Small fixes in survey chapter

chapter-hsms/chapter.tex

@@ -6,35 +6,35 @@
 
 \chaptertitle{Active Tamper Sensing in the Wild}
 
-Inertial Hardware Security Modules are the latest link in a series o developments bringing hardware security primitives
-from niche military cipher machines to mass-market applications. The tamper-sensing technology that forms the primary
-line of defense in such physical security systems goes back more than a century, with the earliest tamper-sensing meshes
+Inertial Hardware Security Modules are the latest link in a series of developments bringing hardware security primitives
+from niche military cipher machines to mass-market applications. The tamper sensing technology that forms the primary
+line of defense in such physical security systems goes back more than a century, with the earliest tamper sensing meshes
 being used in the late 19\textsuperscript{th} century, around the widespread commercialization of electricity. Today,
-active tamper-sensing meshes are used in a wide array of devices ranging from card payment terminals to atomic bombs.
+active tamper sensing meshes are used in a wide array of devices ranging from card payment terminals to atomic bombs.
 
-In this chapter, we will start with a brief history of secure hardware with a particular focus on tamper-sensing meshes.
-Complementing our historical analysis, we will present the results of a survey of a range of real-world devices using
-tamper-sensing meshes and analyze their implementation. We will analyze the gaps left by the current state of the
-industry, and evaluate how Inertial HSMs could close these gaps to make secure hardware accessible to a wider range of
-applications. We will start with a brief history of secure hardware with a particular focus on tamper-sensing meshes.
+In this chapter, we will start with a brief history of secure hardware with a particular focus on tamper sensing meshes.
+Complementing our historical analysis, we will present the results of a survey of a range of real-world devices that use
+tamper sensing meshes and analyze their implementation. We will analyze the gaps left by the current state of the art in
+commercial practice, and evaluate how Inertial HSMs could close these gaps to make secure hardware accessible to a wider
+range of applications.
 
 \section{The History of Tamper Sensing Meshes}
 
-Tamper-sensing meshes offer many degrees of freedom in their design ranging from the precise conductor layout, through
+tamper sensing meshes offer many degrees of freedom in their design ranging from the precise conductor layout, through
 the manufacturing technology of the mesh and how it is wrapped around the payload during manufacturing up to their
-monitoring circuitry. As a result, manufacturers across application domains from datacenter appliance HSMs through card
-payment terminals have historically used patents on parts of their tamper-sensing mesh implementations as a means to
+monitoring circuitry. As a result, manufacturers across application domains from datacenter appliance HSMs to card
+payment terminals have historically used patents on parts of their tamper sensing mesh implementations as a means to
 prevent copying of their designs~\cite{
     razaghiCircuitBoardHold2019,
     heitmannTamperBarrierElectronic2005,
     clarkTamperDetectionSystem2005,
     heitmannMethodMakingTamper2009,
     perreaultSystemMethodInstalling2005,
-}. The basic principle of modern tamper-sensing meshes, preventing physical intrusion using an embedded looped conductor
-to cover a surface traces back as far as at least 1870~\cite{
+}. The basic principle of modern tamper sensing meshes, preventing physical intrusion using an embedded looped conductor
+to cover a surface, traces back at least as far as 1870~\cite{
     ImprovementProtectingSafes1870,
     ImprovementElectromagneticEnvelopes1870}, when it was applied to the protection of bank vaults from robbers
-attempting to dig, drill and saw through the vault's floor and walls. Even multi-layer, orthogonal tamper-sensing meshes
+attempting to dig, drill and saw through the vault's floor and walls. Even multi-layer, orthogonal tamper sensing meshes
 are documented as far back as 1902~\cite{suttonElectricallyprotectedStructure1902}. Using printed circuits instead of
 wires for this purpose occurs in literature as soon as printed circuit technology finds widespread commercial adoption
 in the 1960ies~\cite{hamPrintedcircuitTypeSecurity1971}. The history of more HSM-like devices begins in the 1990ies with
@@ -56,7 +56,7 @@ the widespread adoption of cryptography in commercial applications~\cite{
 
