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Guesswork and Entropy as Security Measures for Selective Encryption
Karlstad University, Faculty of Economic Sciences, Communication and IT, Department of Computer Science. (PriSec)
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 [en]
Computer security, security metrics, selective encryption, confidentiality, entropy, guesswork.
National Category
Computer Science
Research subject
Computer Science
Identifiers
URN: urn:nbn:se:kau:diva-14032ISBN: 978-91-7063-443-7 (print)OAI: oai:DiVA.org:kau-14032DiVA: diva2:537964
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
List of papers
1. Middleware Support for Tunable Encryption
Open this publication in new window or tab >>Middleware Support for Tunable Encryption
2006 (English)In: Wireless Information Systems: Proceedings of the 5th International Workshop on Wireless Information Systems / [ed] Qusay H. Mahmoud, Hans Weghorn, Setubal , Portugal: INSTICC Press , 2006, 36-46 p.Conference paper, Oral presentation only (Refereed)
Abstract [en]

To achieve an appropriate tradeoff between security and performance for wireless applications, a tunable and differential treatment of security is required.

In this paper, we present a tunable encryption service designed as a middleware that is based on a selective encryption paradigm. The core component of the middleware provides block-based selective encryption. Although the selection of which data to encrypt is made by the sending application and is typically content-dependent, the representation used by the core component is application and content-independent. This frees the selective decryption module at the receiver from the need for application or content-specific knowledge. The sending application specifies the data to encrypt either directly or through a set of highlevel application interfaces. A prototype implementation of the middleware isdescribed along with an initial performance evaluation. The experimental results demonstrate that the generic middleware service offers a high degree of security adaptiveness at a low cost.

 

Place, publisher, year, edition, pages
Setubal , Portugal: INSTICC Press, 2006
National Category
Computer Systems
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-1919 (URN)978-972-8865-48-1 (ISBN)
Conference
The 5th International Workshop on Wireless Information Systems, WIS 2006, in conjunction with ICEIS 2006, Paphos, Cyprus, May 2006
Available from: 2007-10-09 Created: 2007-10-09 Last updated: 2017-12-06Bibliographically approved
2. Using Guesswork as a Measure for Confidentiality of Selectively Encrypted Messages
Open this publication in new window or tab >>Using Guesswork as a Measure for Confidentiality of Selectively Encrypted Messages
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
Series
Advances in Information Security, ISSN 1568-2633 ; 23-4
National Category
Computer Systems
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-1915 (URN)10.1007/978-0-387-36584-8_14 (DOI)
Available from: 2007-10-09 Created: 2007-10-09 Last updated: 2017-12-06Bibliographically approved
3. On the Relationship between Confidentiality Measures: Entropy and Guesswork
Open this publication in new window or tab >>On the Relationship between Confidentiality Measures: Entropy and Guesswork
2007 (English)In: WOSIS / [ed] Mariemma Inmaculada Yagüe del Valle and Eduardo Fernández-Medina, INSTICC Press , 2007, 135-144 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, we investigate in detail the relationship between entropy and guesswork. The aim of the study is to lay the ground for future efficiency comparison of guessing strategies. After a short discussion of the two measures, and the differences between them, the formal definitions are given. Then, a redefinition of guesswork is made, since the measure is not completely accurate. The change is a minor modification in the last term of the sum expressing guesswork. Finally, two theorems are stated. The first states that the redefined guesswork is equal to the concept of cross entropy, and the second states, as a consequence of the first theorem, that the redefined guesswork is equal to the sum of the entropy and the relative entropy.

Place, publisher, year, edition, pages
INSTICC Press, 2007
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-1916 (URN)978-972-8865-96-2 (ISBN)
Conference
Proceedings of the 5th International Workshop on Security in Information Systems (WOSIS 2007), In conjunction with ICEIS 2007, Funchal, Madeira, Portugal, June 2007
Available from: 2007-10-09 Created: 2007-10-09 Last updated: 2017-12-06Bibliographically approved
4. Joint and Conditional Guesswork: Definitions and Implications
Open this publication in new window or tab >>Joint and Conditional Guesswork: Definitions and Implications
2011 (English)In: Journal of Information Assurance and Security, ISSN 1554-1010, Vol. 6, no 2, 89-97 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Atlanta, GA, USA: Dynamic Publishers Incorporation, 2011
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-10424 (URN)
Available from: 2012-02-08 Created: 2012-02-08 Last updated: 2017-12-06Bibliographically approved
5. Changes in Guesswork over Time in Multi-processor Attacks
Open this publication in new window or tab >>Changes in Guesswork over Time in Multi-processor Attacks
2012 (English)In: Journal of Information Assurance and Security, ISSN 1554-1010, Vol. 7, 145-150 p.Article in journal (Refereed) Published
Abstract [en]

