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Welcome to this special issue of Wireless Personal Communications. This issue contains a collection of the best papers out of various authors who have been submitted to this issue. The main goal for this issue is to be a timely vehicle for publishing selected research papers from practitioners and academia in convergence industries on this emerging topic. This issue covers some of the hottest topics in Convergence Interaction for Communication, including: convergence; interactive applications; cloud service; P2P architectures and wireless protocols; data and index structures; motion recognition; future communication system; hybrid networking system; spectrum resource allocation; personal networking and architectures; multiple access techniques; multicasting and computer communications. The paper by Mun et al. [1] proposes the injecting of a subject policy into access control to strengthen the protection of personal information. This study provides two confidential access control models that apply individually established policies to the role-based access control model (RBAC) and the mandatory access control model (MAC) technologies. In the SpRBAC model, a user’s right to access would follow organizational policy, and accessing personal information would be restricted by the subject policy. In the SpMAC model, users would have to satisfy the subject policy established by the provider of the information, in addition to the requirements of the normal MAC policy. The paper by Lee et al. [2] presents variability change management using orthogonal variability model-based traceability. The proposed method is an approach to tracing variability based on explicit

In this paper we propose a machine learning-based fast intra-prediction mode decision algorithm, using random forest that is an ensemble model of randomized decision trees. The random forest is used to estimate an intra-prediction mode from a prediction unit and to reduce encoding time significantly by avoiding the intensive Rate-Distortion optimization of a number of intra-prediction modes. To this aim, we develop a randomized tree model including parameterized split functions at nodes to learn directional block-based features. The feature uses only four pixels reflecting a directional property of a block, and, thus the evaluation is fast and efficient. To integrate the proposed technique into the conventional video coding standard frameworks, the intra-prediction mode derived from the proposed technique, called an inferred mode (IM), is used to shrink the pool of the candidate modes before carrying out the Rate-Distortion (R-D) optimization. The proposed technique is implemented into the High Efficiency Video Coding Test Model (HM) reference software of the state-of-the-art video coding standard and Joint Exploration Model (JEM) reference software, by integrating the random forest trained off-line into the codecs. Experimental results demonstrate that the proposed technique achieves significant encoding time reduction with only slight coding loss as compared the reference software models.

To address the ever increasing demand for wireless bandwidth, cognitive radio networks (CRNs) have been proposed to improve the efficiency of channel utilization. CRN permits unlicensed users to utilize the idle spectrum as long as it does not introduce interference to the primary users due to the Federal Communications Commission’s recent regulatory policies. In this paper, we first identify some required distinctive security and privacy features for CRNs focused on ECMA-392, which is the first industrial standard for personal or portable devices in the television white spaces. After that, we propose a delegation based user authentication framework as a basic security and privacy module with full consideration of the required features over CRNs. The proposed framework provides privacy preserving yet accountable security within the CRN entities. Security and privacy analyses show that the proposed framework supports unlinkability, context privacy, anonymity, no registration and conditional traceability, which are the required security and privacy aspects in CRNs.

People today have become more interested in disease prevention and health promotion, rather thandisease treatment, and have shown a tendency to get various types of information from diverse mediaand try to apply it to themselves. Numerous and varied health information web sites have been devel-oped and are now operating. However, they do not seem to actually be effective for users’ healthcareneeds and health promotion, not only because of the limitations of web-based information, but also dueto a lack of customized healthcare services. In the current ubiquitous environment, health informationsupportserviceshavegenerallybeendevelopedin aformat ofinputting bio-information into acomputerfor network-based transmission. For that reason, they are, in fact, quite inconvenient and inefficient. Inthis regard, what is urgently required is to develop a method to supply smart healthcare using conver-gence technologies [1–7]. Therefore, noveltechniques, architectures, algorithms, experiencesregardingmultimedia applications, and industry services should be considered. Some of these research areas arelisted below.– Health computing for convergence– Bioelectronics, biomechanics,telemedicine– Medical imaging, bio-imaging– Surgical technology,medical physics– Innovativeapplications for convergencehealthcare– Artificial organs, biomaterials– Medical information technology– Medical and hospital informatics

