Biblio

HB+ is a lightweight authentication scheme, which is secure against passive attacks if the Learning Parity with Noise Problem (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 distancebounding. 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; moreover, (erroneously) requiring such hardness lowers HB+DB's efficiency and security. We also propose anew distance-bounding protocol called BLOG. It retains parts of HB+DB, yet BLOG is provably secure and enjoys better (asymptotical) security.

Contactless communications have become omnipresent in our daily lives, from simple access cards to electronic passports. Such systems are particularly vulnerable to relay attacks, in which an adversary relays the messages from a prover to a verifier. Distance-bounding protocols were introduced to counter such attacks. Lately, there has been a very active research trend on improving the security of these protocols, but also on ensuring strong privacy properties with respect to active adversaries and malicious verifiers. In particular, a difficult threat to address is the terrorist fraud, in which a far-away prover cooperates with a nearby accomplice to fool a verifier. The usual defence against this attack is to make it impossible for the accomplice to succeed unless the prover provides him with enough information to recover his secret key and impersonate him later on. However, the mere existence of a long-term secret key is problematic with respect to privacy. In this paper, we propose a novel approach in which the prover does not leak his secret key but a reusable session key along with a group signature on it. This allows the adversary to impersonate him even without knowing his signature key. Based on this approach, we give the first distance-bounding protocol, called SPADE, integrating anonymity, revocability and provable resistance to standard threat models.