Biblio

Found 2356 results

Filters: Keyword is privacy  [Clear All Filters]
2017-03-08
Chriskos, P., Zoidi, O., Tefas, A., Pitas, I..  2015.  De-identifying facial images using projections on hyperspheres. 2015 11th IEEE International Conference and Workshops on Automatic Face and Gesture Recognition (FG). 04:1–6.

A major issue that arises from mass visual media distribution in modern video sharing, social media and cloud services, is the issue of privacy. Malicious users can use these services to track the actions of certain individuals and/or groups thus violating their privacy. As a result the need to hinder automatic facial image identification in images and videos arises. In this paper we propose a method for de-identifying facial images. Contrary to most de-identification methods, this method manipulates facial images so that humans can still recognize the individual or individuals in an image or video frame, but at the same time common automatic identification algorithms fail to do so. This is achieved by projecting the facial images on a hypersphere. From the conducted experiments it can be verified that this method is effective in reducing the classification accuracy under 10%. Furthermore, in the resulting images the subject can be identified by human viewers.

2017-02-23
H. M. Ruan, M. H. Tsai, Y. N. Huang, Y. H. Liao, C. L. Lei.  2015.  "Discovery of De-identification Policies Considering Re-identification Risks and Information Loss". 2015 10th Asia Joint Conference on Information Security. :69-76.

In data analysis, it is always a tough task to strike the balance between the privacy and the applicability of the data. Due to the demand for individual privacy, the data are being more or less obscured before being released or outsourced to avoid possible privacy leakage. This process is so called de-identification. To discuss a de-identification policy, the most important two aspects should be the re-identification risk and the information loss. In this paper, we introduce a novel policy searching method to efficiently find out proper de-identification policies according to acceptable re-identification risk while retaining the information resided in the data. With the UCI Machine Learning Repository as our real world dataset, the re-identification risk can therefore be able to reflect the true risk of the de-identified data under the de-identification policies. Moreover, using the proposed algorithm, one can then efficiently acquire policies with higher information entropy.

2017-03-08
Sun, Z., Meng, L., Ariyaeeinia, A..  2015.  Distinguishable de-identified faces. 2015 11th IEEE International Conference and Workshops on Automatic Face and Gesture Recognition (FG). 04:1–6.

The k-anonymity approach adopted by k-Same face de-identification methods enables these methods to serve their purpose of privacy protection. However, it also forces every k original faces to share the same de-identified face, making it impossible to track individuals in a k-Same de-identified video. To address this issue, this paper presents an approach to the creation of distinguishable de-identified faces. This new approach can serve privacy protection perfectly whilst producing de-identified faces that are as distinguishable as their original faces.

2017-02-23
H. Ulusoy, M. Kantarcioglu, B. Thuraisingham, L. Khan.  2015.  "Honeypot based unauthorized data access detection in MapReduce systems". 2015 IEEE International Conference on Intelligence and Security Informatics (ISI). :126-131.

The data processing capabilities of MapReduce systems pioneered with the on-demand scalability of cloud computing have enabled the Big Data revolution. However, the data controllers/owners worried about the privacy and accountability impact of storing their data in the cloud infrastructures as the existing cloud computing solutions provide very limited control on the underlying systems. The intuitive approach - encrypting data before uploading to the cloud - is not applicable to MapReduce computation as the data analytics tasks are ad-hoc defined in the MapReduce environment using general programming languages (e.g, Java) and homomorphic encryption methods that can scale to big data do not exist. In this paper, we address the challenges of determining and detecting unauthorized access to data stored in MapReduce based cloud environments. To this end, we introduce alarm raising honeypots distributed over the data that are not accessed by the authorized MapReduce jobs, but only by the attackers and/or unauthorized users. Our analysis shows that unauthorized data accesses can be detected with reasonable performance in MapReduce based cloud environments.

M. Vahidalizadehdizaj, L. Tao.  2015.  "A new mobile payment protocol (GMPCP) by using a new key agreement protocol (GC)". 2015 IEEE International Conference on Intelligence and Security Informatics (ISI). :169-172.