 One of the earliest practical uses of tamper sensing meshes is documented in notes on a series of lectures given by
 Dr.~David~G. Boak, a specialist in communications security and signal intelligence at the US National Security
-Agency\cite{nsaHistoryUSCommunications1973,nsaHistoryUSCommunications1981}. In this lecture series, Boak mentions that
+Agency~\cite{nsaHistoryUSCommunications1973,nsaHistoryUSCommunications1981}. In this lecture series, Boak mentions that
 around World War \RN{2}, the US became concerned about the security of their ciphering machines, which at the time were
 large, fridge-sized electro-mechanical contraptions. Initially, simple safes were used to protect those
 devices---however, as Boak notes, the US was well aware that they could not build a safe that a well-equipped specialist
@@ -68,7 +68,7 @@ exciting--exploding the device.
 
 \subsection{Use in Nuclear Weapons}
 
-Communications security was not the earliest use of tamper-sensing membranes in the US military, with Boak mentioning
+Communications security was not the earliest use of tamper sensing membranes in the US military, with Boak mentioning
 HSMs still being under development in the second volume of the lecture series, dated 1972. An earlier reference to such
 systems can be found in literature on Permissive Action Links (PALs) for nuclear weapons. In US military terminology, a
 PAL is a chain of locked, tamper-proof systems required to trigger the detonation of a nuclear weapon. PALs were
@@ -83,13 +83,13 @@ explosion that the weapon is capable of. This goal is achievable in practice sin
 sensitive to the timing of their primary explosive charges, as the nuclear payload only produces a full-scale detonation
 when triggered in just the right way.
 
-While it is difficult to date, \textcite{carterManagingNuclearOperations1987} specifically mention a tamper-sensing
+While it is difficult to date, \textcite{carterManagingNuclearOperations1987} specifically mention a tamper sensing
 membrane being used in US PALs. Given the nature of the matter, it is safe to assume that this technology will have been
 in use for some years at the point it was being discussed in an unclassified, civilian book on nuclear armament control.
 
 \subsection{Use in Nuclear Safeguards}
 
-Besides being used in nuclear weapons, tamper-sensing systems have another, more peaceful application in the nuclear
+Besides being used in nuclear weapons, tamper sensing systems have another, more peaceful application in the nuclear
 field. In 1957, the International Atomic Energy Agency (IAEA) was founded to coordinate and verify that civilian nuclear
 energy installations are not used for military purposes. A core part of the IAEA's tasks is observing the operations at
 civilian nuclear installations through inspections and through a variety of permanently deployed sensors to track the
@@ -101,10 +101,10 @@ extensive use of tamper-indicating enclosures and of seals. In both systems, the
 seal is treated similarly to what these days, in computing we call a Physically Uncloneable Function. The enclosure or
 seal is manufactured in a process that leaves an unpredictable and uncontrollable pattern of manufacturing variations
 such as surface imperfections. A process used in the IAEA is to package devices in aluminium enclosures passivated in a
-brigh color, which leaves a random, microscopic pattern of pits in the surface from the etching step. Before such a
+bright color, which leaves a random, microscopic pattern of pits in the surface from the etching step. Before such a
 device is deployed in the field, it is precisely measured from all sides. Later on, after field deployment, its
 integrity can then be checked by comparing its current state to these initial measurements. The underlying assumption is
-that drilling or cutting into something like a steel enclosure will leave detectable traces, and that perfectly
+that drilling or cutting into something like a metal enclosure will leave detectable traces, and that perfectly
 replicating an object including features such as minute surface imperfections is infeasible even to a nation
 state~\cite{iaea2011}.
 
