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Toward equitable investment in transport infrastructures: Providing a comparative framework based on theories of justice
, Article Middle - East Journal of Scientific Research ; Vol. 19, issue. 9 , 2014 , pp. 1215-1225 ; ISSN: 19909233 ; Nazari, S ; Jahromi, H. N ; Sharif University of Technology
Abstract
Equity in distribution is one of the most controversial and essential concepts which for a long time has been the central concern of political philosophers when considering planning concerns of the societies. Transport is a key field by which politicians and decision-makers impose their intention on societies. Although there have been studies discussing equity in transport, yet there is no clear mathematical framework to utilize the equity concept in transportation planning. This study has reviewed equity in transportation, as well as in human science studies to investigate and determine how transportation advantages should be equitably distributed among society members. This review has led...
New methods for Opportunistic Spectrum Access in Multi-user Cognitive Radio Networks
, M.Sc. Thesis Sharif University of Technology ; Pakravan, Mohammad Reza (Supervisor)
Abstract
In this dissertation, we design channel access strategies for opportunistic spectrum access in cognitive radio networks. It is assumed that the secondary transmitter and receiver hop across spectrum opportunities synchronously. This synchronization between the transmitter and the receiver can be separated in two phases: In the first phase, two Secondary Users (SUs) meet each other for the first time in a spectrum opportunity and exchange control messages. In the second phase, two SUs hop across available channels to transfer data. Rendezvous algorithm can facilitate the first meeting of two SUs. For the first phase, we propose a blind rendezvous algorithm and study its features. We show that...
Missing a trusted reference monitor: How to enforce confidential and dynamic access policies?
, Article Communications in Computer and Information Science ; Vol. 428, issue , Oct , 2014 , p. 92-104 ; ISSN: 18650929 ; ISBN: 978-3319109022 ; Javadi, S. A ; Hadavi, M. A ; Jalili1, R ; Sharif University of Technology
Abstract
Popularity of data outsourcing and its consequent access control issues such as dynamism and efficiency is the main motivation of this paper. Existing solutions suffer from the potential unlimited number of user keys, inefficient update of policies, and disclosure of data owner’s access control policies. Using Chinese remainder theorem and proxy re-encryption together, in this paper, we propose an efficient access control enforcement mechanism based on selective encryption that addresses all the shortages. The overall architecture, required algorithms, and access control policy update are discussed. The mechanism is evaluated through simulation and, the given results are satisfactory
A periodic jump-based rendezvous algorithm in cognitive radio networks
, Article Computer Communications ; Volume 79, 1 , April , 2016 , Pages 66–77 ; 01403664 (ISSN) ; Pakravan, M. R ; Sharif University of Technology
Elsevier
2016
Abstract
An important issue in designing multichannel MAC protocols for Opportunistic Spectrum Access (OSA) is the synchronization between Secondary Users (SUs). Synchronization can be performed in two phases: the initial handshaking, and then the synchronous hopping across available channels. In this paper, we address the problem of initial handshaking through the approach called "blind rendezvous". We first introduce a role-based solution by constructing two channel hopping sequences. The secondary transmitter and receiver jump across channels according to these two sequences. The proposed algorithm guarantees rendezvous in at most (C+1)2 time slots (where C is the number of channels) and two SUs...
Enforcing access control policies over data stored on untrusted server
, Article 2017 14th International ISC (Iranian Society of Cryptology) Conference on Information Security and Cryptology, ISCISC 2017, 6 September 2017 through 7 September 2017 ; 2018 , Pages 54-57 ; 9781538665602 (ISBN) ; Jalili, R ; Sharif University of Technology
Abstract
One of the security issues in data outsourcing scenario is the enforcement of data owner's access control policies. This includes some challenges; namely, the number of keys required to access authorized resources, efficient policy updating, write access control enforcement, user and data owner overhead, and preserving confidentiality of data and policies. Most of the existing solutions address only some of the challenges, while they impose high overhead on both the data owner and users. Though, policy management in the Role-Based Access Control (RBAC) model is easier and more efficient due to the existence of role hierarchical structure and role inheritance; most of the existing solutions...
