Location verification and key management in wireless networks

Srdan Capkun
EPFL, 2004
Thèse EPFL

Résumé

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.

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https://infoscience.epfl.ch/record/33535?ln=fr

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Srdan Capkun
EPFL, 2004
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/33535?ln=fr

À propos de ce résultat

Concepts associés (13)

Concepts associés

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Publications associées (19)

Publications associées

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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

Chargement

Chaum's Designated Confirmer Signature Revisited

Jean Monnerat, Serge Vaudenay

This article revisits the original designated confirmer signature scheme of Chaum. Following the same spirit we naturally extend the Chaum's construction in a more general setting and analyze its security in a formal way. We prove its security in the random oracle model by using a random hash function and a random permutation. We notably consider the confirmer as an attacker against the existential forgery under an adaptive chosen-message attack. This security property is shown to rely on the hardness of forging signatures in a universal way of a classical existentially forgeable signature scheme. Furthermore, we show that the invisibility of the signatures under a non-adaptive chosen-message (aka lunchtime) attack relies on some invisibility properties of an existentially forgeable undeniable signature scheme. The existence of this cryptographic primitive is shown equivalent to the existence of public-key cryptosystems. It is also interesting to see that this article confirms the security of Chaum's scheme since our construction is a natural generalization of this scheme.

2005

Chargement

Our main motivation is to design more user-friendly security protocols. Indeed, if the use of the protocol is tedious, most users will not behave correctly and, consequently, security issues occur. An example is the actual behavior of a user in front of an SSH certificate validation: while this task is of utmost importance, about 99% of SSH users accept the received certificate without checking it. Designing more user-friendly protocols may be difficult since the security should not decrease at the same time. Interestingly, insecure channels coexist with channels ensuring authentication. In practice, these latters may be used for a string comparison or a string copy, e.g., by voice over IP spelling. The shorter the authenticated string is, the less human interaction the protocol requires, and the more user-friendly the protocol is. This leads to the notion of SAS-based cryptography, where SAS stands for Short Authenticated String. In the first part of this thesis, we analyze and propose optimal SAS-based message authentication protocols. By using these protocols, we show how to construct optimal SAS-based authenticated key agreements. Such a protocol enables any group of users to agree on a shared secret key. SAS-based cryptography requires no pre-shared key, no trusted third party, and no public-key infrastructure. However, it requires the user to exchange a short SAS, e.g., five decimal digits. By using the just agreed secret key, the group can now achieve a secure communication based on symmetric cryptography. SAS-based authentication protocols are often used to authenticate the protocol messages of a key agreement. Hence, each new secure communication requires the interaction of the users to agree on the SAS. A solution to reduce the user interaction is to use digital signature schemes. Indeed, in a setup phase, the users can use a SAS-based authentication protocol to exchange long-term verification keys. Then, using digital signatures, users are able to run several key agreements and the authentication of protocol messages is done by digital signatures. In the case where no authenticated channel is available, but a public-key infrastructure is in place, the SAS-based setup phase is avoided since verification keys are already authenticated by the infrastructure. In the second part of this thesis, we also study two problems related to digital signatures: (1) the insecurity of digital signature schemes which use weak hash functions and (2) the privacy issues from signed documents. Digital signatures are often proven to be secure in the random oracle model. The role of random oracles is to model ideal hash functions. However, real hash functions deviate more and more from this idealization. Indeed, weaknesses on hash functions have already been discovered and we are expecting new ones. A question is how to fix the existing signature constructions based on these weak hash functions. In this thesis, we first try to find a better way to model weak hash function. Then, we propose a (randomized) pre-processing to the input message which transforms any weak signature implementation into a strong signature scheme. There remains one drawback due to the randomization. Indeed, the random coins must be sent and thus the signature enlarges. We also propose a method to avoid the increase in signature length by reusing signing coins. Digital signatures may also lead to privacy issues. Indeed, given a message and its signature, anyone can publish the pair which will confirm the authenticity of the message. In certain applications, like in electronic passports (e-passports), publishing the authenticated data leads to serious privacy issues. In this thesis, we define the required security properties in order to protect the data privacy, especially in the case of e-passport verification. The main idea consists for the e-passport to keep the signature secret. The e-passport should only prove that it knows a valid signature instead of revealing it. We propose a new primitive, called Offline Non-Transferable Authentication Protocol (ONTAP), as well as efficient implementations that are compatible with the e-passport standard signature schemes.

EPFL2009

Chargement

EPFL2009

High performance VLSI architectures implementing strong cryptographic primitives

Feth Allah Cherigui

EPFL2002