Continuous-variable quantum key distribution in fast fading channels

We investigate the performance of several continuous-variable quantum key distribution protocols in the presence of fading channels. These are lossy channels whose transmissivity changes according to a probability distribution. This is typical in communication scenarios where remote parties are connected by free-space links subject to atmospheric turbulence. In this work, we assume the worst-case scenario where an eavesdropper has full control of a fast fading process, so that she chooses the instantaneous transmissivity of a channel, while the remote parties can only detect the mean statistical process. In our study, we consider coherent-state protocols run in various configurations, including the one-way switching protocol in reverse reconciliation, the measurement-device-independent protocol in the symmetric configuration and a three-party measurement-device-independent network. We show that, regardless of the advantage given to the eavesdropper (full control of fading), these protocols can still achieve high rates

Secure Anonymous Conferencing in Quantum Networks

Users of quantum networks can securely communicate via so-called (quantum) conference key agreement—making their identities publicly known. In certain circumstances, however, communicating users demand anonymity. Here, we introduce a security framework for anonymous conference key agreement with different levels of anonymity, which is inspired by the ε-security of quantum key distribution. We present efficient and noise-tolerant protocols exploiting multipartite Greenberger-Horne-Zeilinger (GHZ) states and prove their security in the finite-key regime. We analyze the performance of our protocols in noisy and lossy quantum networks and compare with protocols that only use bipartite entanglement to achieve the same functionalities. Our simulations show that GHZ-based protocols can outperform protocols based on bipartite entanglement and that the advantage increases for protocols with stronger anonymity requirements. Our results strongly advocate the use of multipartite entanglement for cryptographic tasks involving several users

Secure Anonymous Conferencing in Quantum Networks

Users of quantum networks can securely communicate via so-called (quantum) conference key agreement—making their identities publicly known. In certain circumstances, however, communicating users demand anonymity. Here, we introduce a security framework for anonymous conference key agreement with different levels of anonymity, which is inspired by the ε-security of quantum key distribution. We present efficient and noise-tolerant protocols exploiting multipartite Greenberger-Horne-Zeilinger (GHZ) states and prove their security in the finite-key regime. We analyze the performance of our protocols in noisy and lossy quantum networks and compare with protocols that only use bipartite entanglement to achieve the same functionalities. Our simulations show that GHZ-based protocols can outperform protocols based on bipartite entanglement and that the advantage increases for protocols with stronger anonymity requirements. Our results strongly advocate the use of multipartite entanglement for cryptographic tasks involving several users

Lightweight Information Security Methods for Indoor Wireless Body Area Networks: from Channel Modeling to Secret Key Extraction

A group of wirelessly communicating sensors that are placed inside, on or around a human body constitute a Wireless Body Area Network (WBAN). Continuous monitoring of vital signs through WBANs have a potential to revolutionize current health care services by reducing the cost, improving accessibility, and facilitating medical diagnosis. However, sensitive nature of personal health data requires WBANs to integrate appropriate security methods and practices. As limited hardware resources make conventional security measures inadequate in a WBAN context, this work is focused on alternative techniques based on Wireless Physical Layer Security (WPLS). More specifically, we introduce a symbiosis of WPLS and Compressed Sensing to achieve security at the time of sampling. We successfully show how the proposed framework can be applied to electrocardiography data saving significant computational and memory resources. In the scenario when a WBAN Access Point can make use of diversity methods in the form of Switch-and-Stay Combining, we demonstrate that output Signal-to-Noise Ratio (SNR) and WPLS key extraction rate are optimized at different switching thresholds. Thus, the highest key rate may result in significant loss of output SNR. In addition, we also show that the past WBAN off-body channel models are insufficient when the user exhibits dynamic behavior. We propose a novel Rician based off-body channel model that can naturally reflect body motion by randomizing Rician factor K and considering small and large scale fading to be related. Another part of our investigation provides implications of user\u27s dynamic behavior on shared secret generation. In particular, we reveal that body shadowing causes negative correlation of the channel exposing legitimate participants to a security threat. This threat is analyzed from a qualitative and quantitative perspective of a practical secret key extraction algorithm

Semi-Quantum Conference Key Agreement (SQCKA)

