Towards Secure Distance Bounding

Relay attacks (and, more generally, man-in-the-middle attacks) are a serious threat against many access control and payment schemes. In this work, we present distance-bounding protocols, how these can deter relay attacks, and the security models formalizing these protocols. We show several pitfalls making existing protocols insecure (or at least, vulnerable, in some cases). Then, we introduce the SKI protocol which enjoys resistance to all popular attack-models and features provable security. As far as we know, this is the first protocol with such all-encompassing security guarantees

On the optimal resistance against mafia and distance fraud in distance-bounding protocols

peer reviewedDistance-bounding protocols are security protocols with a time measurement phase used to detect relay attacks, whose security is typically measured against mafia-fraud and distance-fraud attacks. A prominent subclass of distance-bounding protocols, known as lookup-based protocols, use simple lookup operations to diminish the impact of the computation time in the distance calculation. Independent results have found theoretical lower bounds [Formula presented] and [Formula presented], where n is the number of time measurement rounds, on the security of lookup-based protocols against mafia and distance-fraud attacks, respectively. However, it is still an open question whether there exists a protocol achieving both security bounds. This article closes this question in two ways. First, we prove that the two lower bounds are mutually exclusive, meaning that there does not exist a lookup-based protocol that provides optimal protection against both types of attacks. Second, we provide a lookup-based protocol that approximates those bounds by a small constant factor. Our experiments show that, restricted to a memory size that linearly grows with n, our protocol offers strictly better security than previous lookup-based protocols against both types of fraud

Security of Ubiquitous Computing Systems

The chapters in this open access book arise out of the EU Cost Action project Cryptacus, the objective of which was to improve and adapt existent cryptanalysis methodologies and tools to the ubiquitous computing framework. The cryptanalysis implemented lies along four axes: cryptographic models, cryptanalysis of building blocks, hardware and software security engineering, and security assessment of real-world systems. The authors are top-class researchers in security and cryptography, and the contributions are of value to researchers and practitioners in these domains. This book is open access under a CC BY license

Quantifying pervasive authentication: the case of the Hancke-Kuhn protocol

As mobile devices pervade physical space, the familiar authentication patterns are becoming insufficient: besides entity authentication, many applications require, e.g., location authentication. Many interesting protocols have been proposed and implemented to provide such strengthened forms of authentication, but there are very few proofs that such protocols satisfy the required security properties. The logical formalisms, devised for reasoning about security protocols on standard computer networks, turn out to be difficult to adapt for reasoning about hybrid protocols, used in pervasive and heterogenous networks. We refine the Dolev-Yao-style algebraic method for protocol analysis by a probabilistic model of guessing, needed to analyze protocols that mix weak cryptography with physical properties of nonstandard communication channels. Applying this model, we provide a precise security proof for a proximity authentication protocol, due to Hancke and Kuhn, that uses a subtle form of probabilistic reasoning to achieve its goals.Comment: 31 pages, 2 figures; short version of this paper appeared in the Proceedings of MFPS 201

Secure & Lightweight Distance-Bounding

Distance-bounding is a practical solution to be used in security-sensitive contexts, mainly to prevent relay attacks. The main challenge when designing such protocols is maintaining their inexpensive cryptographic nature, whilst being able to protect against as many, if not all, of the classical threats posed in their context. Moreover, in distance-bounding, some subtle security shortcomings related to the PRF (pseudorandom function) assumption and ingenious attack techniques based on observing verifiers' outputs have recently been put forward. Also, the recent terrorist-fraud by Hancke somehow recalls once more the need to account for noisy communications in the security analysis of distance-bounding. In this paper, we attempt to incorporate the lessons taught by these new developments in our distance-bounding protocol design. The result is a new class of protocols, with increasing levels of security, accommodating the latest advances; at the same time, we preserve the lightweight nature of the design throughout the whole class

Optimal Proximity Proofs

Provably secure distance-bounding is a rising subject, yet an unsettled one; indeed, very few distance-bounding protocols, with formal security proofs, have been proposed. In fact, so far only two protocols, namely SKI (by Boureanu et al.) and FO (by Fischlin and Onete), offer all-encompassing security guaranties, i.e., resistance to distance-fraud, mafia-fraud, and terrorist-fraud. Matters like security, alongside with soundness, or added tolerance to noise do not always coexist in the (new) distance-bounding designs. Moreover, as we will show in this paper, efficiency and simultaneous protection against all frauds seem to be rather conflicting matters, leading to proposed solutions which were/are sub-optimal. In fact, in this recent quest for provable security, efficiency has been left in the shadow. Notably, the tradeoffs between the security and efficiency have not been studied. In this paper, we will address these limitations, setting the "security vs. efficiency" record straight. Concretely, by combining ideas from SKI and FO, we propose symmetric protocols that are efficient, noise-tolerant and-at the same time-provably secure against all known frauds. Indeed, our new distance-bounding solutions outperform the two aforementioned provably secure distance-bounding protocols. For instance, with a noise level of 5%, we obtain the same level of security as those of the pre-existent protocols, but we reduce the number of rounds needed from 181 to 54

Security of Ubiquitous Computing Systems

The chapters in this open access book arise out of the EU Cost Action project Cryptacus, the objective of which was to improve and adapt existent cryptanalysis methodologies and tools to the ubiquitous computing framework. The cryptanalysis implemented lies along four axes: cryptographic models, cryptanalysis of building blocks, hardware and software security engineering, and security assessment of real-world systems. The authors are top-class researchers in security and cryptography, and the contributions are of value to researchers and practitioners in these domains. This book is open access under a CC BY license

Bootstrapping adoption of the Pico password replacement system

In previous work we presented Pico, an authentication sys- tem designed to be both more usable and more secure than passwords. One unsolved problem was that Pico, in its quest to explore the whole solution space without being bound by compatibility shackles, requires changes at both the prover and the verifier, which makes it hard to convince anyone to adopt it: users won’t buy an authentication gadget that doesn’t let them log into anything and service providers won’t sup- port a system that no users are equipped to log in with. In this paper we present three measures to break this vicious circle, starting with the “Pico Lens” browser add-on that rewrites websites on the fly so that they appear Pico-enabled. Our add-on offers the user most (though not all) of the usability and security benefits of Pico, thus fostering adoption from users even before service providers are on board. This will enable Pico to build up a user base. We also developed a server-side Wordpress plugin which can serve both as a reference example and as a useful enabler in its own right (as Wordpress is one of the leading content management platforms on the web). Finally, we developed a software version of the Pico client running on a smartphone, the Pico App, so that people can try out Pico (at the price of slightly reduced security) without having to acquire and carry another gadget. Having broken the vicious circle we’ll be in a stronger position to persuade providers to offer support for Pico in parallel with passwords.ERC 30722

Mechanised Models and Proofs for Distance-Bounding

In relay attacks, a man-in-the-middle adversary impersonates a legitimate party and makes it this party appear to be of an authenticator, when in fact they are not. In order to counteract relay attacks, distance-bounding protocols provide a means for a verifier (e.g., an payment terminal) to estimate his relative distance to a prover (e.g., a bankcard). We propose FlexiDB, a new cryptographic model for distance bounding, parameterised by different types of fine-grained corruptions. FlexiDB allows to consider classical cases but also new, generalised corruption settings. In these settings, we exhibit new attack strategies on existing protocols. Finally, we propose a proof-of-concept mechanisation of FlexiDB in the interactive cryptographic prover EasyCrypt. We use this to exhibit a flavour of man-in-the-middle security on a variant of MasterCard\u27s contactless-payment protocol