In coded caching system we prefer to design a coded caching scheme with low subpacketization and small transmission rate (i.e., the low implementation complexity and the efficient transmission during the peak traffic times). Placement delivery arrays (PDA) can be used to design code caching schemes. In this article we propose a framework of constructing PDAs via Hamming distance. As an application, two classes of coded caching schemes with linear subpacketizations and small transmission rates are obtained.

Coded caching systems have been widely studied to reduce the data transmission during the peak traffic time. In practice, two important parameters of a coded caching system should be considered, i.e., the transmission rate which is the maximum amount of the data transmission during the peak traffic time, and the subpacketization level, the number of divided packets of each file when we implement a coded caching scheme. Although there exists a tradeoff between transmission rate and subpacketization, we prefer to design a scheme with transmission rate and subpacketization as small as possible since they reflect the transmission efficiency and complexity of the caching scheme, respectively. In this paper, we first characterize a coded caching scheme from the viewpoint of linear algebra and show that designing a linear coded caching scheme is equivalent to constructing three classes of matrices satisfying some rank conditions. Then based on the invariant subspaces in linear algebra and combinatorial design theory, a new class of coded caching schemes over F2is obtained by constructing these three classes of matrices. It turns out that the transmission rate of our new scheme is the same as the scheme construct by Yan et al. (IEEE Trans. Inf. Theory 63, 5821-5833, 2017), but the subpacketization is significantly reduced. Finally by means of these matrices, we show that the minimum storage regenerating codes can also be used to construct coded caching schemes.

In an (H, r) combination network, a single content library is serving for (rH)users through H relays, where each user has local cache memories and simultaneously accesses a subset of r relays on orthogonal non-interfering and error-free channels. The combinatorial placement delivery array (CPDA in short) can be used to realize a coded caching scheme for combination networks. In this paper, a new algorithm used to realize a scheme for combination networks based on a CPDA is proposed. Based on the fixed CPDA, the scheme realized by our algorithm has smaller subpacketization. Then we focus on directly constructing CPDAs for any positive integers H and r with r <; H and obtain two new classes of CPDAs. Compared with the previously known CPDAs, the schemes realized by our CPDAs have significant advantages on the subpacketization levels with some costing of transmission rates.

Radio Frequency Identification (RFID) plays a key role in the Internet of things (IoT). The type of scenario that needs to use many readers to cover a large area is a dense RFID environment scenario. In supply-chain management, companies such as Wal-Mart use dense RFID reader systems to track products [1]. Collisions usually happen in dense RFID reader systems, which reduce the number of tags that can be read by the system. Many algorithms were designed to eliminate the collisions in a dense RFID environment. A Maximum-Weight-Independent-Set-Based Algorithm (MWISBA) [2] is used to solve the dense RFID readers' arrangement uses a graph-based algorithm to get the MWIS. However, MWISBA does not consider interference range, it can only avoid reader-to-tag collisions. Based on MWISBA, an improved algorithm called MWISBAII [3] can avoid both reader-to-tag collisions and reader-to-reader collisions. However, both MWISBA and MWISBAII are centralized algorithms. In this paper, we propose a distributed realization of MWISBAII. In our distributed algorithm, each reader can communicate with other neighbor readers to share and collect information; making the local decision afterwards. The experimental results show that our distributed algorithm can get almost the same performance as the MWISBAII.

In this paper we consider indoor location based on WiFi signals under the condition that the location provider does not know the physical location of the access points. This scenario is different from most previous researches on indoor location. We proposed several algorithms for this purpose including set calibration data, calculate position and track moving rout. Results from some experiments show that our scheme is useful for many kind buildings such as Malls and office buildings.

In this paper, we proposed a vector signature scheme for face recognition. Using the signature, both the database size and communication bandwidth can be reduced. And the privacy of the face image is also improved. Some experimental implementation shows the potential of the new proposal.

We proposed an algorithm for gateway and router to prevent DDoS attacks. The algorithm combines two simple congestion control methods. Simulation results show that our algorithm efficiently increases the throughput of normal flows under DDoS attacks comparing to common Drop Tail algorithm.

We investigated the particular case of heterogeneous devices used in location based applications. The results suggest applying relative signal strength readings to overcome variations in the wireless characteristics of different devices. An experiment was used to determine an optimum data collection interval. Finally, a full end-to-end reference implementation is constructed. The results show that heterogeneous commodity devices can achieve good localization without a calibration period or expert site surveying.

To share data with other parties in computer collaboration is an important issue of data security. k-anonymity and ℓ-diversity are used to protect privacy and secure data sharing. It was proved that optimal k-anonymity are NP hard for k ≥ 3 and that there is a polynomial algorithm for optimal 2-anonymity. This paper proves that an optimal 2-diversity is NP hard. Since ℓ-diversity must be ℓ-anonymity, it follows that the ℓ-diversity is NP hard for ℓ ≥ 2. The result shows that finding polynomial algorithm for efficient (but not optimal) ℓ-diversity is important.

Electronic business or on-line cooperation transactions happen regularly over the internet. Such a transaction usually involves a service provider who provides a certain service (i.e., perform an on-line purchase) and a service requester who requests the service. In order to decide whether a service requester can access a service, a distributed access control system can be used. Traditional identity-based access control systems usually require pre-register, which is too rigid to adapt to the rapid developing on-line cooperation. Trust-based access control provides open authentication and access control. The flexibility that it introduces could boost the on-line cooperation significantly. However, it is vulnerable to attacks that lead to leakage of sensitive information. Furthermore, certain credentials (such as, credit card number) are too sensitive to release for some people even through proper release policies. This paper introduces the Zero-knowledge protocol for credential verification, and presents a trust-based access control framework that incorporates this protocol. This system keeps the highly sensitive credentials secret; while at the same time proceed with the trust negotiation.