More and more effort is being spent on security improvements in today's computer networking environments. However, due to the nature of computer security there is still a lack of good quantitative assessment methods. Inventing and developing new ways of measuring security are therefore needed in order to more exact describe, assess, and improve security of computer environments. One existing quantitative security measure is guesswork. Guesswork gives the average number of guesses in a brute force attack when breaking an encrypted message. In the current definition of guesswork it is assumed that the attacker uses a single processor when breaking an encrypted message. However, an intelligent and motivated attacker will likely use several processors that can work in parallel to break an encrypted message. This paper formally investigates how guesswork changes over time in multi-processor attacks. The result is applied on three probability distributions, the English alphabet, the geometric, and the truncated geometric to illustrate some behaviors.

Place, publisher, year, edition, pages
Atlanta, GA, USA: Dynamic Publishers Incorporation, 2012
Keyword
computer security, guesswork, multi-processor attacks, quantitative assessment, security measures
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-14094 (URN)10.1109/ISIAS.2011.6122810 (DOI)
Note

Print ISBN 978-1-4577-2154-0

Available from: 2012-06-29 Created: 2012-06-29 Last updated: 2017-12-06Bibliographically approved
6. Security Implications of Selective Encryption
Open this publication in new window or tab >>Security Implications of Selective Encryption
2010 (English)In: MetriSec'10: Proceedings of the 6th International Workshop on Security Measurements and Metrics, New York: ACM , 2010Conference paper, Published paper (Refereed)
Abstract [en]

To be able to perform an analytical and more exact description of security, quantitative security measures are desirable. Two proposed quantitative security measures are entropy and guesswork. When breaking an encrypted message, entropy measures the average number of guesses in an optimal binary search attack, whereas guesswork measures the average number of guesses in an optimal linear search attack. In this paper, we continue to investigate the security implications of a generic selective encryption procedure. That is, how entropy and guesswork changes with the number of encrypted units, i.e., the encryption level. This is done for languages up to thesecond order by deriving equations for entropy of selectively encrypted messages and then transferring the result to guesswork through an equation relating the two measures. Furthermore, unlike entropy, guesswork does not possess the chain rule, however, through the equation relating entropy and guesswork an equation connecting the different guessworks is derived.

Place, publisher, year, edition, pages
New York: ACM, 2010
Keyword
Computer Security, Security Measures, Selective Encryption, Entropy, Guesswork
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-10005 (URN)10.1145/1853919.1853931 (DOI)978-1-4503-0340-8 (ISBN)
Conference
MetriSec'10 The 6th International Workshop on Security Measurements and Metrics(Conference ESEM '10 ACM-IEEE International Symposium on Empirical Software Engineering and Measurement) Bolzano, Italy — September 16 - 17, 2010
Available from: 2012-02-08 Created: 2012-02-08 Last updated: 2017-12-06Bibliographically approved
7. Entropy of Selectively Encrypted Strings
Open this publication in new window or tab >>Entropy of Selectively Encrypted Strings
2011 (English)In: Information Security Theory and Practice: Security and Privacy of Mobile Devices in Wireless Communication / [ed] Claudio A. Ardagna, Jianying Zhou, Springer Berlin/Heidelberg, 2011, 234-243 p.Conference paper, Published paper (Refereed)
Abstract [en]

A feature that has become desirable for low-power mobile devices with limited computing and energy resources is the ability to select a security configuration in order to create a trade-off between security and other important parameters such as performance and energy consumption. Selective encryption can be used to create this trade-off by only encrypting chosen units of the information. In this paper, we continue the investigation of the confidentiality implications of selective encryption by applying entropy on a generic selective encryption scheme. By using the concept of run-length vector from run-length encoding theory, an expression is derived for entropy of selectively encrypted strings when the number of encrypted substrings, containing one symbol, and the order of the language change

Place, publisher, year, edition, pages
Springer Berlin/Heidelberg, 2011
Series
Lecture Notes in Computer Science, ISSN 0302-9743 ; 6633
Keyword
computer security, security measures, selective encryption, entropy
National Category
Computer Science
Research subject
Computer Science
Identifiers
urn:nbn:se:kau:diva-10425 (URN)000306225000016 ()978-3-642-21040-2 (ISBN)
Conference
WISTP11 - 5th IFIP WG 11.2 International Workshop in Information Security Theory and Practice, Heraklion, Crete, Greece, June 1-3, 2011
Available from: 2012-02-08 Created: 2012-02-08 Last updated: 2017-12-06Bibliographically approved

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