@@ -114,7 +114,7 @@ indication, which we conventionally call tamper evidence. Tamper indicating devi
 aforementioned uniquely characterizable enclosures, which IAEA terminology calls intrinsically tamper-indicating. An
 example for an active tamper indicating device would be a seismic sensor at the bottom of a borehole that has been
 back-filled with concrete such that any attempt to reach the sensor would be well-visible in the sensor's own
-readings~\cite{simmonsHowInsureThat1988}
+readings~\cite{simmonsHowInsureThat1988}.
 
 With smarter electronics becoming more affordable in both monetary and in power budget, over the decades, other active
 tamper sensors have received attention as well. The IAEA reports on attempts at burying sensors such as piezoelectric
@@ -137,22 +137,23 @@ HSMs are used for highly sensitive operations even outside of the financial indu
 hampered by their high cost. Such applications include key management in the TLS certificate infrastructure. In this
 chapter, we will analyze a commercial HSM that was used in the key management infrastructure of a premium TV provider.
 
-Beyond finance, tamper-sensing meshes have found applications in a variety of other use cases as well. For instance, we
+Beyond finance, tamper sensing meshes have found applications in a variety of other use cases as well. For instance, we
 have found them being used in mail franking machines to protect the credit counter and franking data, with one such unit
-analyzed in this chapter. Furthermore, we have identified at least one model of key safe that in Germany is mounted
-externally on public buildings to provide keys to emergency services, and which includes a tamper sensing mesh on its
-outside-facing wall to detect attempts at drilling into it. Finally, we have found a processing unit used in a series of
-mid-2000s era slot machines in Germany that includes a tamper-sensing mesh, presumably to prevent modification or
+analyzed in this chapter. Furthermore, we have identified several models of key safes that in Germany are mounted
+externally on public buildings to provide keys to emergency services, and which include tamper sensing meshes on their
+door and interior walls to detect attempts at drilling into them~\cite{SD04203RB25D5,
+krusesicherheitssystemeDatenblattKRUSEFWSchlusseldepot2018}. Finally, we have found a processing unit used in a series
+of mid-2000s era slot machines in Germany that includes a tamper sensing mesh, presumably to prevent modification or
 cloning. This device will also be analyzed later in this chapter.
 
-\section{Tamper-Sensing Mesh Design Principles}
+\section{tamper sensing Mesh Design Principles}
 
-%\subsection{Tamper-sensing Mesh Manufacturing}
+%\subsection{tamper sensing Mesh Manufacturing}
 
 The manufacturing technology of a tamper sensing mesh is a critical factor in its security. While in many applications,
 meshes manufactured from off-the-shelf processes such as Flexible Printed Circuit (FPC) processes are used, these
 processes tend to be optimzed to maximize the robustness of the produced circuits to mechanical stress. In contrast, the
-ideal tamper-sensing mesh is exactly as robust as it needs to be not to be destroyed accidentially during normal
+ideal tamper sensing mesh is exactly as robust as it needs to be not to be destroyed accidentially during normal
 handling, but should not be more robust than that. As a result, more secure meshes tend to be manufactured in bespoke
 manufacturing processes~\cite{
     immlerBTREPIDBatterylessTamperresistant2018,
@@ -160,7 +161,7 @@ manufacturing processes~\cite{
     ImprovementProtectingSafes1870}.
 % TODO cite hennigApparatusMethodComprising2020 and obermaierPUFfilmMethodProducing2023 on immler et al PUF tech
 
-One more widely cited tamper-sensing mesh implementation is a commercial product developed by IBM in collaboration with
+One more widely cited tamper sensing mesh implementation is a commercial product developed by IBM in collaboration with
 chemical company W.\ L.\ Gore \& Asscociates Inc.\ and used in IBM's datacenter HSM products up to approximately 2020.
 This mesh design uses a stack of multiple layers of a clear, flexible plastic substrate on which carbon-based traces are
 printed. Vias, i.e. contacts between layers, are made by laser cutting small holes into the substrate before the traces
@@ -178,8 +179,8 @@ basic construction and layout has not changed much since the early 1990ies~\cite
 
