Axiomatizations of quasi-polynomial functions on bounded chains

in Aequationes Mathematicae (2009), 78(1-2), 195-213

Two emergent properties in aggregation theory are investigated, namely horizontal maxitivity and comonotonic maxitivity (as well as their dual counterparts) which are commonly defined by means of certain ... [more ▼]

Two emergent properties in aggregation theory are investigated, namely horizontal maxitivity and comonotonic maxitivity (as well as their dual counterparts) which are commonly defined by means of certain functional equations. We completely describe the function classes axiomatized by each of these properties, up to weak versions of monotonicity in the cases of horizontal maxitivity and minitivity. While studying the classes axiomatized by combinations of these properties, we introduce the concept of quasi-polynomial function which appears as a natural extension of the well-established notion of polynomial function. We give further axiomatizations for this class both in terms of functional equations and natural relaxations of homogeneity and median decomposability. As noteworthy particular cases, we investigate those subclasses of quasi-term functions and quasi-weighted maximum and minimum functions, and provide characterizations accordingly. [less ▲]

Interdisciplinary cooperation on media effects

Presentation (2009, October)

Writing across the curriculum vs. writing in the disciplines – Gegensatz, Ergänzung oder zwei Seiten einer Medaille?

Scientific Conference (2009, October)

Berezin-Toeplitz quantization of moduli spaces

Scientific Conference (2009, October)

Musikerziehung als Instrument ideologischer Indoktrinierung in der DDR

Scientific Conference (2009, September 30)

On the physical security of cryptographic implementations

Doctoral thesis (2009)

In modern cryptography, an encryption system is usually studied in the so-called black-box model. In this model, the cryptosystem is seen as an oracle replying to message encryption (and/or decryption ... [more ▼]

In modern cryptography, an encryption system is usually studied in the so-called black-box model. In this model, the cryptosystem is seen as an oracle replying to message encryption (and/or decryption) queries according to a secret value: the key. The security of the cryptosystem is then defined following a simple game. An adversary questions the oracle about the encryption (and/or decryption) of messages of its choice and, depending on the answers, attempts to recover the value of the secret key (or to encrypt/decrypt a message for which he did not query the oracle). If by following an optimal strategy the adversary only has a negligible chance of winning, the system is considered as secure. Several cryptosystems have been proved secure in the black-box model. However, this model is not always sufficient to ensure the security of a cryptosystem in practice. Let us consider the example of smart cards which are used as platforms for cryptosystems in various applications such as banking, access control, mobile telephony, pay TV, or electronic passport. By the very nature of these applications, a cryptosystem embedded on a smart card is physically accessible to potential attackers. This physical access invalidates the modeling of the cryptosystem as a simple encryption oracle since it allows the adversary to observe and disrupt its physical behavior. New attacks then become possible which are known as physical cryptanalysis. Physical cryptanalysis includes two main families of attacks: side channel attacks and fault attacks. The purpose of side channel attacks is to analyze the different physical leakages of a cryptographic implementation during its computation. Chief among these rank timing, power consumption, and electromagnetic radiation. Observing these so-called side channels provides sensitive information about the cryptographic computation. The secret key value can then be easily recovered by statistical treatment although the cryptosystem is secure in the black-box model. The access to a cryptographic implementation enables more than a simple observation of its physical behavior; it is also possible to disrupt its computation. Working on this assumption, fault attacks consist in corrupting cryptographic computations so that they produce erroneous results. Surprisingly, these results can be used in order to recover information about the secret key. This thesis focuses on physical cryptanalysis as well as on the secure implementation of cryptographic primitives. We examine in the first part side channel attacks from a theoretical viewpoint. Various techniques of attack based on different statistical tools are addressed. We analyze their success rate, we compare their efficiency and we propose some improvements. Our analyses are illustrated by results of simulated attacks as well as practical attacks on smart cards. The second part of this thesis is devoted to one of the most widely used countermeasures to side channel attacks: data masking. Our investigations concentrate on generic masking schemes for block ciphers such as the encryption standards DES and AES. We analyze existing schemes, exhibiting some attacks against certain of them and we propose new designs. The third and last part of this thesis deals with fault attacks. First, we describe a new attack on the DES cipher which exhibits some requirements to its secure implementation. We then provide a case study based on the RSA cryptosystem where we propose a new countermeasure which can also be applied to secure any exponentiation algorithm. We finally address an important issue for practical security: the implementation of coherence checks. [less ▲]

Gegenwart und Perspektiven der Geographie in Deutschland

Conference given outside the academic context (2009)

Do overweight students experience more physical aggression?

Poster (2009, September)

Findings demonstrated that overweight adolescents are more likely to be both victims and perpetrators of violent acts (Janssen et al., 2004). The present study tested this weight-based victimization ... [more ▼]

Findings demonstrated that overweight adolescents are more likely to be both victims and perpetrators of violent acts (Janssen et al., 2004). The present study tested this weight-based victimization/perpetrator hypothesis. The study sample comprised N1⁄4649 middle school students, which were regrouped in three weight categories (i.e. underweight, normal weight, overweight) according to the cut-offs proposed by the International Obesity Taskforce. In order to analyze group differences between the weight categories, three same sized groups (N 1⁄4 75) were randomly created from the whole data set. Results confirmed that overweight students are more likely to be victimized but not to become perpetrators themselves compared to their peers. Logistic regressions showed that being anxious (OR 1⁄4 2.34), having low self- esteem (OR1⁄40.58), having a higher BMI (OR1⁄41.11) and being male (OR1⁄40.26) are risk factors of victimization. Results will be discussed with respect to psychosocial interventions. [less ▲]

Is the cerebral processing of categorical and coordinate spatial relations based on different or identical but differentially activated functional networks?

Scientific Conference (2009, September)

The fundamental hypothesis related to the distinction between categorical and coordinate processing has been that these two types of spatial relations coding are qualitatively different. Based on ... [more ▼]

The fundamental hypothesis related to the distinction between categorical and coordinate processing has been that these two types of spatial relations coding are qualitatively different. Based on Kosslyn’s initial hemispheric specialization theory, they also are hypothesized to rely on different functional networks in the brain which are supposed to have evolved in a way to take advantage of more fundamental hemispheric specializations in order to adapt these hemispheric strengths to the processing of the two different types of spatial relations. (...) [less ▲]

Postcolonial ideologies of language in education: Teachers and parents on English and local language(s) in The Gambia

in Cuvelier, Pol; Vandekerckhove, Reinhild; Aerts, Ann (Eds.) Multilingualism from Below: Proceedings MIDP Colloquium (2009, September)