Recently, because the interest and needs in privacy protection are growing, smartcard-based remote user authentication schemes have been actively studied to provide the user anonymity. In 2008, Kim et al. first proposed an authentication scheme in order to ensure the user anonymity against both external attackers and the remote server and track malicious users with the help of a trusted trace sever. However, in 2010, Lee et al. showed that Kim et al.`s scheme cannot provide the user anonymity against remote server, which is because the server can trace users without any help of the trace server, and then proposed a improved scheme. On the other hand, in 2010, Horng et al. proposed an authentication scheme with non-tamper resistant smart cards, in which the non-tamper resistant smart card means that an attacker may find out secret information stored in the smart card through special data analysis techniques such as monitoring power consumption, to be secure against a variety of attacks and to provide the user anonymity against external attackers. In this paper, we will propose a remote user authentication scheme with non-tamper resistant smart cards not only to ensure the user anonymity against both external attackers and the remote server but also to track malicious users with only the help of a trusted trace sever.

In a paper recently published in the International Journal of Parallel, Emergent and Distributed Systems, Biswas et al. proposed a VANET message authentication scheme which uses an identity-based proxy signature mechanism as an underlying primitive. The authors claimed that their scheme supports various security features including the security of proxy-key, the security against message forgery and the security against replay attack, with non-repudiation and resistance to proxy-key compromise. Here, we show how an active attacker, who has no knowledge of an original message sender`s private key, can compute the proxy-signature key of the corresponding message sender, meaning that the scheme is completely insecure. We also suggest an enhanced version of the protocol capable of solving such serious security holes.

Intelligent bio-sensor information processing was developed using lifelog based context aware technology to provide a flexible and dynamic range of diagnostic capabilities to satisfy healthcare requirements in ubiquitous and mobile computing environments. To accomplish this, various noise signals were grouped into six categories by context estimation and effectively reconfigured noise reduction filters by neural network and genetic algorithm. The neural network-based control module effectively selected an optimal filter block by noise context-based clustering in running mode, and filtering performance was improved by genetic algorithm in evolution mode. Due to its adaptive criteria, genetic algorithm was used to explore the action configuration for each identified bio-context to implement our concept. Our proposed Bio-interactive healthcare service system adopts the concepts of biological context-awareness with evolutionary computations in working environments modeled and identified as bio-sensors based environmental contexts. We used an unsupervised learning algorithm for lifelog based context modeling and a supervised learning algorithm for context identification.

Hazard Analysis Critical Control Points (HACCP), internationally recognized as an effective way of controlling foodborne hazards, has been progressively applied for the benefit of the food industry. However, HACCP is a difficult principle to apply. Failure to perform hazard analysis could render the entire HACCP plan ineffective. This paper describes a new analytical method using simple beta and triangular probability distributions to improve the hazard analysis stage of the HACCP plan. Developed in Microsoft® Excel (a spreadsheet program), the model calculates the risk level for the probability, i.e., the likelihood of occurrence of a specific hazard by using background information and data. A pork-cutting procedure was included in a case study. At a 50% percentile value in probability distribution, the highest risk was a biological hazard (e.g., foodborne pathogens growth) in the packaging steps, at a probability of 5.5 × 10−1. The lowest risk was a physical hazard in the packaging steps (e.g., foreign materials introduced by packaging damage), at a probability of 1.4 × 10−3. Despite certain shortcomings, this model, with further improvements, could be expected to increase the effectiveness of HACCP in controlling food safety.

Recently, many works have been focusing on solving the problem of privacy protection at link-layer level by randomizing all bits of the frames at link layer so that it makes difficult for unintended recipients to associate sequences of packets to their source transmitters. Most existing schemes however assume either the pre-setup for shared secrets between communication entities or the use of public-key infrastructure. These requirements limit the use of the schemes. In this paper, we describe new techniques for protecting the privacy and security of communication entities at wireless link-layer level. Our techniques have a number of crucial advantages. They mitigate the requirement of a key setup or a public-key infrastructure. They provide not only the link-layer privacy, but also the required security properties, including key compromise impersonation resilience, impersonation resistance and forward secrecy. They are simple and relatively fast.