 \subsection{Monitoring Circuit Approaches}
 
-Tamper-sensing meshes are most effective when they are continuously monitored using a backup power supply when the
-larger system is powered off. In practice, the main challenge with continuous monitoring of tamper-sensing meshes is in
+tamper sensing meshes are most effective when they are continuously monitored using a backup power supply while the rest
+of the system is powered off. In practice, the main challenge with continuous monitoring of tamper sensing meshes is in
 the design of the monitoring circuit. A large portion of industry attention has been spent on designing low-power
 monitoring circuits that are sensitive to tampering with the mesh while using little enough power to enable years of
 operation from a battery. Commonly, one or two cylindrical or large coin cell Lithium primary batteries are used,
@@ -193,7 +194,7 @@ To achieve low power consumption, a popular technique known since at least
 today~\cite{cesanaTamperResistantCard2001,razaghiCircuitBoardHold2019} is to measure the deviation of the mesh's
 end-to-end ohmic resistance from its baseline value. This measurement can be implemented either by directly comparing a
 mesh trace's resistance with a reference resistor, or using a wheatstone bridge. Using a bridge circuit was already used
-in early tamper-sensing mesh implementations~\cite{
+in early tamper sensing mesh implementations~\cite{
     ElektrischeSicherheitseinrichtungSchutze1932,
     hamPrintedcircuitTypeSecurity1971,
     dalphinEnceinteProtegeeAvec1987,
@@ -201,7 +202,7 @@ in early tamper-sensing mesh implementations~\cite{
 
 \subsection{Other Tamper Sensing Techniques}
 
-Besides tamper-sensing meshes, environmental sensors such as temperature or light sensors are frequently used as a
+Besides tamper sensing meshes, environmental sensors such as temperature or light sensors are frequently used as a
 secondary line of defence in HSMs and similar devices. By placing such sensors in the device and verifying the device is
 within its nominal operating environment, tampering can be made less convenient. Modern security standards often mandate
 the implementation of at least a temperature sensor to prevent cold-boot attacks on a device. A multitude of other
@@ -221,7 +222,7 @@ meshes in civil applications was likely catalyzed by two advancements in electro
 became less expensive and more integrated reducing the cost overhead of tamper sensing circuits. Second, the mass-scale
 adoption of PCB and Flexible Printed Circuit (FPC) production processes enabled their use as inexpensive,
 high-resolution substrates for such meshes. In this section, we will examine a large sample of recent devices that
-include tamper-sensing meshes to gain an understanding of how they are implemented, and what security level they are
+include tamper sensing meshes to gain an understanding of how they are implemented, and what security level they are
 targeted towards. Since we were unable to acquire a nuclear weapon for our research, we limited our survey to commercial
 devices with a focus on card payment terminals, which represent the most varied class of device incorporating such
 meshes.
@@ -317,8 +318,8 @@ Figure~\ref{fig_hsm_survey_sample_internal_pics}.
         \surveypic{28}{survey_diag_S28.jpg}&
         \surveypic{29}{survey_diag_S29.jpg}&
         \surveypic{30}{survey_diag_S30.jpg}&
-        \surveypic{30}{survey_diag_S31.jpg}\\
-        \surveypic{30}{survey_diag_S32.jpg}&
+        \surveypic{31}{survey_diag_S31.jpg}\\
+        \surveypic{32}{survey_diag_S32.jpg}&
     \end{tabular}
     \caption{External photos of all survey samples}
     \label{fig_hsm_survey_sample_pics}
@@ -343,8 +344,8 @@ standards~\cite{pcisecuritystandardscouncilPaymentCardIndustry2025}. As a result
 safeguard weak symmetric keys, compensating for the systems' modest cryptographic security.
 
 Since card payment terminals are widely deployed, many different models from various manufacturers are available. Each
-manufacturer tends to have their own, patented tamper-sensing implementation. Being manufactured at scale, card payment
-terminals are cost-sensitive devices, which is reflected in the construction of their tamper-sensing implementations.
+manufacturer tends to have their own, patented tamper sensing implementation. Being manufactured at scale, card payment
+terminals are cost-sensitive devices, which is reflected in the construction of their tamper sensing implementations.
 