According to the advancement of mobile devices and wireless network technology, these portable devices became the potential devices that can be used for different types of payments. Recently, most of the people would rather to do their activities by their cellphones. On the other hand, there are some issues that hamper the widespread acceptance of mobile payment among people. The traditional ways of mobile payment are not secure enough, since they follow the traditional flow of data. This paper is going to suggest a new protocol named Golden Mobile Pay Center Protocol that is based on client centric model. The suggested protocol downgrade the computational operations and communications that are necessary between the engaging parties and achieves a completely privacy protection for the engaging parties. It avoids transaction repudiation among the engaging parties and will decrease replay attack s risk. The goal of the protocol is to help n users to have payments to each others'. Besides, it will utilize a new key agreement protocol named Golden Circle that is working by employing symmetric key operations. GMPCP uses GC for generating a shared session key between n users.

2017-03-07
Adebayo, O. J., ASuleiman, I., Ade, A. Y., Ganiyu, S. O., Alabi, I. O..  2015.  Digital Forensic analysis for enhancing information security. 2015 International Conference on Cyberspace (CYBER-Abuja). :38–44.

Digital Forensics is an area of Forensics Science that uses the application of scientific method toward crime investigation. The thwarting of forensic evidence is known as anti-forensics, the aim of which is ambiguous in the sense that it could be bad or good. The aim of this project is to simulate digital crimes scenario and carry out forensic and anti-forensic analysis to enhance security. This project uses several forensics and anti-forensic tools and techniques to carry out this work. The data analyzed were gotten from result of the simulation. The results reveal that although it might be difficult to investigate digital crime but with the help of sophisticated forensic tools/anti-forensics tools it can be accomplished.

2017-02-23
K. Pawar, M. Patil.  2015.  "Pattern classification under attack on spam filtering". 2015 IEEE International Conference on Research in Computational Intelligence and Communication Networks (ICRCICN). :197-201.

Spam Filtering is an adversary application in which data can be purposely employed by humans to attenuate their operation. Statistical spam filters are manifest to be vulnerable to adversarial attacks. To evaluate security issues related to spam filtering numerous machine learning systems are used. For adversary applications some Pattern classification systems are ordinarily used, since these systems are based on classical theory and design approaches do not take into account adversarial settings. Pattern classification system display vulnerabilities (i.e. a weakness that grants an attacker to reduce assurance on system's information) to several potential attacks, allowing adversaries to attenuate their effectiveness. In this paper, security evaluation of spam email using pattern classifier during an attack is addressed which degrade the performance of the system. Additionally a model of the adversary is used that allows defining spam attack scenario.

2020-03-09
Xie, Yuanpeng, Jiang, Yixin, Liao, Runfa, Wen, Hong, Meng, Jiaxiao, Guo, Xiaobin, Xu, Aidong, Guan, Zewu.  2015.  User Privacy Protection for Cloud Computing Based Smart Grid. 2015 IEEE/CIC International Conference on Communications in China - Workshops (CIC/ICCC). :7–11.

The smart grid aims to improve the efficiency, reliability and safety of the electric system via modern communication system, it's necessary to utilize cloud computing to process and store the data. In fact, it's a promising paradigm to integrate smart grid into cloud computing. However, access to cloud computing system also brings data security issues. This paper focuses on the protection of user privacy in smart meter system based on data combination privacy and trusted third party. The paper demonstrates the security issues for smart grid communication system and cloud computing respectively, and illustrates the security issues for the integration. And we introduce data chunk storage and chunk relationship confusion to protect user privacy. We also propose a chunk information list system for inserting and searching data.

2017-03-08
Yang, K., Forte, D., Tehranipoor, M. M..  2015.  Protecting endpoint devices in IoT supply chain. 2015 IEEE/ACM International Conference on Computer-Aided Design (ICCAD). :351–356.

The Internet of Things (IoT), an emerging global network of uniquely identifiable embedded computing devices within the existing Internet infrastructure, is transforming how we live and work by increasing the connectedness of people and things on a scale that was once unimaginable. In addition to increased communication efficiency between connected objects, the IoT also brings new security and privacy challenges. Comprehensive measures that enable IoT device authentication and secure access control need to be established. Existing hardware, software, and network protection methods, however, are designed against fraction of real security issues and lack the capability to trace the provenance and history information of IoT devices. To mitigate this shortcoming, we propose an RFID-enabled solution that aims at protecting endpoint devices in IoT supply chain. We take advantage of the connection between RFID tag and control chip in an IoT device to enable data transfer from tag memory to centralized database for authentication once deployed. Finally, we evaluate the security of our proposed scheme against various attacks.