It is important for the strategy of service to provide the health information in the environment that the healthcare has been changed focusing on the preventive medicine. Recently, the various applications of u-healthcare have been presented by researchers. In this paper, we proposed the health information monitoring system using the context sensors based band. By wearing the proposed hand, the health status is gathered and vital signals are transmitted to the connected UMPC. It can be easily monitored according to the user locations in real time. To provide the health index according to the temperature, the air conditioning, the illumination, the humidity, and the ultraviolet rays, we use the various XML links extracted from RSS of the Korea Meteorological Administration. The health information is analyzed in terms of factors, such as, the asthma index, the stroke index, the skin disease index, the pulmonary disease index, the pollen concentration index, and the city high temperature index. Ultimately, this paper suggests empirical application to verify the adequacy and the validity with the proposed system. Accordingly, the satisfaction and the quality of services will be improved the healthcare.

The customer relation marketing in which companies can utilize to control and to get the filtered information efficiently has appeared in ubiquitous commerce. It is applying data mining technique to build the management that can even predict and recommend products to customers. In this paper, we proposed the case of customer relation management application using the associative mining. The proposed method uses the associative mining composes frequent customers with occurrence of candidate customer-set creates the association rules. We analyzed the efficient the feature of purchase customers using the hypergraph partition according to the lift of creative association rules. Therefore, we discovered strategies of the cross-selling and the up-selling. To estimate the performance, the suggested method is compared with the existing methods in the questionnaire dataset. The results have shown that the proposed method significantly outperforms the accuracy than the previous methods.

With the advance of information technologies and the spread of Internet use, the volume of usable information is increasing explosively. A content recommendation system provides the services of filtering out information that users do not want and recommending useful information. Existing recommendation systems analyze the records and patterns of Web connection and information demanded by users through data mining techniques and provide contents from the service provider`s viewpoint. Because it is hard to express information on the users` side such as users` preference and lifestyle, only limited services can be provided. The semantic Web technology can define meaningful relations among data so that information can be collected, processed and applied according to purpose for all objects including images and documents. The present study proposes a content recommendation search system that can update and reflect personalized profiles dynamically in semantic Web environment. A personalized profile is composed of Collector that contains the characteristics of the profile, Aggregator that collects profile data from various collectors, and Resolver that interprets profile collectors specific to profile characteristic. The personalized module helps the content recommendation server make regular synchronization with the personalized profile. Choosing music as a recommended content, we conduct an experience on whether the personalized profile delivers the content to the content recommendation server according to a service scenario and the server provides a recommendation list reflecting the user`s preference and lifestyle.

An untraceable RFID authentication scheme allows a legitimate reader to authenticate a tag, and at the same time it assures the privacy of the tag against unauthorized tracing. In this paper, we revisit three elliptic-curve based untraceable RFID authentication protocols recently published and show they are not secure against active attacks and do not support the untraceability for tags. We also provide a new construction to solve such problems using the elliptic-curved based Schnorr signature technique. Our construction satisfies all requirements for RFID security and privacy including replay protection, impersonation resistance, untraceability, and forward privacy. It requires only two point scalar multiplications and two hash operations with two messages exchanges. Compared to previous works, our construction has better security and efficiency.

A user identification scheme was proposed by Tseng et al. in 1998, as one of applications that are based on the ideas of ID-based cryptosystems. Recently, Hwang et al. presented an improvement of the Tseng et al.' scheme for wireless mobile environment. In wireless environment, the time for waiting and responding of a mobile device must be reduced due to the lack of the capacity of the battery. The authors tried to achieve this goal by optimizing the pass of the scheme. However, here we show their scheme has some limitation for practical usage in the sense that it is not secure against a key compromise impersonation attack.

In 2004, Peinado pointed out that LHL-key authentication scheme is not secure as the intruder can obtain the private key of the users. For enhancing the security, Peinado proposed an improved LHL-key authentication scheme. However, in this paper, we will show that Peinado's improved LHL-key authentication scheme is still vulnerable to public key substitution attack, i.e., an intruder can substitute a fake public key for the genuine one. And then, we propose a further improved LHL-key authentication scheme resistant to public key substitution attack.