 \subsubsection{HSM Appliances}
 
@@ -379,7 +380,7 @@ with the customer's card passes through an end-to-end encrypted channel from the
 smartcard IC, the customer must necessarily enter their pin in plain text. To prevent leakage of the plaintext PIN, the
 PIN is encrypted inside the PIN pad itself. To this end, the PIN pad contains a microcontroller handling the encryption.
 Often, both the circuit board containing the PIN pad's keyboard matrix and this microcontroller are shielded by a
-tamper-sensing mesh to prevent physical attacks such as the installation of a skimming device that would record and
+tamper sensing mesh to prevent physical attacks such as the installation of a skimming device that would record and
 transmit the plaintex PIN.
 
 We acquired three different EPPs for analysis: Two designed by Sagem and apparently re-sold as a whitelabel product by
@@ -388,7 +389,7 @@ cases.
 
 \subsubsection{Other miscellaneous devices}
 
-Sometimes, tamper-sensing meshes show up in other types of devices. We acquired two such devices. First, we acquired a
+Sometimes, tamper sensing meshes show up in other types of devices. We acquired two such devices. First, we acquired a
 Neopost mail franking machine, a type of device that is used to directly print a code on an envelope that replaces a
 conventional postage stamp. Since in businesses handling large volumes of mail these devices were routinely charged with
 large sums of money in postage, such devices have security features ranging from physical seals on their enclosure to
@@ -398,7 +399,7 @@ specimen only contained a sturdy cast zinc case that was welded shut with a spri
 miscellaneous device we found is a broken CPU module from a German slot machine manufacturer. While it would be
 reasonable to assume this type of device might include active tamper sensing features to enforce state gambling
 regulations, other slot machine manufacturers seem not to use tamper sensing in their systems so the more likely reason
-is DRM. Our specimen included both a tamper-sensing mesh as well as a semiconductor junction light sensor inside of a
+is DRM. Our specimen included both a tamper sensing mesh as well as a semiconductor junction light sensor inside of a
 sealed sheet metal enclosure.
 
 \subsection{Methodology}
@@ -406,7 +407,7 @@ sealed sheet metal enclosure.
 We proceeded by first photographing every test specimen from multiple angles, then disassembling them. After
 disassembly, we photographed each major component. Figure~\ref{fig_hsm_survey_sample_internal_pics} shows a selection of
 these photos showing the major internal components of the devices. After photos were taken, we proceeded with
-destructive techniques where necessary to obtain microscope photos of each tamper-sensing mesh component. PCBs were
+destructive techniques where necessary to obtain microscope photos of each tamper sensing mesh component. PCBs were
 sectioned using a sanding drum attachment on a Dremel rotary tool. Potted modules were disassembled using milling,
 cutting and prying, and applying heat from a heat gun as necessary to soften polymer compounds and to break glue joints.
 
@@ -459,7 +460,7 @@ supplementary material to this thesis.
 
 \subsubsection{Mesh materials.}
 We found meshes constructed from rigid PCBs as well as a number of Flexible Printed Circuit (FPC) processes.
-Tamper-sensing meshes constructed from PCBs sometimes used parts of an existing PCB, and sometimes additional PCBs only
+tamper sensing meshes constructed from PCBs sometimes used parts of an existing PCB, and sometimes additional PCBs only
 containing a mesh were added. Sometimes, multiple rigid PCB meshes were assembled in a house of cards fashion to enclose
 part of a device. For flexible meshes, with the exception of the Utimaco HSM appliance's HSM card that used an
 off-the-shelf Gore tamper sensing mesh foil were all clearly manufactured either entirely or mostly in standard
@@ -500,7 +501,7 @@ printed foil meshes was coarser at between \qtyrange{500}{3000}{\micro\meter}.
     \label{hsm_fig_mesh_layout}
 \end{figure}
 
-A key goal in tamper-sensing mesh design is to avoid any gaps in coverage. In single-layer meshes, gaps between adjacent
+A key goal in tamper sensing mesh design is to avoid any gaps in coverage. In single-layer meshes, gaps between adjacent
 mesh traces cannot be avoided, and provide an easy approach for an attack. In multi-layer meshes, these structure
 size-dependent gaps can be mitigated in multiple ways as shown in Figure~\ref{hsm_fig_mesh_layout}.
 