2017-02-27
Li, Z., Oechtering, T. J..  2015.  Privacy on hypothesis testing in smart grids. 2015 IEEE Information Theory Workshop - Fall (ITW). :337–341.

In this paper, we study the problem of privacy information leakage in a smart grid. The privacy risk is assumed to be caused by an unauthorized binary hypothesis testing of the consumer's behaviour based on the smart meter readings of energy supplies from the energy provider. Another energy supplies are produced by an alternative energy source. A controller equipped with an energy storage device manages the energy inflows to satisfy the energy demand of the consumer. We study the optimal energy control strategy which minimizes the asymptotic exponential decay rate of the minimum Type II error probability in the unauthorized hypothesis testing to suppress the privacy risk. Our study shows that the cardinality of the energy supplies from the energy provider for the optimal control strategy is no more than two. This result implies a simple objective of the optimal energy control strategy. When additional side information is available for the adversary, the optimal control strategy and privacy risk are compared with the case of leaking smart meter readings to the adversary only.

2016-04-11
Ratliff, Lillian J, Barreto, Carlos, Dong, Roy, Ohlsson, Henrik, Cardenas, Alvaro, Sastry, S Shankar.  2014.  Effects of risk on privacy contracts for demand-side management. arXiv preprint arXiv:1409.7926.

As smart meters continue to be deployed around the world collecting unprecedented levels of fine-grained data about consumers, we need to find mechanisms that are fair to both, (1) the electric utility who needs the data to improve their operations, and (2) the consumer who has a valuation of privacy but at the same time benefits from sharing consumption data. In this paper we address this problem by proposing privacy contracts between electric utilities and consumers with the goal of maximizing the social welfare of both. Our mathematical model designs an optimization problem between a population of users that have different valuations on privacy and the costs of operation by the utility. We then show how contracts can change depending on the probability of a privacy breach. This line of research can help inform not only current but also future smart meter collection practices.

2014-09-17
Huang, Jingwei, Nicol, David M..  2014.  Evidence-based Trust Reasoning. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :17:1–17:2.

Trust is a necessary component in cybersecurity. It is a common task for a system to make a decision about whether or not to trust the credential of an entity from another domain, issued by a third party. Generally, in the cyberspace, connected and interacting systems largely rely on each other with respect to security, privacy, and performance. In their interactions, one entity or system needs to trust others, and this "trust" frequently becomes a vulnerability of that system. Aiming at mitigating the vulnerability, we are developing a computational theory of trust, as a part of our efforts towards Science of Security. Previously, we developed a formal-semantics-based calculus of trust [3, 2], in which trust can be calculated based on a trustor's direct observation on the performance of the trustee, or based on a trust network. In this paper, we construct a framework for making trust reasoning based on the observed evidence. We take privacy in cloud computing as a driving application case [5].

2015-05-05
Lei Xu, Chunxiao Jiang, Jian Wang, Jian Yuan, Yong Ren.  2014.  Information Security in Big Data: Privacy and Data Mining. Access, IEEE. 2:1149-1176.

The growing popularity and development of data mining technologies bring serious threat to the security of individual,'s sensitive information. An emerging research topic in data mining, known as privacy-preserving data mining (PPDM), has been extensively studied in recent years. The basic idea of PPDM is to modify the data in such a way so as to perform data mining algorithms effectively without compromising the security of sensitive information contained in the data. Current studies of PPDM mainly focus on how to reduce the privacy risk brought by data mining operations, while in fact, unwanted disclosure of sensitive information may also happen in the process of data collecting, data publishing, and information (i.e., the data mining results) delivering. In this paper, we view the privacy issues related to data mining from a wider perspective and investigate various approaches that can help to protect sensitive information. In particular, we identify four different types of users involved in data mining applications, namely, data provider, data collector, data miner, and decision maker. For each type of user, we discuss his privacy concerns and the methods that can be adopted to protect sensitive information. We briefly introduce the basics of related research topics, review state-of-the-art approaches, and present some preliminary thoughts on future research directions. Besides exploring the privacy-preserving approaches for each type of user, we also review the game theoretical approaches, which are proposed for analyzing the interactions among different users in a data mining scenario, each of whom has his own valuation on the sensitive information. By differentiating the responsibilities of different users with respect to security of sensitive information, we would like to provide some useful insights into the study of PPDM.

