Shake well before use: Authentication based on Accelerometer Data

Small, mobile devices without user interfaces, such as Bluetooth headsets, often need to communicate securely over wireless networks. Active attacks can only be prevented by authenticating wireless communication, which is problematic when devices do not have any a priori information about each other. We introduce a new method for device-to-device authentication by shaking devices together. This paper describes two protocols for combining cryptographic authentication techniques with known methods of accelerometer data analysis to the effect of generating authenticated, secret keys. The protocols differ in their design, one being more conservative from a security point of view, while the other allows more dynamic interactions. Three experiments are used to optimize and validate our proposed authentication method

Using quantum key distribution for cryptographic purposes: a survey

The appealing feature of quantum key distribution (QKD), from a cryptographic viewpoint, is the ability to prove the information-theoretic security (ITS) of the established keys. As a key establishment primitive, QKD however does not provide a standalone security service in its own: the secret keys established by QKD are in general then used by a subsequent cryptographic applications for which the requirements, the context of use and the security properties can vary. It is therefore important, in the perspective of integrating QKD in security infrastructures, to analyze how QKD can be combined with other cryptographic primitives. The purpose of this survey article, which is mostly centered on European research results, is to contribute to such an analysis. We first review and compare the properties of the existing key establishment techniques, QKD being one of them. We then study more specifically two generic scenarios related to the practical use of QKD in cryptographic infrastructures: 1) using QKD as a key renewal technique for a symmetric cipher over a point-to-point link; 2) using QKD in a network containing many users with the objective of offering any-to-any key establishment service. We discuss the constraints as well as the potential interest of using QKD in these contexts. We finally give an overview of challenges relative to the development of QKD technology that also constitute potential avenues for cryptographic research.Comment: Revised version of the SECOQC White Paper. Published in the special issue on QKD of TCS, Theoretical Computer Science (2014), pp. 62-8

Introducing Accountability to Anonymity Networks

Many anonymous communication (AC) networks rely on routing traffic through proxy nodes to obfuscate the originator of the traffic. Without an accountability mechanism, exit proxy nodes risk sanctions by law enforcement if users commit illegal actions through the AC network. We present BackRef, a generic mechanism for AC networks that provides practical repudiation for the proxy nodes by tracing back the selected outbound traffic to the predecessor node (but not in the forward direction) through a cryptographically verifiable chain. It also provides an option for full (or partial) traceability back to the entry node or even to the corresponding user when all intermediate nodes are cooperating. Moreover, to maintain a good balance between anonymity and accountability, the protocol incorporates whitelist directories at exit proxy nodes. BackRef offers improved deployability over the related work, and introduces a novel concept of pseudonymous signatures that may be of independent interest. We exemplify the utility of BackRef by integrating it into the onion routing (OR) protocol, and examine its deployability by considering several system-level aspects. We also present the security definitions for the BackRef system (namely, anonymity, backward traceability, no forward traceability, and no false accusation) and conduct a formal security analysis of the OR protocol with BackRef using ProVerif, an automated cryptographic protocol verifier, establishing the aforementioned security properties against a strong adversarial model

A three round authenticated group key agreement protocol for ad hoc networks

International audienceGroup Key Agreement (GKA) protocols enable the participants to derive a key based on each one's contribution over a public network without any central authority. They also provide efficient ways to change the key when the participants change. While some of the proposed GKA protocols are too resource consuming for the constraint devices often present in ad hoc networks, others lack a formal security analysis. In this paper, we propose a simple, efficient and secure GKA protocol well-suited to ad hoc networks and present results of our implementation of the same in a prototype application

Efficient key exchange with tight security reduction

In this paper, we propose two authenticated key exchange (AKE) protocols, SMEN and SMEN−, which have efficient online computation and tight security proof in the extended Canetti-Krawczyk (eCK) model. SMEN takes 1.25 exponentiations in online computation, close to that (1.17 exponentiations) of the most efficient AKEs MQV and its variants HMQV and CMQV. SMEN has a security reduction as tight as that of NAXOS, which is the first AKE having a tight security reduction in the eCK model. As a comparison, MQV does not have a security proof; both HMQV and CMQV have a highly non-tight security reduction, and HMQV needs a non-standard assumption; NAXOS takes 2.17 exponentiations in online computation; NETS, a NAXOS variant, takes two online exponentiations in online computation. SMEN simultaneously achieves online efficiency and a tight security proof at a cost of 0.17 more exponentiations in offline computation and the restriction that one party is not allowed to establish a key with itself. SMEN− takes 1.29 exponentiations in online computation, but SMEN− does not use the static private key to compute the ephemeral public key (as does in SMEN, NAXOS, CMQV, and NETS), and hence reduces the risk of leaking the static private key

Towards Post-Quantum Security for Signal's X3DH Handshake

Modern key exchange protocols are usually based on the Diffie–Hellman (DH) primitive. The beauty of this primitive, among other things, is its potential reusage of key shares: DH shares can be either used a single time or in multiple runs. Since DH-based protocols are insecure against quantum adversaries, alternative solutions have to be found when moving to the post-quantum setting. However, most post-quantum candidates, including schemes based on lattices and even supersingular isogeny DH, are not known to be secure under key reuse. In particular, this means that they cannot be necessarily deployed as an immediate DH substitute in protocols. In this paper, we introduce the notion of a split key encapsulation mechanism (split KEM) to translate the desired key-reusability of a DH-based protocol to a KEM-based flow. We provide the relevant security notions of split KEMs and show how the formalism lends itself to lifting Signal’s X3DH handshake to the post-quantum KEM setting without additional message flows. Although the proposed framework conceptually solves the raised issues, instantiating it securely from post-quantum assumptions proved to be non-trivial. We give passively secure instantiations from (R)LWE, yet overcoming the above-mentioned insecurities under key reuse in the presence of active adversaries remains an open problem. Approaching one- sided key reuse, we provide a split KEM instantiation that allows such reuse based on the KEM introduced by Kiltz (PKC 2007), which may serve as a post-quantum blueprint if the underlying hardness assumption (gap hashed Diffie–Hellman) holds for the commutative group action of CSIDH (Asiacrypt 2018). The intention of this paper hence is to raise awareness of the challenges arising when moving to KEM-based key exchange protocols with key-reusability, and to propose split KEMs as a specific target for instantiation in future research