Recently, an efficient and non-interactive deniable authentication protocol based on the Diffie-Hellman key distribution protocol is presented by Fan et al. to enable a receiver to identify the source of a given message, but not prove the identity of the sender to a third party. In this paper, we point out that it suffers from an authentication flaw similar to that developed by Lowe to Intruder masquerades as other principals and inquisitor INQ can identify the source of the message unlike their claims. Accordingly, we propose an improved protocol to overcome the weaknesses.

Recently, Tseng and Jan presented anonymous conference key distribution systems that make use of the interpolating properties of polynomials. However, their protocol has some limitations in that users are not able to check the correctness of the distributed conference key but also verify if they take part in any particular protocol run. This leads to the possibility of an active attack. In this article, we show that Tseng and Jan's protocol does not work properly because of its incompleteness. We also describe a simple and promising remedy to such a problem.

In 2004, Chien and Jan pointed out that Yeh et al.'s authenticated multiple-key key agreement protocol was vulnerable to the impersonation attack. For enhancing the security and key utilization, Chien and Jan proposed an improved protocol. However, Yang and Wang showed that Chien-Jan's protocol is vulnerable to the impersonation attack. This paper proposes an improved protocol to overcome the weakness while maintaining the advantages of Chien-Jan's protocol.

Recently, Lin et al. proposed an improvement on the OSPA protocol to make the protocol withstand the stolen-verifier attack, using smart card. However, Ku et al. demonstrated that Lin et al.’s protocol is vulnerable to the replay attack and the denial of service attack. In this paper, we will propose an enhancement of the protocol to isolate such problems. As a result, the proposed scheme can simply update user passwords and also provides mutual authentication between the user and a remote server. Besides all the above merits, the proposed has more efficient performance by reducing the number of hash operations.

Recently, Lee and Lee showed that the Hsu et al. improvement of modified authenticated key agreement scheme is vulnerable to the modification attack and proposed an improvement to withstand this attack. However, this paper will first show that this improvement is vulnerable to the guessing attack, and then propose an improvement to eliminate this security flaw.

Recently, Hwang-Lee-Tang proposed a simple remote user authentication scheme using smart card, whereby it does not require any password or verification tables in the remote system and any legal users could choose and change their passwords freely. However, their schemes previously generated user's secret hash values are insecure if the secret key of the server is leaked or is stolen, also when the smart card is stolen, unauthorized users can easily change new password of the smart card. Furthermore, their scheme cannot resist the denial of service attack using stolen smart card and does not provide mutual authentication. Accordingly, the current paper demonstrates the vulnerability of Hwang-Lee-Tang's scheme and presents an enhancement to resolve such problems. As a result, the proposed scheme previously generated secret hash values are secure even if the secret key of the system is leaked or is stolen and enables users to update their passwords freely and securely, while also providing mutual authentication and fast detect it when user inputs wrong password. In addition, the computational costs of this scheme are less than those of any previously proposed schemes.

Recently, Lee et al. proposed an improvement on Peyravian and Zunic scheme to make the protocol withstand the guessing attack. However, their scheme suffers from a denial of service attack. In this paper, we show that an attacker can easily prevent the normal use of communication facilities by performing the attack. We also propose an enhancement of the scheme to isolate such a problem.

In 2003, Shen et al. proposed an improvement on Yang-Shieh's timestamp-based password authentication scheme using smart cards. Then they claimed that their scheme cannot withstand a forged login attack, but also eliminatea problem of Yang-Shieh's. However, their scheme is still susceptible to forged login attack. In this letter, we show how the forged login attack can be worked out on Shen et al.'s scheme.

With the increasing number of chronic disease patients, the importance of everyday health care has grown more significant. The study researchers expected it would help for patients' health improvement and healthcare service expansion if users check their vital signs in their daily lives and send the results to a medical center's servers through a specific device automatically. This thesis, in line with this idea, seeks to develop a portable healthcare gateway. The gateway is designed in a USB type and can transmit standardized data, operating regardless of a user's location and Personal Healthcare Devices (PHDs).

Recently, Shen et al. proposed an improvement to Hwang-Li's scheme to prevent from forgery attack. However, Leung et al. pointed out that this improved scheme is still susceptible to forgery attack proposed by Chan and Cheng. Accordingly, the current paper presents an enhancement based on generalized ElGamal signature scheme to resolve such problems. As a result, the proposed scheme enables users to update their passwords freely without the help of a remote system, while also providing mutual authentication. In addition, the computational costs of this scheme are less than those of previously proposed schemes.

