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10th Symposium on Abstraction, Reformulation, and Approximation, SARA 2013

作者： Van Seijen, Harm Whiteson, Shimon Kester, Leon Department of Computing Science University of Alberta Edmonton Canada Informatics Institute University of Amsterdam Amsterdam Netherlands Distributed Sensor Systems Group TNO Defence Security and Safety The Hague Netherlands

ISBN: (纸本)9781577356301

This paper introduces a novel approach for abstraction selection in reinforcement learning problems modelled as factored Markov decision processes (MDPs), for which a state is described via a set of state components. In abstraction selection, an agent must choose an abstraction from a set of candidate abstractions, each build up from a different combination of state components. Copyright © 2013 Association for the Advancement of Artificial Intelligence.

关键词： Reinforcement learning

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Selective cloaking: Need-to-know for location-based apps

Selective cloaking: Need-to-know for location-based apps

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Annual Conference on Privacy, security and Trust, PST

作者： Benjamin Henne Christian Kater Matthew Smith Michael Brenner Distributed Computing & Security Group Leibniz Universität Hannover Germany

ISBN: (纸本)9781467358378

Currently location privacy settings of mobile operating systems are limited to the option of enabling or disabling the use of location completely or on a per-app basis. When location use is allowed, users always reveal their location in full precision even to apps that do not need it. For instance, weather forecast apps and navigation apps both get the most exact location a device can determine. Up to now, mobile privacy research was focused on the recognition and prevention of disclosure of private data. This includes location data, but does not extend to privacy in use cases where users do want to disclose their location - but not in full detail. However, the increasing adoption of smartphones entails the increasing use of location-based services as well. Users want to use these services, but have privacy concerns. As many location-based services do not require exact locations, user privacy can be increased by only disclosing location in such detail as required for the respective service to function. To enable users to restrict the accuracy of location data that is revealed to apps, we created a location privacy framework that allows per-app location obfuscation. The framework allows easy integration of different obfuscation algorithms into the Android system. We present both on-device obfuscation and service-based obfuscation and evaluate our framework.

关键词： Privacy Androids Humanoid robots Data privacy Mobile communication Databases Cryptography

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WAHC 2013: Workshop on Applied Homomorphic Cryptography

Lecture Notes in Computer Science (including subseries Lectu...

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Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 2013年 7862 LNCS卷 VIII页

作者： Brenner, Michael Smith, Matthew Leibniz Universität Hannover Distributed Computing and Security Group Schloßwender Straße 5 30159 Hanover Germany

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TrustSplit: Usable confidentiality for social network messaging 12

TrustSplit: Usable confidentiality for social network messag...

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23rd ACM Conference on Hypertext and Social Media, HT'12

作者： Fahl, Sascha Harbach, Marian Muders, Thomas Smith, Matthew Leibniz University of Hannover Distributed Computing and Security Group Hannover Germany

ISBN: (纸本)9781450313353

It is well known that online social networking sites (OSNs) such as Facebook pose risks to their users' privacy. OSNs store vast amounts of users' private data and activities and therefore subject the user to the risk of undesired disclosure. The regular non tech-savvy Facebook user either has little awareness of his privacy needs or is not willing or capable to invest much extra effort into securing his online activities. In this paper, we present a non-disruptive and easy to-use service that helps to protect users' most private information, namely their private messages and chats against the OSN provider itself and external adversaries. Our novel Confidentiality as a Service paradigm was designed with usability and non-obtrusiveness in mind and requires little to no additional knowledge on the part of the users. The simplicity of the service is achieved through a novel trust splitting approach integrated into the Confidentiality as a Service paradigm. To show the feasibility of our approach we present a fully-working prototype for Facebook and an initial usability study. All of the participating subjects completed the study successfully without any problems or errors and only required three minutes on average for the entire installation and setup procedure. Copyright 2012 ACM.

关键词： Social networking (online)

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All our messages are belong to us: Usable confidentiality in social networks

All our messages are belong to us: Usable confidentiality in...

