Dr David Gerault

Whilst proximity-checking mechanisms are on the rise, proximity-based attacks other than relaying have not been studied from a practical viewpoint, not even in academia. Are the simplest proximity-based attacks, namely distance frauds, a practical danger? Can an attacker make it look like they are here and there at the same time? In this paper, we first distinguish “credible” vs. impractical distance frauds, in a quantifiable, formal manner. Second, we implement two “credible” distance frauds on off-the-shelf NFC-enabled Android phones. We present an initial evaluation focused on their feasibility.

Distance-bounding protocols were introduced in 1993 as a countermeasure to relay attacks, in which an adversary fraudulently forwards the communication between a verifier and a distant prover. In the more than 40 different protocols that followed, assumptions were taken on the structure of distance-bounding protocols and their threat models. In this paper, we survey works disrupting these assumptions, and discuss the remaining challenges.

HB+ is a lightweight authentication scheme, which is secure against passive attacks if the Learning Parity with Noise Prob- lem (LPN) is hard. However, HB+ is vulnerable to a key- recovery, man-in-the-middle (MiM) attack dubbed GRS. The HB+DB protocol added a distance-bounding dimension to HB+, and was experimentally proven to resist the GRS attack. We exhibit several security flaws in HB+DB. First, we refine the GRS strategy to induce a different key-recovery MiM attack, not deterred by HB+DB's distance bounding. Second, we prove HB+DB impractical as a secure distance-bounding (DB) protocol, as its DB security-levels scale poorly compared to other DB protocols. Third, we refute that HB+DB's security against passive attackers relies on the hardness of LPN; more-over, (erroneously) requiring such hardness lowers HB+DB's efficiency and security. We also propose a new distance-bounding protocol called BLOG. It retains parts of HB+DB, yet BLOG is provably secure and enjoys better (asymptotical) security.

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's contactless-payment protocol.

In the current generation of networks, there has been a strong focus on security and integrity. In sixth-generation (6G) networks trust will also be an important requirement, but how do we build trust in a network? Many researchers have started to pay attention to this, but research in this field is still at an early stage. Taking our lead from the development of trusted computing for single devices we require a root of trust and a mechanism for reliably measuring and reporting on the state of the network. In this paper, we survey existing technologies that we feel can be used to achieve this. We explore trusted computing technologies that enable a single device to be trusted and suggest how they can be adapted to help build a trusted network. For reporting, we need a mechanism to immutably store measurements on the system. We consider that distributed ledger technologies could fulfil this role as they offer immutability, decentralised consensus, and transparency.