An anonymous attribute-based access control system supporting access structure update
, Article 16th International ISC (Iranian Society of Cryptology) Conference on Information Security and Cryptology, ISCISC 2019, 28 August 2019 through 29 August 2019 ; 2019 , Pages 85-91 ; 9781728143736 (ISBN) ; Ali, M ; Mohajeri, J ; Aref, M. R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
It is quite common nowadays for clients to outsource their personal data to a cloud service provider. However, it causes some new challenges in the area of data confidentiality and access control. Attribute-based encryption is a promising solution for providing confidentiality and fine-grained access control in a cloud-based cryptographic system. Moreover, in some cases, to preserve the privacy of clients and data, applying hidden access structures is required. Also, a data owner should be able to update his defined access structure at any time when he is online or not. As in several real-world application scenarios like e-health systems, the anonymity of recipients, and the possibility of...
A Study in Bound of Graph and Generalized Access Structures
, M.Sc. Thesis Sharif University of Technology ; khazaei, Shahram (Supervisor)
Abstract
Determining the value of optimal information ratio for a given access structure and finding the upper and lower bounds for the information ratio in secreet sharing is one of the main problems that has been studied over time. In this thesis, we have tried to introduce the tools used in this field, including polymatroids and Shannon’s inequalities, linear programming, decomposition and etc, examine the papers presented in this field and rewrite obtained results in a simpler way
Access control aware data retrieval for secret sharing based database outsourcing
, Article Distributed and Parallel Databases ; Volume 34, Issue 4 , Dec , 2015 , pp 505–534 ; 09268782 (ISSN) ; Jalili, R ; Karimi, L ; Sharif University of Technology
Kluwer Academic Publishers
2015
Abstract
Enforcing dynamic and confidential access control policies is a challenging issue of data outsourcing to external servers due to the lack of trust towards the servers. In this paper, we propose a scalable yet flexible access control enforcement mechanism when the underlying relational data, on which access policies are defined, has been shared through a secret sharing scheme. For sharing values of an attribute in a relation, the attribute is assigned a secret distribution key and its values are split and distributed among data servers according to a Shamir based secret sharing scheme. Given access control policies over attributes of the relation schema, access to distribution keys, used...
Deterministic multiple access wiretap channel
, Article Proceedings 2010 IEEE International Conference on Information Theory and Information Security, ICITIS 2010, 17 December 2010 through 19 December 2010, Beijing ; 2010 , Pages 998-1001 ; 9781424469406 (ISBN) ; Salimi, S ; Salmasizadeh, M ; Sharif University of Technology
2010
Abstract
Two-user Multiple Access Channel with a Wire- Tapper (MAC-WT) is considered. A general outer bound for the secrecy capacity region is given. Also, we have defined the Deterministic MAC-WT, where the channel input of each user is a deterministic function of the channel output and the channel input of the other user. For this network single-letter inner and outer bounds for the secrecy capacity region are given. Furthermore, it is shown that in the Deterministic MAC-WT, if the wiretapper channel is a degraded version of the main channel, inner and outer bounds meet and the secrecy capacity region is characterized
Access control aware data retrieval for secret sharing based database outsourcing
, Article Distributed and Parallel Databases ; Volume 34, Issue 4 , 2016 , Pages 505-534 ; 09268782 (ISSN) ; Jalili, R ; Karimi, L ; Sharif University of Technology
Springer New York LLC
2016
Abstract
Enforcing dynamic and confidential access control policies is a challenging issue of data outsourcing to external servers due to the lack of trust towards the servers. In this paper, we propose a scalable yet flexible access control enforcement mechanism when the underlying relational data, on which access policies are defined, has been shared through a secret sharing scheme. For sharing values of an attribute in a relation, the attribute is assigned a secret distribution key and its values are split and distributed among data servers according to a Shamir based secret sharing scheme. Given access control policies over attributes of the relation schema, access to distribution keys, used...