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21st Annual Conference on World Wide Web, WWW'12

作者： Harbach, Marian Fahl, Sascha Muders, Thomas Smith, Matthew Distributed Computing and Security Group Leibniz University of Hannover Hannover Germany

ISBN: (纸本)9781450312301

Current online social networking (OSN) sites pose severe risks to their users' privacy. Facebook in particular is capturing more and more of a user's past activities, sometimes starting from the day of birth. Instead of transiently passing on information between friends, a user's data is stored persistently and therefore subject to the risk of undesired disclosure. Traditionally, a regular user of a social network has little awareness of her privacy needs in the Web or is not ready to invest a considerable effort in securing her online activities. Furthermore, the centralised nature of proprietary social networking platforms simply does not cater for end-to-end privacy protection mechanisms. In this paper, we present a non-disruptive and lightweight integration of a confidentiality mechanism into OSNs. Additionally, direct integration of visual security indicators into the OSN UI raise the awareness for (un)protected content and thus their own privacy. We present a fully-working prototype for Facebook and an initial usability study, showing that, on average, untrained users can be ready to use the service in three minutes. Copyright is held by the author/owner(s).

关键词： Data privacy

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Practical applications of homomorphic encryption

Practical applications of homomorphic encryption

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International Conference on security and Cryptography, SECRYPT 2012

作者： Brenner, Michael Perl, Henning Smith, Matthew Distributed Computing Security Group Leibniz Universitt Hannover Hannover Germany

ISBN: (纸本)9789898565242

Homomorphic cryptography has been one of the most interesting topics of mathematics and computer security since Gentry presented the first construction of a fully homomorphic encryption (FHE) scheme in 2009. Since then, a number of different schemes have been found, that follow the approach of bootstrapping a fully homomorphic scheme from a somewhat homomorphic foundation. All existing implementations of these systems clearly proved, that fully homomorphic encryption is not yet practical, due to significant performance limitations. However, there are many applications in the area of secure methods for cloud computing, distributed computing and delegation of computation in general, that can be implemented with homomorphic encryption schemes of limited depth. We discuss a simple algebraically homomorphic scheme over the integers that is based on the factorization of an approximate semiprime integer. We analyze the properties of the scheme and provide a couple of known protocols that can be implemented with it. We also provide a detailed discussion on searching with encrypted search terms and present implementations and performance figures for the solutions discussed in this paper.

关键词： distributed computer systems

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How practical is homomorphically encrypted program execution? An implementation and performance evaluation

How practical is homomorphically encrypted program execution...

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11th IEEE International Conference on Trust, security and Privacy in computing and Communications, TrustCom-2012

作者： Brenner, Michael Perl, Henning Smith, Matthew Distributed Computing Security Group Leibniz Universität Hannover Germany

ISBN: (纸本)9780769547459

Homomorphic cryptography has received a lot of attention due to potentially ground breaking advances in cryptography. However it is also surrounded by a lot of hyperbole such as "ground breaking advances", "this will solve all Cloud computing problems" to "it is completely impractical" and "it will never work for real world problems". In previous work we showed how homomorphic encryption can be used to execute arbitrary programs in encrypted space, showing that at least in theory real world problems can be computed protected by homomorphic cryptography without losing generality. In this paper we expand our work to evaluate how practical current homomorphic cryptography based on the Smart-Vercauteren system is for executing arbitrary programs on untrusted resources. For this we present the implementation of a method to compute non-linear secret programs on an untrusted resource using encrypted circuits embedded in an encrypted virtual machine. We successively show how a processor architecture using encrypted circuits can be implemented so it can support read and write memory access, dynamic parameters and non-linear programs that render branch-decisions at runtime. The system comprises the runtime environment for program execution and an assembler to generate the encrypted machine code. We present performance evaluation of the sub-components as well as the complete system. The system represents a flexible prototype for homomorphic program execution in software and system architecture. © 2012 IEEE.