@@ -515,7 +516,7 @@ mesh pattern mostly orthogonal on the mesh's two layers as shown in Figure~\ref{
 this leads to a larger amount of gaps compared to offset patterns as described above, it also reduces the largest gap
 size to about one structure size by one structure size.
 
-\paragraph{Combined approaches.} Figure~\ref{hsm_fig_mesh_layout_utimaco} shows the layout of a Gore tamper-sensing mesh
+\paragraph{Combined approaches.} Figure~\ref{hsm_fig_mesh_layout_utimaco} shows the layout of a Gore tamper sensing mesh
 foil used in an Utimaco HSM. This mesh consists of two foil layers bonded to each other. The outer foil is patterned on
 both sides with a sparse pattern of thin serpentine traces with the patterns on both layers being orthogonal to each
 other. Both patterns are oriented at a \qty{45}{\degree} angle relative to the sides of the rectangular enclosed volume.
@@ -568,23 +569,23 @@ structure size, which limits the possible angles an attack tool could be inserte
     \label{hsm_fig_materials}
 \end{figure}
 
-Regular Printed Circuit Boards are frequently used to implement tamper-sensing meshes as shown in
+Regular Printed Circuit Boards are frequently used to implement tamper sensing meshes as shown in
 Figure~\ref{hsm_fig_materials_pcb_rigid}. PCB production is a highly advanced, large-scale industry and PCBs are
 inexpensive, commodity products. PCBs can be manufactured with many layers, at almost arbitrary total thickness, and
 offer small structure sizes enabling the creation of fine features down to approximately \qty{100}{\micro\meter} even on
-commodity processes. The primary disadvantage of using PCBs to implement tamper-sensing meshes is that PCBs are
+commodity processes. The primary disadvantage of using PCBs to implement tamper sensing meshes is that PCBs are
 fundamentally designed to be as robust as possible. The traces on the top of a PCB are etched from a thick (usually
 \qty{35}{\micro\meter} on the outer layers) copper foil adhered to the PCB substrate. As a result, the PCB and the
 traces on its surface are easy to manipulate by hand using tools like knives and techniques like soldering. For a
-tamper-sensing mesh, trace patterns manufactured to be more fragile might be advantageous. Additionally, standard PCBs
-are made using a rigid FR-4 fiberglass/epoxy substrate. Since a tamper-sensing mesh must often enclose all sides of a
+tamper sensing mesh, trace patterns manufactured to be more fragile might be advantageous. Additionally, standard PCBs
+are made using a rigid FR-4 fiberglass/epoxy substrate. Since a tamper sensing mesh must often enclose all sides of a
 payload, flexible foils offer benefits over rigid PCBs.
 
 Figure~\ref{hsm_fig_materials_pcb_flex} shows a Flexible Printed Circuits (FPCs) produced in a standard commercial
 process similar to PCB production. In FPCs, a copper foil adhered to a substrate is etched, but the substrate here
 usually is a thin foil made from polyimide, an orange, temperature-resistant polymer that survives common reflow (hot
 air) soldering temperatures. In contrast to rigid PCBs, FPCs are usually limited to no more than four layers before
-losing flexibility. Flexible PCBs are often used for tamper-sensing meshes that wrap around a payload, but they come
+losing flexibility. Flexible PCBs are often used for tamper sensing meshes that wrap around a payload, but they come
 with the same limitation as standard PCBs: Due to their robust substrate and thick copper layers, they are easily
 manipulated by hand.
 