Sensitivity analysis of coherent ultrashort light pulse CDMA communication system with respect to dispersion
, Article Optical Transmission, Switching, and Subsystems V, Wuhan, 2 November 2007 through 5 November 2007 ; Volume 6783 , 2007 ; 0277786X (ISSN); 9780819469465 (ISBN) ; Jamshidi, K ; Salehi, J. A ; Sharif University of Technology
2007
Abstract
In this paper, we analyze the sensitivity degradation of a system due to various orders of chromatic dispersion. To do this, the power penalty of the uncoded and encoded pulse of a coherent ultrashort light pulse Code Division Multiple Access (CDMA) communication system due to various orders of chromatic dispersions are analyzed. Analysis of uncoded pulse shows that the power penalty is unacceptably high when second order dispersion is not compensated. However we can obtain acceptable level of power penalties while compensating second and third order dispersion. Also, due to the high order of dispersion, the power of encoded pulse decreases as it propagates through the fiber which leads to a...
Context-aware provisional access control
, Article 2nd International Conference on Information Systems Security, ICISS 2006, 19 December 2006 through 21 December 2006 ; Volume 4332 LNCS , 2006 , Pages 132-146 ; 03029743 (ISSN); 9783540689621 (ISBN) ; Amini, M ; Jalili, R ; Sharif University of Technology
Springer Verlag
2006
Abstract
High heterogeneity and dynamicity of pervasive computing environments introduces requirement of more flexible and functional access control policies. The notion of provisional actions has been defined previously to overcome the insufficient grant/denial response to an access request and has been incorporated in the provision-based access controlmodel(PBAC).BasedonPBAC,weproposeacontext-aware provision-based access control model, capable of dynamic adaptation of access control policy according to the changing context. In particular, the model facilitates the definition of context-aware policies and enriches the access control by enforcing provisional actions in addition to common permissions....
Confidential Access to the Outsourced Relational Data
, M.Sc. Thesis Sharif University of Technology ; Jalili, Rasool (Supervisor)
Abstract
In recent years, there has been a trend toward outsourcing data to the cloud provider. These companies must tackle the data security challenges. Generally these parties are assumed to be honest but curious. In past years, the research communities have been investigating different solution to ensure confidentiality.
In addition to data confidentiality access and pattern confidentiality is a high-priority issue in some cases so. potential adversary should be unable to drive information from the observed access pattern to the outsourced data. Despite the fact that there are more investigation in the field of data confidentiality, concern over data security are the rise in outsourcing data,...
In addition to data confidentiality access and pattern confidentiality is a high-priority issue in some cases so. potential adversary should be unable to drive information from the observed access pattern to the outsourced data. Despite the fact that there are more investigation in the field of data confidentiality, concern over data security are the rise in outsourcing data,...
On the performance of spectrally-encoded spread-time ultrawideband CDMA communication systems [electronic resource]
, Article IEEE Transactions on Wireless Communications ; 2008 Vol. 7, No. 11 ; Salehi, J. A ; Sharif University Of Technology
Abstract
In this paper we study the performance of spectrally-encoded spread-time (SE/ST) technique when applied to ultrawideband (UWB) signals in the context of wireless code-division multiple-access (CDMA) communication. In this technique UWB pulses are spectrally encoded with pseudorandom codes that are assigned uniquely to each user. We shall show that the SE/ST ultrawideband system provides an appropriate multi-user capacity in realistic UWB channels, along with the ability of narrowband interference (NBI) suppression. To this end, after obtaining a suitable statistical model for spectrally encoded spread-time signals, we investigate the performance of the system in the presence of...
Efficient modulation technique for optical code division multiple access networks: Differential pulse position modulation
, Article IET Optoelectronics ; Vol. 8, issue. 5 , 2014 , p. 181-190 ; Shoaie, M. A ; Pakravan, M. R ; Sharif University of Technology
Abstract
In this study, the authors study a fibre-optic local area network deploying optical code division multiple access technique with differential M-ary pulse position modulation (DPPM). The authors present the performance analysis of DPPM signalling using a double optical hardlimiter receiver structure considering the impairment caused by interference of other users. The analysis assumes a set of bit asynchronous transmitters employing generalised optical orthogonal codes for their DPPM signalling (GOOC-DPPM). Using mathematical analysis and simulations, the authors have demonstrated that GOOCDPPM improves both frame error probability and the maximum achievable network throughput compared with...