Optical orthogonal codes (OOCs) have been designed for OCDMA. A one-dimensional (1-D) optical orthogonal code (1-D OOC) is a set of one-dimensional binary sequences having good auto and cross-correlations. One limitation of 1-D OOC is that the length of the sequence increases rapidly when the number of users or the weight of the code is increased, which means large bandwidth expansion is required if a big number of codewords is needed. To lessen this problem, two-dimensional (2-D) coding (also called multiwavelength OOCs) was invested. A two dimensional (2-D) optical orthogonal code (2-D OOC) is a set of utimesv matrices with (0, 1) elements having good auto and cross-correlations. Recently, many researchers are working on constructions and designs of 2-D OOCs. In this paper, we shall reveal the combinatorial properties of 2-D OOCs and give an equivalent combinatorial description of a 2-D OOC. Based on this, we are able to use combinatorial methods to obtain many optimal 2-D OOCs.

Privacy preservation during cooperation has become an interesting issue in the last few years. This problem attracted much research work. k-anonymization is an efficient approach to protect data privacy. However, k-anonymization problem was proven NP-hard though the idea of k-anonymizafion is not complex. In this paper, we propose two simple but very efficient algorithms, which work for numeric and categorical data respectively, can minimize information loss as low as possible. We show that these algorithms can produce better performance comparing to other known algorithms.

Currently, the use of transfer information is becoming critical for organizations. Collaborative activities such as coordination, decision making and negotiation depend on it. Organizational memory systems (OMS) have been proposed to accumulate, organize, preserve and share diverse information coming from various sources. However, the need to provide privacy capability to all the users of an OMS requires a good strategy for acquiring and structuring the information. This paper presents a new privacy mechanism strategy for the information stored in the OMS.

In this paper, we consider aperiodic correlation of complex maximum-Welch-bound-equality (MWBE) sequence constructed from difference sets. An MWBE sequence set is optimal in synchronous cross-correlation. However, for different ordered lists of the elements in a difference set, the corresponding MWBE sequences have different aperiodic auto- and cross- correlations. Several search algorithms are developed to find a good ordered list of the elements in a difference set so that the corresponding MWBE sequence set has low aperiodic correlations which can be less than radicN In N. In addition, the aperiodic correlation is further reduced by a deletion-based method.

We propose an exception resolution service for a role based access control (RBAC) system as a supplementary service, that will increase the flexibility of RBAC systems. Our model will keep the security policies based on a RBAC system while some not role based administrations are possible. In other words, the not role based access permission is not independent from the RBAC system. The related definitions and functions are given. An implementation example shows that the service is useful and efficient in practice.

Agent-based e-business opens up a computational direction, in which software agents behave on behalf of their owners. However, enabling agents to make decisions and exploiting information to other unknown agents have introduced some security challenges among them is trust relationship while agents are dealing with unknown environments and their residences. Despite existing of some sophisticated proposed approaches addressing the above problem, most of them are suffering from complexity and therefore drawback from development. We propose an efficient trust model for distributed systems mainly focusing on multi-agent systems. We provide a feasible mechanism using some well-known cryptographic techniques such that not only it addresses the above issue but also guarantees the security and resistibility of the model against some attacks

A successful result of choosing, invoking, integrating and composing services in a collaborative environment depends directly on locating reliable services with respect to their performances, histories, feedbacks from their customers, and generally their reputations. Nevertheless, lacking a secure mechanism to create countable reputation information may lead service providers to exaggerate their performances. We propose to apply threshold schemes under the context of service reputation towards providing an unconditionally secure "reputation" credits and systems for services and their providers. We argue that applying such a secure mechanism for reputation of services is not forgeable. As a result, any service requester was able to rely on valuable reputation information and choose the most reliable services with confidence.

In order to protect copyrighted material, codes may be embedded in the content or codes may be associated with the keys used to recover the content. Codes can offer protection by providing some form of traceability (TA) for pirated data. Several researchers have studied different notions of TA and related concepts in previous years. "Strong" versions of TA allow at least one member of a coalition that constructs a "pirate decoder" to be traced. Weaker versions of this concept ensure that no coalition can "frame" a disjoint user or group of users. All these concepts can be formulated as codes having certain combinatorial properties. We study the relationships between the various notions, and we discuss equivalent formulations using structures such as perfect hash families. We use methods from combinatorics and coding theory to provide bounds (necessary conditions) and constructions (sufficient conditions) for the objects of interest.

In this paper, we investigate combinatorial properties and constructions of two recent topics of cryptographic interest, namely frameproof codes for digital fingerprinting and traceability schemes for broadcast encryption. We first give combinatorial descriptions of these two objects in terms of set systems and also discuss the Hamming distance of frameproof codes when viewed as error-correcting codes. From these descriptions, it is seen that existence of a c-traceability scheme implies the existence of a c-frameproof code. We then give several constructions of frameproof codes and traceability schemes by using combinatorial structures such as t-designs, packing designs, error-correcting codes, and perfect hash families. We also investigate embeddings of frameproof codes and traceability schemes, which allow a given scheme to be expanded at a later date to accommodate more users. Finally, we look briefly at bounds which establish necessary conditions for existence of these structures.