@@ -595,7 +596,7 @@ small conductive particles suspended in a hardening binder. Common conductive in
 Silver-based inks offer lower resistance compared to carbon-based inks, but are prone to surface oxitation and as such
 are not suitable for contacts. As such, they are often combined with a carbon ink used in contact areas. Carbon-based
 inks have high resistance, and can be used to create embedded resistors. The circuit shown in
-Figure~\ref{hsm_fig_materials_silver_ink} contains a tamper-sensing mesh on a lower layer, and a keypad matrix with
+Figure~\ref{hsm_fig_materials_silver_ink} contains a tamper sensing mesh on a lower layer, and a keypad matrix with
 carbon contacts on its surface.
 
 Figure~\ref{hsm_fig_materials_gold_lds} shows part of a mesh and a contact created using Laser Direct Structuring and
@@ -646,11 +647,11 @@ contacts. They must be contacted using a soft material, usually an elastomeric c
         \caption{}
         \label{hsm_fig_connector_dome}
     \end{subfigure}
-    \caption[Mesh connecting methods]{Connecting methods used between tamper-sensing mesh assemblies and their base PCBs}
+    \caption[Mesh connecting methods]{Connecting methods used between tamper sensing mesh assemblies and their base PCBs}
     \label{hsm_fig_connector}
 \end{figure}
 
-In our survey, we found a wide variety of connecting methods used to connect tamper-sensing mesh assemblies with their
+In our survey, we found a wide variety of connecting methods used to connect tamper sensing mesh assemblies with their
 base PCBs with a selection shown in Figure~\ref{hsm_fig_connector}. Both rigid PCBs and FPCs can be soldered directly to
 a PCB using either a Land Grid Array (LGA) technique where pads on both PCBs are soldered facing each other, or using
 \emph{castellated} edges, where pads on the base PCB are soldered sideways to holes on the top PCB that have been milled
@@ -664,15 +665,15 @@ on the FPC. Both FPCs and rigid PCBs can be used with standard board-to-board st
 visible in the center of Figure~\ref{hsm_fig_connector_stack}, but their use on FPCs requires a stiffener on the FPC's
 back side to ensure the solder joints don't break from mechanical stress when connecting or disconnecting.
 
-In our survey, we frequently found elastomeric connectors used to connect to both flexible and rigid tamper-sensing mesh
+In our survey, we frequently found elastomeric connectors used to connect to both flexible and rigid tamper sensing mesh
 assemblies. Elastomeric connectors such as the one shown in the center of Figure~\ref{hsm_fig_connector_elastomeric} are
 usually used in LCD construction to contact a PCB to the LCD's Indium Tin Oxide (ITO)-coated conductive glass, but they
-can be used between any two parallel, conductive surfaces\cite{andreaElectronicConnectorBook2022}. Elastomeric
+can be used between any two parallel, conductive surfaces~\cite{andreaElectronicConnectorBook2022}. Elastomeric
 connectors consist of two insulating elastic polymer layers on the outside, with a thin strip of fine, alternating
 conductive and insulating elastic polymer layers sandwiched in between. In Figure~\ref{hsm_fig_connector_elastomeric}
 the outer insulating layers are the blue polymer, and the alternating pattern can be seen embedded in their middle. The
 fine alternating pattern mates to much larger pads on the two contact surfaces, ensuring that adjacent contacts are
-electrically insulated. In tamper-sensing mesh applications, elastomeric connectors provide an intrinsic disassembly
+electrically insulated. In tamper sensing mesh applications, elastomeric connectors provide an intrinsic disassembly
 detection since they require continuous pressure to maintain electrical contact. In the top part of
 Figure~\ref{hsm_fig_connector_stack}, a land pattern for an elastomeric connector is visible.
 
@@ -689,7 +690,7 @@ to a base PCB. Here, a tactile metal dome intended to be used for creating butto
 connect the mesh to the base PCB.
 
