless mobile networks. Digital signature is a widely used technique to protect messages' authenticity and nodes' identities. From the practical perspective, to ensure the quality of services in wireless mobile networks, ideally the process of signature verification should introduce minimum delay. Batch cryptography technique is a powerful tool to reduce verification time. However, most of the existing works focus on designing batch verification algorithms for wireless mobile networks without sufficiently considering the impact of invalid signatures, which can lead to verification failures and performance degradation. In this paper, we propose a Batch Identification Game Model (BIGM) in wireless mobile networks, enabling nodes to find invalid signatures with reasonable delay no matter whether the game scenario is complete information or incomplete information. Specifically, we analyze and prove the existence of Nash Equilibriums (NEs) in both scenarios, to select the dominant algorithm for identifying invalid signatures. To optimize the identification algorithm selection, we propose a self-adaptive auto-match protocol which estimates the strategies and states of attackers based on historical information. Comprehensive simulation results in terms of NE reasonability, algorithm selection accuracy, and identification delay are provided to demonstrate that BIGM can identify invalid signatures more efficiently than existing algorithms.

Abstract With the dramatic development of social network applications, such as the Facebook, Twitter, and MySpace, privacy‐preserving problem is getting increasingly concerned. Apart from node information, researchers have found that structure information can also leak data providers' privacy, especially in weighted social networks. However, most of the existing private‐preserving schemes focus on a single aspect. The comprehensive consideration introduces two challenges. On one hand, the different anonymity demands of node and structure information lead to the collision of different design criteria, which is called as consistency matching problem. On the other hand, the simple combination of existing schemes may introduce large amounts of unnecessary changes, which makes the published information meaningless. Thus, we must find the balance between anonymity demands and changes, which is called as optimization trade‐off problem. In this paper, we propose aγ‐Strawman privacy‐preserving scheme in weighted social networks to solve these challenges. To address consistency matching problem, we propose a greedy algorithm based on a user trade‐off metric. For optimization tradeoff problem, a closeness edge‐editing technology is considered, which can change the private information slightly. Finally, we evaluate our scheme on real‐world datasets, the experimental results show that theγ‐Strawman scheme is efficient. Copyright © 2017 John Wiley & Sons, Ltd.

Routing in Delay-Tolerant Networks (DTNs) remains a challenging problem due to sporadic connectivity and high delays. To deal with this issue, researchers have investigated multi-copy schemes with predicting future contacts. However, most of the previous work has focused on the prediction of future contacts, without sufficiently considering contact times. This paper proposes McRTP, a multi- copy routing protocol with trajectory prediction for social DTNs. Based on estimating the probability distribution of future contact times, McRTP evaluates and selects multiple paths with the highest delivery probability for routing. Also, to control network traffic overhead, we develop a copy count assignment scheme limiting the number of message copies in networks. A simulation study shows that, with the estimation of both contact probability and contact times, and the path selection scheme, our McRTP outperforms traditional DTN multi-copy routing schemes, especially in sparse networks.

Digital signature has been widely employed in wireless mobile networks to ensure the authenticity of messages and identity of nodes. A paramount concern in signature verification is reducing the verification delay to ensure the network QoS. To address this issue, researchers have proposed the batch cryptography technology. However, most of the existing works focus on designing batch verification algorithms without sufficiently considering the impact of invalid signatures. The performance of batch verification could dramatically drop, if there are verification failures caused by invalid signatures. In this paper, we propose a Game-theory-based Batch Identification Model (GBIM) for wireless mobile networks, enabling nodes to find invalid signatures with the optimal delay under heterogeneous and dynamic attack scenarios. Specifically, we design an incomplete information game model between a verifier and its attackers, and prove the existence of Nash Equilibrium, to select the dominant algorithm for identifying invalid signatures. Moreover, we propose an auto-match protocol to optimize the identification algorithm selection, when the attack strategies can be estimated based on history information. Comprehensive simulation results demonstrate that GBIM can identify invalid signatures more efficiently than existing algorithms.

It has been proved that network coding can optimize routing in wireless networks. Thus, in deterministic routing, coding is considered as an important factor for route selection. While the existing deterministic routing solutions detect paths with coding opportunities based on the two-flow coding, little attention has been drawn to the multi-flow situation. Coding multiple flows directly, however, can improve the coding benefit when multiple flows intersect at coding nodes. In this paper, we analyze the challenges of the multi-flow coding, and propose a Greedy Multi-flow-based Coding-aware Routing (MuCAR) protocol in wireless networks. The main idea is to define the decoding policy and the coding condition in the multi-flow environment, and code the multiple intersecting flows in a greedy way. Meanwhile, we discuss the interference issue in the multi-flow coding and its solution. We show that MuCAR can induce competitive performance in terms of increased coding benefit and decreased delay, which is verified by extensive simulations.

