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Christos Dimitrakakis

Cette personne a quitté l’EPFL

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Publications associées (21)

Page 1 sur 2

Expected Loss Analysis for Authentication in Constrained Channels

Serge Vaudenay, Christos Dimitrakakis, Aikaterini Mitrokotsa

We derive bounds on the expected loss for authentication protocols in channels which are constrained due to noisy conditions and communication costs. This is motivated by a number of authentication protocols, where at least some part of the authentication ...

IOS Press2015

Probabilistic inverse reinforcement learning in unknown environments

Christos Dimitrakakis

We consider the problem of learning by demonstration from agents acting in unknown stochastic Markov environments or games. Our aim is to estimate agent preferences in order to construct improved policies for the same task that the agents are trying to sol ...

2013

Intrusion Detection in MANET Using Classification Algorithms: The Effects of Cost and Model Selection

Christos Dimitrakakis, Aikaterini Mitrokotsa

Intrusion detection is frequently used as a second line of defense in Mobile Ad-hoc Networks (MANETs). In this paper we examine how to properly use classification methods in intrusion detection for MANETs. In order to do so we evaluate five supervised clas ...

Elsevier2013

Linear Bayesian Reinforcement Learning

Christos Dimitrakakis, Nikolaos Tziortziotis

This paper proposes a simple linear Bayesian approach to reinforcement learning. We show that with an appropriate basis, a Bayesian linear Gaussian model is sufficient for accurately estimating the system dynamics, and in particular when we allow for corre ...

2013

Ensembles for sequence learning

Christos Dimitrakakis

This thesis explores the application of ensemble methods to sequential learning tasks. The focus is on the development and the critical examination of new methods or novel applications of existing methods, with emphasis on supervised and reinforcement lear ...

EPFL2007

On Selecting the Nonce Length in Distance-Bounding Protocols

Serge Vaudenay, Christos Dimitrakakis, Aikaterini Mitrokotsa

Distance-bounding protocols form a family of challenge-response authentication protocols that have been introduced to thwart relay attacks. They enable a verifier to authenticate and to establish an upper bound on the physical distance to an untrusted prov ...

Oxford University Press2013

Complexity of stochastic branch and bound methods for belief tree search in Bayesian reinforcement learning

Christos Dimitrakakis

There has been a lot of recent work on Bayesian methods for reinforcement learning exhibiting near-optimal online performance. The main obstacle facing such methods is that in most problems of interest, the optimal solution involves planning in an infinite ...

2009

DUCT: An Upper Confidence Bound Approach to Distributed Constraint Optimization Problems

Boi Faltings, Christos Dimitrakakis, Brammert Ottens

We propose a distributed upper confidence bound approach, DUCT, for solving distributed constraint optimization problems. We compare four variants of this approach with a baseline random sampling algorithm, as well as other complete and incomplete algorith ...

Assoc Computing Machinery2017

Reid et al.'s distance bounding protocol and mafia fraud attacks over noisy channels

Christos Dimitrakakis

Distance bounding protocols are an effective countermeasure against relay attacks including distance fraud, mafia fraud and terrorist fraud attacks. Reid et al. proposed the first symmetric key distance bounding protocol against mafia and terrorist fraud a ...

2010

Online Policy Adaptation for Ensemble Classifiers

Samy Bengio, Christos Dimitrakakis

Ensemble algorithms can improve the performance of a given learning algorithm through the combination of multiple base classifiers into an ensemble. In this paper we attempt to train and combine the base classifiers using an adaptive policy. This policy is ...

2005

Network Self-Organization Explains the Statistics and Dynamics of Synaptic Connection Strengths in Cortex

Christos Dimitrakakis

The information processing abilities of neural circuits arise from their synaptic connection patterns. Understanding the laws governing these connectivity patterns is essential for understanding brain function. The overall distribution of synaptic strength ...

Public Library Science2013

Statistical Decision Making for Authentication and Intrusion Detection

Christos Dimitrakakis, Aikaterini Mitrokotsa

User authentication and intrusion detection differ from standard classification problems in that while we have data generated from legitimate users, impostor or intrusion data is scarce or non-existent. We review existing techniques for dealing with this p ...

2009

Personalized News Recommendation with Context Trees

Boi Faltings, Christos Dimitrakakis, Florent Frédéric Garcin

The proliferation of online news creates a need for filtering interesting articles. Compared to other products, however, recommending news has specific challenges: news preferences are subject to trends, users do not want to see multiple articles with simi ...

2013

Network Self-organization explains the distribution of synaptic efficacies in neocortex

Christos Dimitrakakis

The distribution of synaptic efficacies in neocortex has an approximately lognormal shape. Many weak synaptic connections coexist with few very strong connections such that only 20% of synapses contribute 50% of total synaptic strength. Furthermore, recent ...

2011

Complexity of stochastic branch and bound methods for belief tree search in Bayesian reinforcement learning

Christos Dimitrakakis

2009

DUCT: An upper confidence bound approach to distributed constraint optimization problems

Boi Faltings, Christos Dimitrakakis, Brammert Ottens

The Upper Confidence Bounds (UCB) algorithm is a well-known near-optimal strategy for the stochastic multi-armed bandit problem. Its extensions to trees, such as the Upper Confidence Tree (UCT) algorithm, have resulted in good solutions to the problem of G ...

2012

Expected loss bounds for authentication in constrained channels

Serge Vaudenay, Christos Dimitrakakis, Aikaterini Mitrokotsa

We derive bounds on the expected loss for authenti-cation protocols in channels which are constrained due to noisyconditions and communication costs. This is motivated by anumber of authentication protocols, where at least some partof the authentication is ...

Ieee2012

Bayesian multitask inverse reinforcement learning

Christos Dimitrakakis

We generalise the problem of inverse reinforcement learning to multiple tasks, from multiple demonstrations. Each one may represent one expert trying to solve a different task, or as different experts trying to solve the same task. Our main contribution is ...

2011

Efficient methods for near-optimal sequential decision making under uncertainty

Christos Dimitrakakis

This chapter discusses decision making under uncertainty. More specifically, it offers an overview of efficient Bayesian and distribution-free algorithms for making near-optimal sequential decisions under uncertainty about the environment. Due to the uncer ...

2010

Context models on sequences of covers

Christos Dimitrakakis

We present a class of models that, via a simple construction, enables exact, incremental, non-parametric, polynomial-time, Bayesian inference of conditional measures. The approach relies upon creating a sequence of covers on the conditioning variable and m ...

2011