A need in the development of secure quantum communications is the scalable extension of key distribution protocols. The greatest advantage of these protocols is the fact that its security does not rely on mathematical assumptions and can achieve perfect secrecy. In order to make these protocols scalable, has been developed the concept of Conference Key Agreements, among multiple users. In this thesis we propose a key distribution protocol among several users using a semi-quantum approach. We assume that only one of the users is equipped with quantum devices and generates quantum states, while the other users are classical, i.e., they are only equipped with a device capable of measuring or reflecting the information. This approach has the advantage of simplicity and reduced costs. We prove our proposal is secure and we present some numerical results on the lower bounds for the key rate. The security proof applies new techniques derived from some already well established work. From the practical point of view, we developed a toolkit called Qis|krypt⟩ that is able to simulate not only our protocol but also some well-known quantum key distribution protocols. The source-code is available on the following link: - https://github.com/qiskrypt/qiskrypt/.Uma das necessidades no desenvolvimento de comunicações quânticas seguras é a extensão escalável de protocolos de distribuição de chaves. A grande vantagem destes protocolos é o facto da sua segurança não depender de suposições matemáticas e poder atingir segurança perfeita. Para tornar estes protocolos escaláveis, desenvolveu-se o conceito de Acordo de Chaves de Conferência, entre múltiplos utilizadores. Nesta tese propomos um protocolo para distribuição de chaves entre vários utilizadores usando uma abordagem semi-quântica. Assumimos que apenas um dos utilizadores está equipado com dispositivos quânticos e é capaz de gerar estados quânticos, enquanto que os outros utilizadores são clássicos, isto é, estão apenas equipados com dispositivos capazes de efectuar uma medição ou refletir a informação. Esta abordagem tem a vantagem de ser mais simples e de reduzir custos. Provamos que a nossa proposta é segura e apresentamos alguns resultados numéricos sobre limites inferiores para o rácio de geração de chaves. A prova de segurança aplica novas técnicas derivadas de alguns resultados já bem estabelecidos. Do ponto de vista prático, desenvolvemos uma ferramenta chamada Qis|krypt⟩ que é capaz de simular não só o nosso protocolo como também outros protocolos distribuição de chaves bem conhecidos. O código fonte encontra-se disponível no seguinte link: - https://github.com/qiskrypt/qiskrypt/

Sichere Kommunikation über Abhörkanäle mit mehreren Empfängern und aktiven Störsendern

We derive a state of the art strong secrecy coding scheme for the multi-receiver wiretap channel under the joint and individual secrecy constraints. we show that individual secrecy can utilize the concept of mutual trust to achieve a larger capacity region compared to the joint one. Further, we derive a full characterization for the list secrecy capacity of arbitrarily varying wiretap channels and establish some interesting results for the continuity and additivity behaviour of the capacity.Für den Abhörkanal mit mehreren Empfängern wird ein Kodierungsschema hergeleitet unter dem gemeinsamen als auch individuellem Sicherheitskriterium. Das individuelle Kriterium basiert auf dem Konzept des gegenseitigen Vertrauens, um eine größere Kapazitätsregion zu erreichen. Weiterhin wird eine vollständige Charakterisierung der Sicherheitskapazität für den beliebig variierenden Kanals aufgestellt, sowie Eigenschaften bezüglich der Kontinuität und des Additivitätsverhalten bewiesen

MULTI-PHOTON TOLERANT QUANTUM KEY DISTRIBUTION PROTOCOLS FOR SECURED GLOBAL COMMUNICATION

This dissertation investigates the potential of multi-photon tolerant protocols for satellite-aided global quantum key distribution (QKD). Recent investigations like braided single-stage protocol and the implementation of the three-stage protocol in fiber have indicated that multi-photon tolerant protocols have wide-ranging capabilities for increasing the distance and speed of quantum-secure communication. This dissertation proposes satellite-based network multicasting and its operation that can profitably use multi-photon tolerant protocols for quantum-secure global communication. With a growingly interconnected world and an increasing need for security in communication, communication satellites at Lower Earth Orbits (LEO), Medium Earth Orbit (MEO) and Geostationary Earth Orbit (GEO) have a potential role in serving as a means to distribute secure keys for encryption among distant endpoints. This dissertation systematically evaluates such a role. The dissertation proposes a layered framework using satellites and fiber optic links that can form a composite system for carrying the information payload and distributing quantum-secure keys for encrypting information in transit. Quantum communications links are currently point-to-point. Considering the concept of global QKD network, there is need for multicast quantum links. Multi casting can be achieved in quantum networks by (a) using multiple wavelengths, or (b) using use specific set of bases. In efforts to develop a composite quantum secure global communication system; this dissertation also introduces the concept of multi-photon tolerant quantum threshold cryptography. The motivation for development of threshold cryptography is that a secret can be encrypted with multiple users and requires multiple users to decrypt. The quantum threshold cryptography is proposed by using idea of multiple bases. This can be considered as step forward towards multiparty quantum communication. This dissertation also proposed layered architecture for key distribution. Concisely, this dissertation proposes the techniques like multicasting in quantum scenario, quantum threshold cryptography to achieve the goal of secured global communication

