Enabling quantum cryptography in novel network paradigms

Quantum Key Distribution (QKD) is one of the major cryptographic solutions to tackle the security threats associated to future computational advances, in particular those coming from quantum computing. QKD is an Information-Theoretic Secure (ITS) cryptographic primitive that solves the problem of secret key distribution: it is immune to any attack, independently of the computational power that the eavesdropper might have. At the most simple level, QKD can be seen as a source of symmetric secret keys in two separated places. This advantage comes at a price, since QKD is a physical layer technology that depends on the ability to produce, manipulate, transmit and detect signals at the quantum level. It is not an easy technology and current implementations of QKD lack flexibility. They are designed as black-boxes that require a separate ad-hoc network in order to transmit the quantum signals and avoid any interference from classical signals. Such interferences would kill the delicate correlations encoded in the quantum signals that make possible the creation of secret keys in two separate locations. The result is that current QKD systems cannot be used as a part of a telecommunications network. As devices, they are not only expensive by themselves, but also their requirements increase the deployment and operation costs, heavily penalizing its adoption beyond very specific scenarios. While this is happening, current network architectures are already evolving towards novel architectures based on the principles of softwarization and virtualization. These solutions, so called Software-Defined Networking (SDN) and Network Functions Virtualization (NFV) allows for a faster integration of new technologies and services within the network, while bringing flexibility to optimize the network utilization and service allocation. This added flexibility afforded by softwarization, brings also new vulnerabilities that might be extremely dangerous, since the telecommunications network is a critical infrastructure to our modern information society. From the point of view of QKD, these advances in networking are crucial and must be seen as an bidirectional opportunity. On the one hand, the new networking paradigms allow for a real integration of QKD in the telecommunication network. Under this view, the network is no more a set of disparate devices acting as black-boxes with a predominantly autonomous behavior. Now the decisions are taken by a centralized SDN entity that knows the requirements of devices and applications and can optimize the resources, also catering to the specific needs of quantum devices. On the other hand, the new security threats in this model can be effectively tackled by means of QKD. As such, the new network paradigms not only make possible the real integration of quantum devices in the telecommunications network, it also benefits from this integration by increasing its security level using QKD keys. Following these ideas, the aim of this thesis is twofold: the first is to analyze the requirements for the integration of QKD in current networks, more specifically in SDN architectures, with the objective to make easier their integration and deployment, to optimise and to capitalize the QKD network and reduce their time-to-market; the second, to study current and future network scenarios where QKD can provide an additional security layer to make the network safer against today’s threats and the future ones coming from technologies like quantum computing, i.e. creating a quantum-safe network.