QKD WIP

chapter-qkd/chapter.tex

@@ -221,6 +221,7 @@ key storage, network communication and computation costs.
 \todo{research some more policies.}
 
 \section{The Physics of Quantum Computing}
+\todo{missing}
 
 \section{Quantum Key Distribution}
 
@@ -317,7 +318,7 @@ xWDM.}
 \todo{CV-QKD}
 
 \subsection{Relaying}
-% FIXME (one?) term of the art seems to be "repeater"
+\todo{(one?) term of the art seems to be "repeater"}
 
 The No-Cloning Theorem prevents us from using conventional optical amplifiers to extend the range of a single continuous
 QKD link. What remains as ways to extend the range of a QKD link are \emph{relaying} methods, where one QKD link is
@@ -349,7 +350,7 @@ QKD services over complex network topologies.
 
 There exists a large corpus of academic research on the theory of such large-scale QKD networks ranging from the
 technical implementation of management protocols to specialized QKD systems for QKD networks that improve on standard
-two-party QKD in areas such as complexity or performance. % FIXME lots of citations here
+two-party QKD in areas such as complexity or performance. \todo{lots of citations here}
 In the past decades, a number of proof-of-concept QKD networks have been put into practice. None of these systems
 provide any practical utility yet, and their raison d'être lies in the political realm more than it arises out of
 technical necessity considering that any of today's city-scale demonstrations can easily be simulated more compactly in
@@ -388,13 +389,77 @@ The second prediction we can make is that any practical QKD network will have to
 distances. While in certain specialized applications such as the proposed financial QKD network in Switzerland
 \todo{citation on swiss deployment} smaller, isolated networks are conceivable, in every telecommunication system from
 the telegraph through the telephone system and up to the internet it has been shown conclusively that there is a real
-demand for a unified, global interconnected network. \todo{citation on historic networks}
+demand for a global, interconnected network\footnote{In fact, history repeats, and the enthusiasm that Quantum Key
+Distribution networks have kindled parallels the one that the first trans-atlantic telegraph cables brought forth as
+described by \textcite{mullerWiringWorldSocial2016}. Both parallel not just in the extensive promises attributed to
+their respective technologies, but also in the facade of technological determinism that in both cases hides a number of
+social and political motivations.}\cite{mullerWiringWorldSocial2016}. \todo{at least one more citation on historic
+networks}
 
 In this section, we will outline a solution that provides practical, end-to-end security in large-scale QKD networks by
 delegating the hardware trust issue of QKD relays to Inertial Hardware Security Modules. The primary design challenges
 we will address are the systems' overall envelope design, optical passthroughs, and matching the cryptographic
 assumptions behind the IHSM's heartbeat and alarm subsystem to those of the QKD application.
 
+\subsection{The anatomy of a QKD node}
+
+With the exception of special cases such as the middle node in a MDI-QKD system, a general QKD relay contains the same
+components that the endpoint of a QKD connection uses. Only in a QKD relay, two transceivers are connected back-to-back
+to one another. QKD provides physical security for the photons traversing the fiber that forms the systme's channel, and
+the security envelope of the system begins where this fiber is terminated in the power splitters, single-photon
+deetctors, lasers, and interferometers of the QKD transmitter and receiver. To process the raw measurements of the QKD
+system into a usable stream of secret key bits, in addition to these components implementing the physics of the QKD
+system, a classical computer is needed. On top of the remote monitoring and management tasks that any piece of
+networking equipment is expected to perform nowadays, this computer is tasked with the information reconciliation and
+privacy amplification that form the information-theoretic part of the QKD system. Since this computer necesesarily
+handles secret key bits in their plain text form, it, too, must be inside the relay node's physical protection envelope.
+
+\subsection{Physical requirements of QKD transceivers}
+
+\paragraph{Physical dimensions.}
+At this point, a number of commercial systems promising QKD exist. Common QKD protocols do not require any particularly
+large or power-hungry components, and so commercial systems have generally adopted the 19 Inch rackmount enclosure
+standard that is common to modern telecommunications equipment, with a width of $\approx\qty{50}{\centi\meter}$, a
+height between $\approx\qtyrange{4}{30}{\centi\meter}$ and a depth below $\approx\qty{100}{\centi\meter}$.\todo{Re-check
+these shortly before submission}. While something of this size would be infeasible to protect with the security mesh of
+a traditional hardware security module, placed vertically, even without modifications any of these systems are well
+within an envelope that can be protected with a single IHSM cage.
+
+\paragraph{Power supply.}
+QKD systems do not contain any particularly power-hungry components. Unlike quantum computers, most of the signal path
+is optical, and as such can be implemented with room-temperature fiber-optic components. Only the single-photon
+detectors may require cooling in some systems, but unlike something like an ion trap quantum computer's processor,
+energy-intensive deep cryogenic cooling is not necessary. Most manufacturers don't quote the power requirements of their
+systems, but we were able to find that IDQuantique specifies their QKD systems to be able to run off a single
+\qty{300}{\watt} power supply. In an intertial HSM, power up to several \unit{\kilo\watt} can easily be transferred to
+the payload with through-axis cables.
+
+\paragraph{Cooling.}
+While the few hundred watt of power that QKD systems require could easily be transported through the mesh of a a
+traditional HSM as well, cooling that amount of thermal load purely by heat conduction through centimeters of epoxy
+resin would make implementation infeasible in traditional HSM. In an IHSM, on the other hand, up to several
+\unit{\kilo\watt} can easily be dissipated through forced-air cooling since the rotating security mesh can have an
+arbitrary amount of longitudinal slots or holes.
+
+\paragraph{Data and signals.}
+A QKD transceiver has a number of ports in addition the port for the fiber optic quantum channel. Depending on the
+system, one or more additional optical links may be necessary for clock distribution, allowing both endpoints to tune
+their lasers into precise alignment. QKD protocols require a classical link used for information reconciliation, which
+along with the key stream output and management links requires one or more classical network ports.
+
+In a QKD relay node, the key stream never leaves the security envelope. The management and information reconciliation
+links can be combined into a single, classical network link, requiring a single fiber when using a standard wavelength
+division multiplexing transceiver. The QKD link's clock channel and the quantum channel require a dedicated fiber each,
+adding up to a total of five fibers for a uni-directional QKD relay, or nine fibers for a bidirectional one. Since fiber
+pigtails have an outer diameter of usually about \qty{1}{\milli\meter}, this amount of fibers can easily be fed through
+an IHSM's axis of rotation. The mechanical challenge in such a multi-fiber signal and data feedthrough is to observe the
+fiber's minimum bending radius, which for common fibers is usually in the range of
+\qtyrange{5}{10}{\milli\meter}\todo{Provide citation on bend radius. Maybe a small table of products by a few vendors?}.
+For detailed passthrough designs, we refer the reader to Chapter FIXME of this thesis.\todo{Actually write the chapter,
+then cross-link here.}
+
+
+
 \section{Outlook}
 
 \newpage