Recently, Ku-Chen proposed an improvement to Chien et al.'s scheme to prevent from some weaknesses. However, the improved scheme is not only still susceptible to parallel session attack, but also insecure for changing the user's password in password change phase. Accordingly, the current paper presents an enhancement to resolve such problems. As a result, the proposed scheme enables users to change their passwords freely and securely without the help of a remote server, while also providing secure mutual authentication.

The range of ubiquitous computing technology available for use in healthcare continues to evolve, allowing for an increasing variety of wireless sensors, devices, and actuators to be deployed in changing environments. This paper presents a robust distributed architecture for adaptive and intelligent bio-interaction systems, called Evolutionary Bio-inspired Knowledge Accumulation. This system is designed to its capability to increase knowledge enhancement even in dynamic and uneven environments. Our proposed system adopts the concepts of biological context-awareness with evolutionary computations where the working environments are modeled and identified as bio-environmental contexts. We have used an unsupervised learning algorithm for bio-context modeling, and a supervised learning algorithm for context identification. A genetic algorithm, for its adaptive criteria, is used to explore action configuration for each identified bio context to implement our concept. This framework has been used to reduce noise in ECG signals that have been gathered in routine remote healthcare monitoring. Experimental results showed that the proposed algorithm effectively removes baseline wander noise and muscle noise, and feature extraction results showed a significant improvement of T duration extraction values.

Recently, the problem of protecting privacy at link-layer is of great importance in wireless environments, mainly due to the fact that the wireless link layer is not protected by current technologies used in wireless networks. This leads to many potential threats to security and user privacy. Very recently, Lu et al. proposed an authentication scheme for wireless link-layer privacy which is based on the idea of identity-based encryption from bilinear pairings. The scheme however does not support the security against the type of known-key attack, called key-compromise impersonation. This limits the use of the scheme in that such a security hole can potentially be extended to many additional attacks, causing more serious consequences in practice. In this paper, we demonstrate that how the attack can be launched and also provide an enhanced construction in order to solve the problem. Our scheme has almost the same performance as that of Lu et al. in terms of both computation and communication cost, while it provides much better security results.

The existing music search and recommendation systems obtain results through query or answer and recommend music using data mining techniques. However, it is not possible to provide active services that satisfy customers in smart home environments because these systems consider only static information in Web environments. In order to solve these problems, this paper attempts to define context information to use select music and design a ubiquitous music recommendation system that is suited to a user's interests and preferences using hidden Markov model for music items. The recommendation system used in this study uses an OSGi framework to recognize context information and increase satisfaction of service.

A detailed model of a transaction processing system with dynamic locking is developed and analyzed. Transaction classes are distinguished on the basis of the number of data items accessed and the access mode (read-only/update). The performance of the system is affected by transaction blocking and restarts, due to lock conflicts that do not or do cause deadlocks, respectively. The probability of these events is determined by the characteristics of transactions and the database access pattern. Hardware resource contention due to concurrent transaction processing is taken into account by specifying the throughput characteristic of the computer system for processing transactions when there is no data contention. A solution method based on decomposition is developed to analyze the system, and also used as the basis of an iterative scheme with reduced computational cost. The analysis to estimate the probability of lock conflicts and deadlocks is based on the mean number of locks held by transactions. These probabilities are used to derive the state transition probabilities for the Markov chain specifying the transitions among the system states. The decomposition solution method and the associated iterative scheme are shown to be more accurate than previously defined methods for dynamic locking through validation against simulation results. Several important conclusions regarding the behavior of dynamic locking systems are derived from parametric studies.

A keyword-searchable encryption scheme allows a user with a "trapdoor" for a keyword to efficiently retrieve some of encrypted data containing the specific keyword over a remote server. The scheme for keyword-searchable encryption is considered as one of crucial building blocks that solves the security problems of privacy and data confidentiality in many settings, such as outsourced database systems and mail (or file) servers. However, most existing schemes support only a single keyword for searching, but do not allow for boolean combinations of keywords. It makes the use of schemes impractical in real applications. To address this problem, we propose an efficient construction for conjunctive keyword-searchable encryption, in which the size of trapdoors is almost same as that for searching a single keyword. Our construction is proven secure against adaptive chosen-keyword attacks in the random oracle model under the external co-Diffie-Hellman assumption. Compared to previous works, our construction has much better performance in terms of both computational and communication cost.

