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Using Guesswork as a Measure for Confidentiality of Selectively Encrypted Messages
Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. (Datavetenskap)
Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. (Datavetenskap)
Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. (Datavetenskap)
Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT. (Datavetenskap)
2006 (English)In: Quality of Protection: Security Measurements and Metrics / [ed] Dieter Gollmann, Fabio Massacci and Artsiom Yautsiukhin, Boston: Springer, 2006, 173-184 p.Chapter in book (Refereed)
Abstract [en]

n this paper, we start to investigate the security implications of selective encryption. We do this by using the measure guesswork, which gives us the expected number of guesses that an attacker must perform in an optimal brute force attack to reveal an encrypted message. The characteristics of the proposed measure are investigated for zero-order languages. We also introduce the concept of reduction chains to describe how the message (or rather search) space changes for an attacker with different levels of encryption.

Place, publisher, year, edition, pages
Boston: Springer, 2006. 173-184 p.
Series
Advances in Information Security, ISSN 1568-2633 ; 23-4
National Category
Computer Systems
Research subject
Computer Science
Identifiers
URN: urn:nbn:se:kau:diva-1915DOI: 10.1007/978-0-387-36584-8_14OAI: oai:DiVA.org:kau-1915DiVA: diva2:5014
Available from: 2007-10-09 Created: 2007-10-09 Last updated: 2012-09-04Bibliographically approved
In thesis
1. Towards Measurable and Tunable Security
Open this publication in new window or tab >>Towards Measurable and Tunable Security
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Many security services today only provides one security configuration at run-time, and cannot then utilize the trade-off between performance and security. In order to make use of this trade-off, tunable security services providing several security configurations that can be selected at run-time are needed. To be able to make intelligent choices on which security configuration to use for different situations we need to know how good they are, i.e., we need to order the different security configurations with respect to each security attribute using measures for both security and performance.

However, a key issue with computer security is that it is due to its complex nature hard to measure.

As the title of this thesis indicates, it discusses both security measures and tunable security services. Thus, it can be seen to consist of two parts. In the first part, discussing security measures for tunable security services, an investigation on the security implications of selective encryption by using guesswork as a security measure is made. Built on this an investigation of the relationship between guesswork and entropy. The result shows that guesswork,

after a minor redefinition, is equal to the sum of the entropy and the relative entropy.

The second part contributes to the area of tunable security services, e.g., services that provides several security configurations at run-time. In particular, we present the mobile Crowds (mCrowds) system,

an anonymity technology for the mobile Internet developed at Karlstad University, and a tunable encryption service, that is based on a selective encryption paradigm and designed as a middleware. Finally, an investigation of the tunable features provided by Mix-Nets and Crowds are done, using a conceptual model for tunable security services.

Place, publisher, year, edition, pages
Fakulteten för ekonomi, kommunikation och IT, 2007
Series
Karlstad University Studies, ISSN 1403-8099 ; 2007:39
Keyword
tunable security, security measures, metrics, entropy, guesswork, privacy, anonymity, selective encryption
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-1200 (URN)978-91-7063-142-9 (ISBN)
Presentation
2007-10-23, Sjöströmsalen, 1B 309, Karlstads universitet, Karlstad, 10:00
Opponent
Supervisors
Available from: 2007-10-09 Created: 2007-10-09 Last updated: 2010-09-22
2. Guesswork and Entropy as Security Measures for Selective Encryption
Open this publication in new window or tab >>Guesswork and Entropy as Security Measures for Selective Encryption
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

More and more effort is being spent on security improvements in today's computer environments, with the aim to achieve an appropriate level of security. However, for small computing devices it might be necessary to reduce the computational cost imposed by security in order to gain reasonable performance and/or energy consumption. To accomplish this selective encryption can be used, which provides confidentiality by only encrypting chosen parts of the information. Previous work on selective encryption has chiefly focused on how to reduce the computational cost while still making the information perceptually secure, but not on how computationally secure the selectively encrypted information is. 

Despite the efforts made and due to the harsh nature of computer security, good quantitative assessment methods for computer security are still lacking. Inventing new ways of measuring security are therefore needed in order to better understand, assess, and improve the security of computer environments. Two proposed probabilistic quantitative security measures are entropy and guesswork. Entropy gives the average number of guesses in an optimal binary search attack, and guesswork gives the average number of guesses in an optimal linear search attack. In information theory, a considerable amount of research has been carried out on entropy and on entropy-based metrics. However, the same does not hold for guesswork.

In this thesis, we evaluate the performance improvement when using the proposed generic selective encryption scheme. We also examine the confidentiality strength of selectively encrypted information by using and adopting entropy and guesswork. Moreover, since guesswork has been less theoretical investigated compared to entropy, we extend guesswork in several ways and investigate some of its behaviors.

Place, publisher, year, edition, pages
Karlstad: Karlstad University Press, 2012. 30 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2012:36
Keyword
Computer security, security metrics, selective encryption, confidentiality, entropy, guesswork.
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-14032 (URN)978-91-7063-443-7 (ISBN)
Public defence
2012-09-27, 9C 203, Karlstads universitet, 65187 Karlstad, 13:15 (English)
Opponent
Supervisors
Available from: 2012-09-04 Created: 2012-06-28 Last updated: 2012-09-04Bibliographically approved

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