Overview of MAC protocols for energy harvesting wireless sensor networks
, Article IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 30 August 2015 through 2 September 2015 ; Volume 2015-December , 2015 , Pages 2032-2037 ; 9781467367820 (ISBN) ; Pakravan, M. R ; Sharif University of Technology
Abstract
Wireless Sensor Networks (WSNs) have been weaved into the fabric of our daily lives. The foremost impediment in the rapid development of these networks is the energy limitation which inhibits them from meeting specific application requirements. Recently, the advances in energy harvesting technology have made it possible to replenish the energy of sensors via external sources. Energy Harvesting-Wireless Sensor Networks (EH-WSNs) are being transformed from a visionary concept into reality. However, this concept is still in its infancy and calls for extensive research to cater to the needs of WSNs. For future progress of EH-WSNs, Medium Access Control (MAC) layer has undoubtedly a decisive role...
Specification of history based constraints for access control in conceptual level
, Article Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), 17 December 2010 through 19 December 2010, Gandhinagar ; Volume 6503 LNCS , 2010 , Pages 186-200 ; 03029743 (ISSN) ; 9783642177132 (ISBN) ; Amini, M ; Jalili, R ; Sharif University of Technology
2010
Abstract
An access control model for Semantic Web should take the semantic relationships among the entities, defined in the abstract conceptual level (i.e., ontology level), into account. Authorization and policy specification based on a logical model let us infer implicit security policies from the explicit ones based on the defined semantic relationships in the domains of subjects, objects, and actions. In this paper, we propose a logic based access control model for specification and inference of history-constrained access policies in conceptual level of Semantic Web. The proposed model (named TDLBAC-2) enables authorities to state policy rules based on the history of users' accesses using a...
Single-quantum interferometry: Which-way versus which-phase information stored in an ancillary quantum system
, Article Journal of Physics A: Mathematical and Theoretical ; Volume 52, Issue 40 , 2019 ; 17518113 (ISSN) ; Bahrampour, A. R ; Sharif University of Technology
Institute of Physics Publishing
2019
Abstract
In interferometers, the more information about a quantum's path that is available in an ancillary quantum system (AQS), the less visibility the interference has. By use of Shannon entropy, we try to compare the amount of which-phase information with the amount of which-way information stored in the AQS of two-path interferometers with symmetric beam merging. We show that the former is less than or equal to the latter if the bipartite system of the single quantum and the AQS is initially prepared in a pure state and the interaction between the two parts is unitary. The equality holds when symmetry exists. No which-way information is obtained by the measurement that we use for extracting the...
A context-aware access control model for pervasive computing environments
, Article 2007 International Conference on Intelligent Pervasive Computing, IPC 2007, Jeju Island, 11 October 2007 through 13 October 2007 ; 2007 , Pages 51-56 ; 0769530060 (ISBN); 9780769530062 (ISBN) ; Amini, M ; Zokaei, S ; Sharif University of Technology
2007
Abstract
In pervasive computing environments, a user can access resources and services from any where and at any time; thus a key security challenge in these environments is the design of an effective access control model which is aware of context modifications. Changes in context may trigger changes in authorizations. In this paper, we propose a new context-aware access control model based on role-based access control model for pervasive computing environments. We assign roles to users dynamically based on the long-term context information and tune active role's permissions according to the short-term context information of the users and environment. © 2007 IEEE
Web graph compression by edge elimination
, Article Data Compression Conference, DCC 2006, Snowbird, UT, 28 March 2006 through 30 March 2006 ; 2006 , Pages 459- ; 10680314 (ISSN) ; Khalili, H ; Nourbakhsh, E ; Ghodsi, M ; Brandeis University ; Sharif University of Technology
2006