Publications by Levente Buttyan

Chat with Graph Search

Ask any question about EPFL courses, lectures, exercises, research, news, etc. or try the example questions below.

DISCLAIMER: The Graph Chatbot is not programmed to provide explicit or categorical answers to your questions. Rather, it transforms your questions into API requests that are distributed across the various IT services officially administered by EPFL. Its purpose is solely to collect and recommend relevant references to content that you can explore to help you answer your questions.

Streaming multimedia data on the Internet is developing as a mainstream technology, which attracts many users by providing a new and convenient form of access to online multimedia information. While its strong business potential is obvious, many problems related to charging, copyright protection, and privacy can delay or even hinder its extensive deployment. In this paper, we are concerned with the charging problem, and propose an electronic payment scheme to use for purchasing broadcast multimedia streams.

We propose a new approach to securing computer networks. With this approach, we achieve security in a fully self-organized manner; by this we mean that to secure a computer network, a security system does not require any kind of certification authority or centralized server, even for the initialization phase. In our work, we were inspired by PGP because its functionality relies solely on the acquaintances between users. We show that the small-world phenomenon naturally emerges in the PGP system as a consequ

In contrast with conventional networks, mobile ad hoc networks usually do not provide on-line access to trusted authorities or to centralized servers and they exhibit frequent partitioning due to link and node failures and to node mobility. For these reasons, traditional security solutions that require on-line trusted authorities or certificate repositories are not well suited for securing ad hoc networks. In this paper, we propose a fully self-organized public-key management system that allows users to gen

A fair exchange protocol is a protocol, in which two (or more) mutually suspicious parties exchange their digital items in a way that neither party can gain an advantage over the other by misbehaving. Many fair exchange protocols have been proposed in the academic literature, but they provide rather different types of fairness. The formal comparison of these proposals remained difficult, mainly, because of the lack of a common formal framework, in which each can be modelled and formal fairness definitions c

We introduce a model that allows of anonymous yet accountable service usage in mobile communication systems. This model is based on the introduction of a new business role, called the customer care agency, and a ticket based mechanism for service access. We motivate the introduction of customer care agencies by analyzing their role and emphasizing their advantages. We introduce the general idea of ticket based service access, present a categorization of ticket types and ticket acquisition models, and identi

In multi-hop wireless networks, every node is expected to forward packets for the benefit of other nodes. Yet, if each node is its own authority, then it may selfishly deny packet forwarding in order to save its own resources. Some researchers have proposed to introduce an incentive mechanism in the network that motivates the nodes to cooperate. In this paper, we address the question of whether such an incentive mechanism is necessary or cooperation between the nodes exists in the absence of it. We define a

Method for performing electronic payments between a mobile equipment and a payment terminal over a short distance wireless interface, comprising displaying an identification (for example T; T-id) on the display (110) of said payment terminal (11), manually entering said identification on the input means (103) of said mobile equipment, using said identification in an message to the payment terminal, said message used to start establishment of an extended mutual authentication, said extended mutual authentica

The concept of middleware based architectures for telecommunication services in the broadband, multimedia, and information era is emerging. One representative example is the Telecommunications Information Networking Architecture (TINA), which is characterised by a variety of services, a multitude of service providers, a well defined business model, a middleware platform for service development and provision, and the assumption of advanced costumer premises equipment. Concepts for its security architecture a

In this paper, we provide a formal analysis of a rational exchange protocol proposed by Syverson. A rational exchange protocol guarantees that misbehavior cannot generate benefits, and is therefore discouraged. The analysis is performed using our formal model, which is based on game theory. In this model, rational exchange is defined in terms of a Nash equilibrium.

