Certificat électronique | EPFL Graph Search

thumb|right|350px|Certificat électronique client-serveur de comifuro.net Un certificat électronique (aussi appelé certificat numérique ou certificat de clé publique) peut être vu comme une carte d'identité numérique. Il est utilisé principalement pour identifier et authentifier une personne physique ou morale, mais aussi pour chiffrer des échanges. Il est signé par un tiers de confiance qui atteste du lien entre l'identité physique et l'entité numérique (virtuelle). Pour un site web il s'agit d'un certificat SSL. Le standard le plus utilisé pour la création des certificats numériques est le X.509. Rappels sur le chiffrement Le principe de fonctionnement des certificats électroniques est basé sur le chiffrement d'informations et sur la confiance. Pour cela, il existe deux méthodes de chiffrement : symétrique et asymétrique. Chiffrement symétrique Cette méthode est la plus simple à comprendre : si Anne (A) veut envoyer un message chiffré à Bob (B) elle doit lui

High performance VLSI architectures implementing strong cryptographic primitives

Feth Allah Cherigui

The main topic of this thesis is related to the state of the art in designing cryptographic primitives from a hardware point of view. A special emphasis is dedicated to low-power/low-energy CMOS design. A set of solutions is proposed including an LFSR based stream cipher with self-synchronizing capabilities, a new memory-less Rijndael block cipher architecture and a public key scheme in the class of discrete logarithm. The former is based on arithmetic in large finite field, mainly Galois extension field GF(2‴). These solutions are droved using low-energy techniques, in order to decrease both the switching activity and the total delay. The fundamental motivation supporting this work, is to demonstrate that practical solutions can be obtained for implementing such complex primitives in large scaled circuits, that arc at once, high performance architectures (low-power, high-speed) and cryptographicaly strong, using the well known trade-off between area-speed or area-power. Security constraint has been duly considered, mainly by increasing the key-size. In this work, we explore the general aspects of designing the above mentioned cryptographic functions. We give an extensive survey of some cryptographic primitives from the hardware point of view and expose their security properties. The thesis favours stream cipher and public-key schemes, as currently the most promising advance to capture the notion of key generation and establishment and data bulk encryption. One contribution is the convenient notation for expressing cryptographic self-synchronizing stream ciphers SSSC schemes and our SSMG proposal, a scheme based on packet fingerprint identification, that relies on keyed cryptographic hash function to achieve the security requirements. We maintain an important distinction between hardware implementation and algorithm's security, because the security of cryptographic primitives cannot be based on mathematically strong functions only but requires an extensive cryptanalysis at different levels including the application. This causes a concern for a formalization of the security of an implemented cryptographic primitive. Nevertheless, while some schemes arc well known to be secure such as DL based public key schemes and enough cryptanalyzed such as the new standard Rijndael, some security aspects of the SSMG are discussed. A part of this work studies the specific aspects related to hardware implementation of Rijndael block cipher, the new standard designed to be a substitute for DES. An efficient architecture is developed targeting FPGA implementation, by simply avoiding memory blocks dedicated to the implementation of S-boxes and replacing them by on-chip forward computation using composite Galois field. This technique helps to reduce considerably the amount of hardware required at the cost of little increase of the switching activity. The main conclusion is that, while security constraint of cryptographic primitives increases the hardware complexity and reduces the performances, practical solutions exist for reducing such complexities while keeping or increasing the level of security. Nevertheless, major open questions remain both for a firm theoretical foundation and the proper cryptanalysis of certain solutions.

EPFL2002

Location verification and key management in wireless networks

Srdan Capkun

This thesis is primarily concerned with two security mechanisms for wireless networks: location verification and key management. These mechanisms are potential building blocks in the security architectures of a range of applications. Under location verification, we consider mechanisms for secure encounter, distance and position verification. Possible applications of location verification mechanisms include node tracking, secure topology discovery, secure positioning and the detection of node removal and stealing. Key management protocols are used to ensure that correct public keys of entities are known and used with the entities to which they correspond, and that correct shared secret keys are used with the entities with which they are established. Key management protocols thus provide a good basis for achieving various security objectives, such as securing routing, or the protection of users' personal communications. In the first part of this thesis, we propose several location verification mechanisms and we show their applicability to wireless networks. First, we analyze the resistance of the distance and position measurement techniques to attacks. We then propose mechanisms for secure position verification. We further demonstrate the applicability of these mechanisms to secure positioning and node removal detection in wireless multi-hop networks. We then present a set of mechanisms for the verification of node encounters in wireless multi-hop networks. Finally, we show how encounter verification can be used to prevent wormhole attacks, to secure lastencounter routing, and to secure topology discovery. Our location verification mechanisms are based on distance-bounding and distance estimation techniques, and rely on conventional cryptographic primitives. In the second part of the thesis, we propose a straightforward, mobility-assisted technique that can be used 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 which appropriate cryptographic protocols are run. We illustrate the operation of the solution in fully self-organized ad hoc networks, and in ad hoc networks that are controlled by an off-line central authority. We then explore routing in ad hoc networks in which security associations are not established between all pairs of nodes. We show that in that case, secure routing is still possible, and we propose related protocols. We then propose a set of protocols for public-key management in self-organized ad hoc networks. We base our approach on public-key certificates and certificate chaining. We show that this approach is efficient in scenarios in which users issue mutual certificates in a random manner, and in those in which users create PGP-like certificate graphs. We further present a detailed analysis of the PGP certificate graph and we show that this graph exhibits some small world properties. We also present a model for the construction of PGP-like small world certificate graphs.

EPFL2004

ClaimChain: Improving the Security and Privacy of In-band Key Distribution for Messaging

Carmela González Troncoso, Bogdan Kulynych, Wouter Lueks

The social demand for email end-to-end encryption is barely supported by mainstream service providers. Autocrypt is a new community -driven open specification for e-mail encryption that attempts to respond to this demand. In Autocrypt the encryption keys are attached directly to messages, and thus the encryption can be implemented by email clients without any collaboration of the providers. The decentralized nature of this in-band key distribution, however, makes it prone to man-in-the-middle attacks and can leak the social graph of users. To address this problem we introduce ClaimChain, a cryptographic construction for privacy-preserving authentication of public keys. Users store claims about their identities and keys, as well as their beliefs about others, in ClaimChains. These chains form authenticated decentralized repositories that enable users to prove the authenticity of both their keys and the keys of their contacts. ClaimChains are encrypted, and therefore protect the stored information, such as keys and contact identities, from prying eyes. At the same time, ClaimChain implements mechanisms to provide strong non-equivocation properties, discouraging malicious actors from distributing conflicting or inauthentic claims. We implemented ClaimChain and we show that it offers reasonable performance, low overhead, and authenticity guarantees.

ACM2018