07381 Executive Summary - Cryptography

The topics covered in the seminar spanned most areas of cryptography, in one way or another, both in terms of the types of schemes (public-key cryptography, symmetric cryptography, hash functions and other cryptographic functions, multi-party protocols, etc.) and in terms of the mathematical methods and techniques used (algebra, number theory, elliptic curves, probability theory, information theory, combinatorics, quantum theory, etc.). The range of applications addressed in the various talks was broad, ranging from secure communication, key management, authentication, digital signatures and payment systems to e-voting and Internet security. While the initial plan had been to focus more exclusively on public-key cryptography, it turned out that this sub-topic branches out into many other areas of cryptography and therefore the organizers decided to expand the scope, emphasizing quality rather than close adherence to public-key cryptography. This decision turned out to be a wise one. What was common to almost all the talks is that rigorous mathematical proofs for the security of the presented schemes were given. In fact, a central topic of many of the talks were proof methodologies for various contexts

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

Quantum cryptography: a practical information security perspective

Quantum Key Exchange (QKE, also known as Quantum Key Distribution or QKD) allows communicating parties to securely establish cryptographic keys. It is a well-established fact that all QKE protocols require that the parties have access to an authentic channel. Without this authenticated link, QKE is vulnerable to man-in-the-middle attacks. Overlooking this fact results in exaggerated claims and/or false expectations about the potential impact of QKE. In this paper we present a systematic comparison of QKE with traditional key establishment protocols in realistic secure communication systems.Comment: 5 pages, new title, published version, minor changes onl