Wireless mesh networks are widely applied in many fields such as industrial controlling, environmental monitoring, and military operations. Network coding is promising technology that can improve the performance of wireless mesh networks. In particular, network coding is suitable for wireless mesh networks as the fixed backbone of wireless mesh is usually unlimited energy. However, coding collision is a severe problem affecting network performance. To avoid this, routing should be effectively designed with an optimum combination of coding opportunity and coding validity. In this paper, we propose a Connected Dominating Set (CDS)-based and Flow-oriented Coding-aware Routing (CFCR) mechanism to actively increase potential coding opportunities. Our work provides two major contributions. First, it effectively deals with the coding collision problem of flows by introducing the information conformation process, which effectively decreases the failure rate of decoding. Secondly, our routing process considers the benefit of CDS and flow coding simultaneously. Through formalized analysis of the routing parameters, CFCR can choose optimized routing with reliable transmission and small cost. Our evaluation shows CFCR has a lower packet loss ratio and higher throughput than existing methods, such as Adaptive Control of Packet Overhead in XOR Network Coding (ACPO), or Distributed Coding-Aware Routing (DCAR).

Routing is one of the most challenging, open problems in disruption-tolerant networks (DTNs) because of the short-lived wireless connectivity environment. To deal with this issue, researchers have investigated routing based on the prediction of future contacts, taking advantage of nodes' mobility history. However, most of the previous work focused on the prediction of whether two nodes would have a contact, without considering the time of the contact. This paper proposes predict and relay (PER), an efficient routing algorithm for DTNs, where nodes determine the probability distribution of future contact times and choose a proper next-hop in order to improve the end-to-end delivery probability. The algorithm is based on two observations: one is that nodes usually move around a set of well-visited landmark points instead of moving randomly; the other is that node mobility behavior is semi-deterministic and could be predicted once there is sufficient mobility history information. Specifically, our approach employs a time-homogeneous semi-Markov process model that describes node mobility as transitions between landmarks. Then, we extend it to handle the scenario where we consider the transition time between two landmarks. A simulation study shows that this approach improves the delivery ratio and also reduces the delivery latency compared to traditional DTN routing schemes.

Routing is one of the most challenging open problems in disruption-tolerant networks (DTNs) because of the short-lived wireless connectivity environment. To deal with this issue, researchers have investigated routing based on the prediction of future contacts, taking advantage of nodes' mobility history. However, most of the previous work focused on the prediction of whether two nodes would have a contact, without considering the time of the contact. This paper proposes predict and relay (PER), an efficient routing algorithm for DTNs, where nodes determine the probability distribution of future contact times and choose a proper next hop in order to improve the end-to-end delivery probability. The algorithm is based on two observations: one is that nodes usually move around a set of well-visited landmark points instead of moving randomly; the other is that node mobility behavior is semi-deterministic and could be predicted once there is sufficient mobility history information. Specifically, our approach employs a time-homogeneous semi-markov process model that describes node mobility as transitions between landmarks. Landmark transition and sojourn time probability distributions are determined from nodes' mobility history. A simulation study shows that this approach improves the delivery ratio and also reduces the delivery latency compared to traditional DTN routing schemes.

The publish/subscribe (pub/sub for short) paradigm is used to deliver events from a source to interested clients in an asynchronous way. Recently, extending a pub/sub system in wireless networks has become a promising topic. However, most existing works focus on pub/sub systems in infrastructured wireless networks. To adapt pub/sub systems to mobile ad hoc networks, we propose DRIP, a dynamic Voronoi region-based pub/sub protocol. In our design, the network is dynamically divided into several Voronoi regions after choosing proper nodes as broker nodes. Each broker node is used to collect subscriptions and detected events, as well as efficiently notify subscribers with matched events in its Voronoi region. Other nodes join their nearest broker nodes to submit subscriptions, publish events, and wait for notifications of their requested events. Broker nodes cooperate with each other for sharing subscriptions and useful events. Our proposal includes two major components: a Voronoi regions construction protocol, and a delivery mechanism that implements the pub/sub paradigm. The effectiveness of DRIP is demonstrated through comprehensive simulation studies.