Recently, Lin-Hwang proposed a password authentication scheme with secure password updating. The current paper demonstrates the vulnerability of Lin-Hwang's scheme to server data eavesdropping and presents improvements to resolve this problem. In contrast to Lin-Hwang's scheme, the proposed scheme can simply update user passwords without a complicated process and provide explicit key authentication in the case of a session key agreement.

In public key cryptosystem, it is very important to protect and authenticate a user's public key. In the past, many schemes have been proposed. However, most of the schemes require one or more authorities to authenticate the public key. In the authority-based scheme, since an authority can know user's private keys or generate false certificates, we can impersonate any user at any time. Therefore, it is required such a scheme as an authority cannot know the secret information of users and a security of system does not wholly depend on an authority. In recent years, Zhan et al. proposed a new key authentication scheme, called ZLYH-scheme, which is requires no authority to authenticate a user's public key. However, it still has a weakness that can guess password. We show that ZLYH-scheme has some weakness. To overcome this disadvantage, we propose an improved key authentication scheme. In our scheme, it does not require the secret password table and an attacker cannot guess the password.

Recently, Lee-Lee pointed out that Hsu et al.’s key agreement scheme suffers from a modification attack and described an enhancement on it. Both of Lee-Lee’s enhancement and Hsu et al. scheme can be considered as variants of Diffie-Hellman scheme with user authentication that are based on a shared-password for providing authentication. This paper shows both schemes cannot withstand to a dictionary attack. Such an attack illustrates that extreme care must be taken when passwords are combined to provide user authentication in cryptographic protocols. This paper also presents a new authenticated key agreement protocol that is not secure to the dictionary attack but also has many desirable security properties, including forward secrecy and known-key secrecy. It is also able to withstand to both passive and active attacks. The security of the proposed scheme is based on the well-known cryptographic assumptions.

Recently, Shen et al. proposed an improvement on Yang-Shieh’s timestamp-based password authentication scheme using smart cards. Then they claimed that their scheme cannot withstand a forged login attack, but also eliminate a problem of Yang-Shieh’s. However, their scheme is still susceptible to forged login attack. In this paper, we show how the forged login attack can be worked out on Shen et al.’s scheme and present an enhancement to resolve such a problem.

Recently, multiparty key agreement protocols with cheater identification based on Shamir secret sharing was presented by Pieprzyk and Li and Y. M. Tseng, respectively. However, in their multiparty key agreement protocols there are mistakes in computing a common secret key. Also Tseng’s cheater identification scheme cannot identify cheaters perfectly. In this paper, we present a concrete multiparty key agreement protocol with more efficient and perfect cheater identification than Tseng’s protocol in computations and communications. Performance comparison and security analysis are given in this paper.

In this paper, we describe a new ID-based authenticated key agreement protocol that makes use of bilinear pairings. We then discuss the security properties of our scheme, including known-key security, perfect forward secrecy and no key control. It is also able to withstand both passive and active attacks. An important advantage of our scheme is that it preserves the perfect forward secrecy even though the long-term secret key of a trusted key generation center is compromised. We also show that it is more efficient than Chen and Kudla's protocol with same security properties as ours.

Recently, Wu and Chieu proposed an improvement to Sun’s scheme, whereby users could choose and change their passwords freely through a secure channel when using a remote system. However, this improved scheme is still susceptible to impersonation attacks and does not provide mutual authentication. Accordingly, the current paper demonstrates the vulnerability of Wu and Chieu’s scheme to impersonation attacks and presents an enhancement to resolve such problems. As a result, the proposed scheme enables users to update their passwords freely without the help of a remote system, while also providing mutual authentication.