 An alternative to soldering and elastomeric connectors that we did not observe during our survey but that deserves
-mention here is Anisotropic Conductive Film (ACF)\cite{huangHardwareHackerAdventures2019}. Similar to elastomeric
+mention here is Anisotropic Conductive Film (ACF)~\cite{huangHardwareHackerAdventures2019}. Similar to elastomeric
 connectors, ACF is industrially used to contact flexible PCBs to ITO-coated glass in TFT displays. ACF comes as a
 double-sided tape that is bonded using pressure and sometimes high temperatures, and creates a connection between
 conductive surfaces on both sides of the tape. This connection has an anisotropic nature, meaning that the tape only
@@ -896,9 +897,9 @@ mesh.
 
 % FIXME intro here
 
-%\subsection{Tamper-sensing meshes then and now}
+%\subsection{tamper sensing meshes then and now}
 
-Concluding both our patent research and our experimental survey, we find that tamper-sensing meshes have been a
+Concluding both our patent research and our experimental survey, we find that tamper sensing meshes have been a
 commonplace technology throughout the past 150 years. While mesh manufacturing technology has experienced some
 advancements from historical wire-wound meshes to modern meshes always being constructed in printed circuit processes,
 mesh monitoring approaches have received surprisingly little attention through the centuries and even in recent,
@@ -908,7 +909,7 @@ considered sufficient by manufacturers.
 
 \subsection{Mesh construction techniques}
 
-We found that in almost all cases, practical tamper-sensing meshes are constructed using standard manufacturing
+We found that in almost all cases, practical tamper sensing meshes are constructed using standard manufacturing
 processes. In some card payment terminals, we found meshes that used slightly customized standard processes and e.g.
 integrated a mesh layer produced in a carbon printing process into a membrane keypad, but customizations were minimal.
 We only found one mesh manufactured in a bespoke process in the datacenter HSM appliance we examined, and that bespoke
@@ -924,7 +925,7 @@ based around a number of voltage comparators.
 \subsection{Computed Tomography Imaging}
 
 CT imaging presents a serious threat to any HSM design that relies on its mesh layout remaining secret. For instance,
-the Gore tamper-sensing mesh product used in IBM and Utimaco HSMs includes a feature where after production, small vias
+the Gore tamper sensing mesh product used in IBM and Utimaco HSMs includes a feature where after production, small vias
 are lasered into a specially preparte area on the mesh foil to randomize the connection pattern of the mesh on a
 unit-by-unit basis. CT imaging could be used to discern this type of customization. Furthermore, CT imaging can be used
 to provide sub-millimeter accurate positioning for an attack, even if the sample to be attacked has large production
@@ -949,7 +950,7 @@ solution.
 \paragraph{Use of X-ray attenuating materials.}
 We found that placing any highly X-ray attenuating material in the HSM makes CT imaging more difficult.
 Figure~\ref{hsm_fig_utimaco_ct} shows a CT image taken from an Utimaco HSM. The device has two thick metal layers with a
-potting resin and the tamper-sensing mesh in between, so high-energy X-rays were necessary to penetrate both metal
+potting resin and the tamper sensing mesh in between, so high-energy X-rays were necessary to penetrate both metal
 layers and image the device. As a result, the contrast on X-ray-transparent features like polymers is low. In
 comparison, the Ingenico sample was easy to image since it consisted of a PCB wrapped with a mesh foil and encased in
 resin inside of an injection-molded plastic enclosure. Thus, we were able to image it at a low X-ray energy and we were
@@ -1011,7 +1012,7 @@ Form an engineering point of view, we observe that across application domains, t
 construction techniques. Implementing such a system that matches the security of other systems seen in the wild should
 be achievable to most engineers.
 
-We find that the IHSM approach is a natural extension of the state of the art that we saw reflected in tamper-sensing
+We find that the IHSM approach is a natural extension of the state of the art that we saw reflected in tamper sensing
 mesh implementations in the field, and that the construction techniques that have been applied to improve their security
 can be carried over to IHSM implementations.