A fair exchange protocol is a protocol, in which two (or more) mutually suspicious parties exchange their digital items in a way that neither party can gain an advantage over the other by misbehaving. Many fair exchange protocols have been proposed in the academic literature, but they provide rather different types of fairness. The formal comparison of these proposals remained diffcult, mainly, because of the lack of a common formal framework, in which each can be modelled and formal fairness defnitions can

We introduce game theory as a formal framework in which exchange protocols can be modeled and their properties can be studied. We use this framework to give a formal definition for rational exchange relating it to the concept of Nash equilibrium in games. In addition, we study the relationship between rational exchange and fair exchange. We prove that fair exchange implies rational exchange, but the reverse is not true. The practical consequence of this is that rational exchange protocols may provide intere

This paper is a state of the art review of the use of formal methods in the design of cryptographic protocols.

The Terminodes project is designing a wide area, mobile ad-hoc network, which is meant to be used in a public environment, in our approach, the network is run by users themselves. We give a global description of the building blocks used by the basic operation of the network, they all rely on various concepts of self-organization. Routing uses a combination of geography-based information and local, MANET-like protocols. Terminode positioning is obtained either by GPS, or by a relative positioning method. Mob

We propose a straightforward technique to provide peer-to-peer security in mobile networks. We show that far from being a hurdle, mobility can be exploited to set up security associations among users. We leverage on the temporary vicinity of users, during ...

Contrary to the common belief that mobility makes security more difficult to achieve, we show that node mobility can, in fact, be useful to provide security in ad hoc networks. We propose a technique in which security associations between nodes are established, when they are in the vicinity of each other, by exchanging appropriate cryptographic material. We show that this technique is generic, by explaining its application to fully self-organized ad hoc networks and to ad hoc networks placed under an (off-l

We introduce a model that allows anonymous yet accountable access to services in mobile communication systems. This model is based on the introduction of a new business role, called the customer care agency, and a ticket based mechanism for service access. We introduce the general idea of ticket based service access, and present a categorisation of ticket types and ticket acquisition models. We analyse the role of customer care agencies and emphasise their advantages.

In this paper, we address the problem of service availability in mobile ad-hoc WANs. We present a secure mechanism to stimulate end users to keep their devices turned on, to refrain from overloading the network, and to thwart tampering aimed at converting the device into a selfish one. Our solution is based on the application of a tamper resistant security module in each device and cryptographic protection of messages.

We present three attacks against the authentication protocol that has been proposed for the so called global mobility network in \cite{kn:Suz97}. We show that the attacks are feasible and propose corrections that make the protocol more robust and resistant against the presented attacks. Our aim is to highlight some basic design principles for cryptographic protocols, the adherence to which would have prevented these attacks.

Levente Buttyan

Chat with Graph Search

A Payment Scheme for Broadcast Multimedia Streams

Small Worlds in Security Systems: an Analysis of the PGP Certificate Graph

Self-organized public-key management for mobile ad hoc networks

Toward a Formal Model of Fair Exchange - a Game Theoretic Approach

Accountable Anonymous Service Usage in Mobile Communication Systems

Equilibrium Analysis of Packet Forwarding Strategies in Wireless Ad Hoc Networks - the Static Case (extended version)

Method for securing communications between a terminal and an additional user equipment

Multilateral Security in Middleware Based Telecommunications Architectures

A Formal Analysis of Syverson`s Rational Exchange Protocol

Equilibrium Analysis of Packet Forwarding Strategies in Wireless Ad Hoc Networks - the Static Case

Toward a Formal Model of Fair Exchange, a Game Theoretic Approach

Rational Exchange -- A Formal Model Based on Game Theory

Formal methods in the design of cryptographic protocols (state of the art)

Self-Organization in Mobile Ad-Hoc Networks: the Approach of Terminodes

Mobility Helps Peer-to-Peer Security

Mobility Helps Security in Ad Hoc Networks

Accountable Anonymous Access to Services in Mobile Communication Systems

Enforcing Service Availability in Mobile Ad-Hoc WANs

Enforcing Service Availability in Mobile Ad-Hoc WANs

Extensions to an Authentication Technique Proposed for the Global Mobility Network