In 1999, Seo and Sweeney proposed a simple authenticated key agreement protocol(SAKA) that was designed to act as a Diffie-Hellman scheme with user authentication. However, the protocol was subsequently found to have security flaws and enhanced in the literature. Recently, Ku and Wang showed a variant of SAKA. This paper shows that the Ku and Wang’s scheme is still vulnerable to an off-line password guessing attack. The attack illustrates that extreme care must be taken when passwords are combined to provide user authentication in the key agreement protocols. This paper also presents a new key agreement protocol that resists the guessing attacks mounted by either passive or active network attackers, allowing low-entropy passwords to be used safely. The protocol has more efficient performance by reducing the number of protocol steps.

In this paper we analyze Optimistic Concurrency Control (OCC) schemes based on certification. We allow two data access schemes referred to as static and dynamic . A static data access scheme implies that all data items are accessed at the beginning of transaction processing, while data items are accessed on demand during the processing of a transaction in a dynamic scheme. After completing its processing, each transaction is validated, i.e., checked as to whether it has encountered a data conflict. Validated transactions commit; otherwise, they are restarted. A variant of the regular (silent) commit scheme where a committing transaction notifies conflicted transactions to restart immediately (broadcast commit scheme) is also considered. System efficiency or the fraction of useful work as affected by data contention is used as the main performance measure. We develop an iterative solution method to analyze the performance of OCC schemes in the framework of a system with a fixed number of transactions in multiple classes with given occurrence frequencies. The model is analyzed by (iteratively) solving a set of nonlinear equations which relate per class efficiencies to system efficiency. The iterative solution method is validated against simulation and shown to be highly accurate even for high data contention. An advantage of the iterative solution method is that it separates the analysis of data contention from hardware resource contention and provides per class efficiencies. We present graphs/tables, which are used to determine how system performance is affected by: (i) various OCC schemes, (ii) the distribution of transaction processing times, (iii) transaction size and its distribution, and (iv) the throughput characteristics of the system (as determined by hardware contention).

Optimistic Concurrency Control-OCC schemes based on certification are analyzed in this paper. We allow two types of data access schemes referred to as static and dynamic. According to the first (second) scheme a transaction reads all the required data items at the beginning of its processing (on demand during its processing), respectively. After completing its processing, each transaction is checked as to whether it has encountered a data conflict. Validated transactions commit; otherwise, they are restarted. A variant of the regular (silent) commit scheme where a committing transaction notifies conflicted transactions to restart immediately (broadcast commit scheme) is also considered. We use an iterative method to analyze the performance of OCC schemes in the framework of a system with a fixed number of transactions in multiple classes with given probabilities for their occurrence. The iterative method is validated against simulation and shown to be highly accurate even for high data contention. We present graphs/tables, which are used to determine how system performance is affected by: (i) various OCC schemes, (ii) transaction size, i.e., number of data items accessed, (iii) number of transactions, (iv) the distribution of transaction processing time requirements, (v) the throughput characteristic of the system, and (vi) granule placement.

The effect of concurrency control methods on the performance of computer systems is analyzed in the context of a centralized database with a static lock request policy, i.e., database transactions should acquire all locks before their activation. In the lock conflict model the L locks required by each transaction are uniformly distributed over the N locks in the database. The computer system is modelled as a queueing network. Two scheduling policies for transaction activation are considered: FCFS with and without skip. In each case the scheduling overhead for scanning the blocked transactions is taken into account. The number of transactions to be scanned is limited by a window size parameter. The system is analyzed using a hierarchical decomposition method, where the highest level model yields the mean user response time. The results of the approximate solution are validated using a detailed simulation, which shows that the analysis based on no resampling of locks is quite accurate and outperforms the simplified analysis with resampling of locks in accuracy. The effect of varying the values of parameters such as transaction size, granularity of locking, scheduling discipline for transaction activation, scheduling overhead, and window size on system performance is investigated.

We propose a simple key agreement protocol(SKA) that provides key establishment with authentication over an insecure channel using only a human memorable password. The SKA is based on Diffie-Hellman scheme and has many of desirable security attributes: it resists off-line dictionary attacks mounted by either passive or active adversaries over network, allowing low-entropy passwords to be used safely. It also offers perfect forward secrecy, which protects past sessions and passwords against future compromise. Besides, it is secure against an adversary who captured a host's password file. Since user passwords are stored in a verifier form, the adversary cannot use it directly to compromise security. The proposed scheme here shows that it is more efficient in computational time and communication overhead over the existing schemes.