关键词： Cryptography

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Mobile evil twin malnets - The worst of both worlds

Mobile evil twin malnets - The worst of both worlds

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11th International Conference on Cryptology and Network security, CANS 2012

作者： Szongott, Christian Henne, Benjamin Smith, Matthew Distributed Computing and Security Group Gottfried Wilhelm Leibniz University of Hannover Germany

ISBN: (纸本)9783642354038

The mobile computing world is undergoing major changes both in the capability as well as in the proliferation of mobile devices. While, up to now, mobile malware has played a relatively small role compared to the behemoth of desktop malware, the changing environment is steadily increasing the attractiveness of mobile devices as exploitable resources. The increased usage and connectivity of mobile devices opens up a much larger set of attack vectors to compromise them. In this paper, we adapt the evil twin rogue access point attack to the mobile domain and show how it can be used to create a mobile malnet, which is capable of spreading epidemically. We implemented the key components of the concept for the iPhone to study its properties in a laboratory environment. To demonstrate the dangers which come along with this kind of attack we simulate a metropolitan area and show how fast a malware can spread in a mobile environment. © Springer-Verlag 2012.

关键词： Malware

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Evaluating the threat of epidemic mobile malware

Evaluating the threat of epidemic mobile malware

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2012 IEEE 8th International Conference on Wireless and Mobile computing, Networking and Communications, WiMob 2012

作者： Szongott, Christian Henne, Benjamin Smith, Matthew Distributed Computing and Security Group Gottfried Wilhelm Leibniz University of Hannover Germany

ISBN: (纸本)9781467314305

While mobile malware has played a relatively small role compared to the behemoth of desktop malware, the changes both in the capability as well as in the proliferation of the mobile devices will steadily increase the attractiveness of mobile devices as resources to be attacked. The increased usage and connectivity of mobile devices opens up a much larger set of attack vectors to compromise these devices. In this paper, we discuss how the new features of mobile devices opens up the capability to create a new generation of mobile malware which is capable of realistically spreading epidemically on a fully mobile infection vector. We present a prototype of such a mobile malware that uses these features to replicate itself and spread over a mobile device-to-device vector. Using simulations we give quantitative support for the number of mobile devices and conditions needed to for an epidemic spread of mobile malware and present infection scenarios in downtown Chicago. Our results show that the recent growth and market dominance of just a handful of mobile phone companies and the trend towards mobile operating systems monoculture has already created a viable substrate for epidemic mobile malware. © 2012 IEEE.

关键词： Malware

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Towards privacy-preserving access control with hidden policies, hidden credentials and hidden decisions

Towards privacy-preserving access control with hidden polici...

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2012 10th Annual International Conference on Privacy, security and Trust, PST 2012

作者： Harbach, Marian Fahl, Sascha Brenner, Michael Muders, Thomas Smith, Matthew Distributed Computing and Security Group Leibniz University Hannover Schloßwender Str. 5 30159 Hannover Germany

ISBN: (纸本)9781467323260

The growing adoption of cloud technology in sensitive application domains, such as medicine, gives rise to new problems in maintaining the privacy of the involved parties during authorisation. In such domains, an honest but curious service provider can derive sensitive information purely from the authorisation process. In this paper, we present a detailed discussion of this rising problem including a concrete example and argue the need for the combination of hidden credentials, hidden policies and hidden decisions. We then show that mechanisms explored in previous work only cover individual aspects of this problem, but do not achieve a comprehensive solution without making restrictive assumptions on the resources, policies or subjects to be protected. As a first step towards solving this problem, we introduce an abstract foundation for using homomorphic cryptography to provide the required combination of privacy as a wrapper for other access control (AC) mechanisms. We achieve hidden policies, hidden credentials and even hidden access control decisions, so that the subject of an AC request only learns whether or not access was granted. Meanwhile, the provider of a resource learns nothing at the policy decision point and only access frequencies for individual resources at the policy enforcement point. We postulate that this is the maximum achievable level of protection in the authorisation process, without making restrictive assumptions on the resources, policies or subjects to be protected. Once homomorphic cryptography achieves satisfactory performance, our model can be used to transparently add this protection to other access control models. © 2012 IEEE.

关键词： Problem solving

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