2014-10-24
Hibshi, Hanan, Slavin, Rocky, Niu, Jianwei, Breaux, Travis D.  2014.  Rethinking Security Requirements in RE Research.

As information security became an increasing concern for software developers and users, requirements engineering (RE) researchers brought new insight to security requirements. Security requirements aim to address security at the early stages of system design while accommodating the complex needs of different stakeholders. Meanwhile, other research communities, such as usable privacy and security, have also examined these requirements with specialized goal to make security more usable for stakeholders from product owners, to system users and administrators. In this paper we report results from conducting a literature survey to compare security requirements research from RE Conferences with the Symposium on Usable Privacy and Security (SOUPS). We report similarities between the two research areas, such as common goals, technical definitions, research problems, and directions. Further, we clarify the differences between these two communities to understand how they can leverage each other’s insights. From our analysis, we recommend new directions in security requirements research mainly to expand the meaning of security requirements in RE to reflect the technological advancements that the broader field of security is experiencing. These recommendations to encourage cross- collaboration with other communities are not limited to the security requirements area; in fact, we believe they can be generalized to other areas of RE. 

2015-05-04
Hong Li, Limin Sun, Haojin Zhu, Xiang Lu, Xiuzhen Cheng.  2014.  Achieving privacy preservation in WiFi fingerprint-based localization. INFOCOM, 2014 Proceedings IEEE. :2337-2345.

WiFi fingerprint-based localization is regarded as one of the most promising techniques for indoor localization. The location of a to-be-localized client is estimated by mapping the measured fingerprint (WiFi signal strengths) against a database owned by the localization service provider. A common concern of this approach that has never been addressed in literature is that it may leak the client's location information or disclose the service provider's data privacy. In this paper, we first analyze the privacy issues of WiFi fingerprint-based localization and then propose a Privacy-Preserving WiFi Fingerprint Localization scheme (PriWFL) that can protect both the client's location privacy and the service provider's data privacy. To reduce the computational overhead at the client side, we also present a performance enhancement algorithm by exploiting the indoor mobility prediction. Theoretical performance analysis and experimental study are carried out to validate the effectiveness of PriWFL. Our implementation of PriWFL in a typical Android smartphone and experimental results demonstrate the practicality and efficiency of PriWFL in real-world environments.

Shahare, P.C., Chavhan, N.A..  2014.  An Approach to Secure Sink Node's Location Privacy in Wireless Sensor Networks. Communication Systems and Network Technologies (CSNT), 2014 Fourth International Conference on. :748-751.

Wireless Sensor Network has a wide range of applications including environmental monitoring and data gathering in hostile environments. This kind of network is easily leaned to different external and internal attacks because of its open nature. Sink node is a receiving and collection point that gathers data from the sensor nodes present in the network. Thus, it forms bridge between sensors and the user. A complete sensor network can be made useless if this sink node is attacked. To ensure continuous usage, it is very important to preserve the location privacy of sink nodes. A very good approach for securing location privacy of sink node is proposed in this paper. The proposed scheme tries to modify the traditional Blast technique by adding shortest path algorithm and an efficient clustering mechanism in the network and tries to minimize the energy consumption and packet delay.

2015-05-06
Adjei, J.K..  2014.  Explaining the Role of Trust in Cloud Service Acquisition. Mobile Cloud Computing, Services, and Engineering (MobileCloud), 2014 2nd IEEE International Conference on. :283-288.

Effective digital identity management system is a critical enabler of cloud computing, since it supports the provision of the required assurances to the transacting parties. Such assurances sometimes require the disclosure of sensitive personal information. Given the prevalence of various forms of identity abuses on the Internet, a re-examination of the factors underlying cloud services acquisition has become critical and imperative. In order to provide better assurances, parties to cloud transactions must have confidence in service providers' ability and integrity in protecting their interest and personal information. Thus a trusted cloud identity ecosystem could promote such user confidence and assurances. Using a qualitative research approach, this paper explains the role of trust in cloud service acquisition by organizations. The paper focuses on the processes of acquisition of cloud services by financial institutions in Ghana. The study forms part of comprehensive study on the monetization of personal Identity information.