Physical-Layer Security, Quantum Key Distribution and Post-quantum Cryptography

The growth of data-driven technologies, 5G, and the Internet place enormous pressure on underlying information infrastructure. There exist numerous proposals on how to deal with the possible capacity crunch. However, the security of both optical and wireless networks lags behind reliable and spectrally efficient transmission. Significant achievements have been made recently in the quantum computing arena. Because most conventional cryptography systems rely on computational security, which guarantees the security against an efficient eavesdropper for a limited time, with the advancement in quantum computing this security can be compromised. To solve these problems, various schemes providing perfect/unconditional security have been proposed including physical-layer security (PLS), quantum key distribution (QKD), and post-quantum cryptography. Unfortunately, it is still not clear how to integrate those different proposals with higher level cryptography schemes. So the purpose of the Special Issue entitled “Physical-Layer Security, Quantum Key Distribution and Post-quantum Cryptography” was to integrate these various approaches and enable the next generation of cryptography systems whose security cannot be broken by quantum computers. This book represents the reprint of the papers accepted for publication in the Special Issue

Technologies to Support Authentication in Higher Education:A Study for the UK Joint Information Systems Committee, August 21th, 1996

This report provides a short and limited study, commissioned by JISC, of the technologies available to support authentication, reviews the needs expressed by a set of people contacted for the study, and provides the beginnings of a road-map on how a National system might be established.First a brief overview of the fundamentals of Security technology is provided. As part of the study, we were asked to consult a number of people - particularly from the set of those supported under the JISC Electronic Library initiative. These were supplemented by some people at UKERNA and in Information Services departments in the universities. We present our impressions of the requirements envisioned by the people consulted, and their proposed solutions; with very few exceptions, the needs expressed were very limited, and the solutions limited to specific applications. This reflects, we believe, more the selection of the people consulted, than the true needs of the area. It was also coloured, in our view, by the fact that there was no indication that any finance for a wider initiative might be available.A more detailed review of the current methods of authentication, the needs and the status of different applications follows. This includes a brief discussion about the Standards being developed in the Internet Engineering Task Force in conjunction with the wider deployment of the Internet and the status of infrastructure standardisation and deployment. We consider also a number of applications: electronic mail, the World Wide Web, remote log-in, document security, multimedia conferencing, directories, general network facilities and electronic commerce. A brief discussion of a number of ancillary technical and legal issues follow: this includes smart-cards, directory systems and key escrow. The existence of legal considerations is indicated, but little argument is developed other than the appending of proposed Government legislation. As a final section, we start on a Road Map of how we might proceed to a National authentication infrastructure for Higher Education. We believe that such a system should be distributed in nature, and could well leverage on the investment already made in an X.500 distributed directory system. It is clear that the current technology would need considerable updating; much broader involvement must be achieved from other sectors of the universities for such an initiative to have broad impact. We mention some of the measures that should be undertaken to enable a successful broader applicability. Based on the existence of a National directory system, we then propose a National authentication infrastructure by proposing a system of Certification Authorities, distributed registration and update, and the retention of the certificates in the National directory system. We propose that existing projects in secure E-mail and electronic libraries be asked how they might be modified if such an infrastructure was developed.A substantial distributed infrastructure for authentication could have implication well beyond the university sector. For this reason, it may be possible to co-fund the development and many of the earlier trials from sources outside JISC. We propose that we explore avenues of co-funding both from the British Foresight Programme and from the European Union Telematics programme.<br/