Adjei, J.K..  2014.  Explaining the Role of Trust in Cloud Service Acquisition. Mobile Cloud Computing, Services, and Engineering (MobileCloud), 2014 2nd IEEE International Conference on. :283-288.

Effective digital identity management system is a critical enabler of cloud computing, since it supports the provision of the required assurances to the transacting parties. Such assurances sometimes require the disclosure of sensitive personal information. Given the prevalence of various forms of identity abuses on the Internet, a re-examination of the factors underlying cloud services acquisition has become critical and imperative. In order to provide better assurances, parties to cloud transactions must have confidence in service providers' ability and integrity in protecting their interest and personal information. Thus a trusted cloud identity ecosystem could promote such user confidence and assurances. Using a qualitative research approach, this paper explains the role of trust in cloud service acquisition by organizations. The paper focuses on the processes of acquisition of cloud services by financial institutions in Ghana. The study forms part of comprehensive study on the monetization of personal Identity information.

Ahmad, A., Hassan, M.M., Aziz, A..  2014.  A Multi-token Authorization Strategy for Secure Mobile Cloud Computing. Mobile Cloud Computing, Services, and Engineering (MobileCloud), 2014 2nd IEEE International Conference on. :136-141.

Cloud computing is an emerging paradigm shifting the shape of computing models from being a technology to a utility. However, security, privacy and trust are amongst the issues that can subvert the benefits and hence wide deployment of cloud computing. With the introduction of omnipresent mobile-based clients, the ubiquity of the model increases, suggesting a still higher integration in life. Nonetheless, the security issues rise to a higher degree as well. The constrained input methods for credentials and the vulnerable wireless communication links are among factors giving rise to serious security issues. To strengthen the access control of cloud resources, organizations now commonly acquire Identity Management Systems (IdM). This paper presents that the most popular IdM, namely OAuth, working in scope of Mobile Cloud Computing has many weaknesses in authorization architecture. In particular, authors find two major issues in current IdM. First, if the IdM System is compromised through malicious code, it allows a hacker to get authorization of all the protected resources hosted on a cloud. Second, all the communication links among client, cloud and IdM carries complete authorization token, that can allow hacker, through traffic interception at any communication link, an illegitimate access of protected resources. We also suggest a solution to the reported problems, and justify our arguments with experimentation and mathematical modeling.

2015-05-04
Novak, E., Qun Li.  2014.  Near-pri: Private, proximity based location sharing. INFOCOM, 2014 Proceedings IEEE. :37-45.

As the ubiquity of smartphones increases we see an increase in the popularity of location based services. Specifically, online social networks provide services such as alerting the user of friend co-location, and finding a user's k nearest neighbors. Location information is sensitive, which makes privacy a strong concern for location based systems like these. We have built one such service that allows two parties to share location information privately and securely. Our system allows every user to maintain and enforce their own policy. When one party, (Alice), queries the location of another party, (Bob), our system uses homomorphic encryption to test if Alice is within Bob's policy. If she is, Bob's location is shared with Alice only. If she is not, no user location information is shared with anyone. Due to the importance and sensitivity of location information, and the easily deployable design of our system, we offer a useful, practical, and important system to users. Our main contribution is a flexible, practical protocol for private proximity testing, a useful and efficient technique for representing location values, and a working implementation of the system we design in this paper. It is implemented as an Android application with the Facebook online social network used for communication between users.

Ming Chen, Wenzhong Li, Zhuo Li, Sanglu Lu, Daoxu Chen.  2014.  Preserving location privacy based on distributed cache pushing. Wireless Communications and Networking Conference (WCNC), 2014 IEEE. :3456-3461.


Location privacy preservation has become an important issue in providing location based services (LBSs). When the mobile users report their locations to the LBS server or the third-party servers, they risk the leak of their location information if such servers are compromised. To address this issue, we propose a Location Privacy Preservation Scheme (LPPS) based on distributed cache pushing which is based on Markov Chain. The LPPS deploys distributed cache proxies in the most frequently visited areas to store the most popular location-related data and pushes them to mobile users passing by. In the way that the mobile users receive the popular location-related data from the cache proxies without reporting their real locations, the users' location privacy is well preserved, which is shown to achieve k-anonymity. Extensive experiments illustrate that the proposed LPPS achieve decent service coverage ratio and cache hit ratio with low communication overhead.
 

Wiesner, K., Feld, S., Dorfmeister, F., Linnhoff-Popien, C..  2014.  Right to silence: Establishing map-based Silent Zones for participatory sensing. Intelligent Sensors, Sensor Networks and Information Processing (ISSNIP), 2014 IEEE Ninth International Conference on. :1-6.

Participatory sensing tries to create cost-effective, large-scale sensing systems by leveraging sensors embedded in mobile devices. One major challenge in these systems is to protect the users' privacy, since users will not contribute data if their privacy is jeopardized. Especially location data needs to be protected if it is likely to reveal information about the users' identities. A common solution is the blinding out approach that creates so-called ban zones in which location data is not published. Thereby, a user's important places, e.g., her home or workplace, can be concealed. However, ban zones of a fixed size are not able to guarantee any particular level of privacy. For instance, a ban zone that is large enough to conceal a user's home in a large city might be too small in a less populated area. For this reason, we propose an approach for dynamic map-based blinding out: The boundaries of our privacy zones, called Silent Zones, are determined in such way that at least k buildings are located within this zone. Thus, our approach adapts to the habitat density and we can guarantee k-anonymity in terms of surrounding buildings. In this paper, we present two new algorithms for creating Silent Zones and evaluate their performance. Our results show that especially in worst case scenarios, i.e., in sparsely populated areas, our approach outperforms standard ban zones and guarantees the specified privacy level.

2015-05-05
Manandhar, K., Adcock, B., Xiaojun Cao.  2014.  Preserving the Anonymity in MobilityFirst networks. Computer Communication and Networks (ICCCN), 2014 23rd International Conference on. :1-6.

A scheme for preserving privacy in MobilityFirst (MF) clean-slate future Internet architecture is proposed in this paper. The proposed scheme, called Anonymity in MobilityFirst (AMF), utilizes the three-tiered approach to effectively exploit the inherent properties of MF Network such as Globally Unique Flat Identifier (GUID) and Global Name Resolution Service (GNRS) to provide anonymity to the users. While employing new proposed schemes in exchanging of keys between different tiers of routers to alleviate trust issues, the proposed scheme uses multiple routers in each tier to avoid collaboration amongst the routers in the three tiers to expose the end users.

2015-05-04
Rahman, S.M.M., Kamruzzaman, S.M., Almogren, A., Alelaiwi, A., Alamri, A., Alghamdi, A..  2014.  Anonymous and Secure Communication Protocol for Cognitive Radio Ad Hoc Networks. Multimedia (ISM), 2014 IEEE International Symposium on. :393-398.

Cognitive radio (CR) networks are becoming an increasingly important part of the wireless networking landscape due to the ever-increasing scarcity of spectrum resources throughout the world. Nowadays CR media is becoming popular wireless communication media for disaster recovery communication network. Although the operational aspects of CR are being explored vigorously, its security aspects have gained less attention to the research community. The existing research on CR network mainly focuses on the spectrum sensing and allocation, energy efficiency, high throughput, end-to-end delay and other aspect of the network technology. But, very few focuses on the security aspect and almost none focus on the secure anonymous communication in CR networks (CRNs). In this research article we would focus on secure anonymous communication in CR ad hoc networks (CRANs). We would propose a secure anonymous routing for CRANs based on pairing based cryptography which would provide source node, destination node and the location anonymity. Furthermore, the proposed research would protect different attacks those are feasible on CRANs.

Jagdale, B.N., Bakal, J.W..  2014.  Synergetic cloaking technique in wireless network for location privacy. Industrial and Information Systems (ICIIS), 2014 9th International Conference on. :1-6.

Mobile users access location services from a location based server. While doing so, the user's privacy is at risk. The server has access to all details about the user. Example the recently visited places, the type of information he accesses. We have presented synergetic technique to safeguard location privacy of users accessing location-based services via mobile devices. Mobile devices have a capability to form ad-hoc networks to hide a user's identity and position. The user who requires the service is the query originator and who requests the service on behalf of query originator is the query sender. The query originator selects the query sender with equal probability which leads to anonymity in the network. The location revealed to the location service provider is a rectangle instead of exact co-ordinate. In this paper we have simulated the mobile network and shown the results for cloaking area sizes and performance against the variation in the density of users.