Fixes from notes

chapter-hsms/chapter.tex

@@ -12,11 +12,23 @@ line of defense in such physical security systems goes back more than a century,
 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.
 
-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.
+In this chapter, we will start with a brief history of 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 we will 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. The
+contributions in this chapter are as follows:
+
+\begin{itemize}
+    \item We provide a historical overview of uses of tamper sensing meshes.
+    \item We provide the first large-scale analysis of real devices incorporating tamper sensing meshes in the academic
+        record.
+    \item We create a taxonomy of practical construction techniques and provide both detailed analyis and photos
+        illustrating them.
+    \item From our sample, we extract several design patterns that can be applied to increase the security of a design.
+    \item We note security flaws in several of our samples.
+    \item We provide the results of CT measurements of multiple samples, and we evaluate their impact on tamper sensing
+        mesh security.
+\end{itemize}
 
 \section{The History of Tamper Sensing Meshes}
 
@@ -54,8 +66,9 @@ the widespread adoption of cryptography in commercial applications~\cite{
 
 \subsection{Use by the US Military}
 
-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
+One early practical uses of tamper sensing meshes for information security as opposed to the security of some physical
+good 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
 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
@@ -1255,29 +1268,29 @@ large-area photodiode coupled to a scintillator crystal converting X-ray photons
 \subsection{Application of Inertial HSM technology}
 
 The widespread use of inexpensive but low-security commodity processes shows that in practical applications, cost is
-often prioritized over security. The IHSM approach naturally complements such a system that uses a low-security mesh
-material and increases its security without needing a more advanced mesh material. The beneficial construction
-techniques that we identified above such as the use of multiple, spaced layers and low-contrast trace materials
-complement IHSM technology naturally. The three-dimensional layout of a mesh becomes easier in an IHSM implementation
-since features like corners between mesh panels or gaps between mesh layers in most layouts are protected by the mesh's
-motion. An unintended advantage that results in IHSM implementations over conventional meshes is that they would provide
-a level of intrinsic resistance to X-ray and CT imaging. In contrast to optical cameras in the visible spectrum, X-ray
-image sensors need integration times in the hundreds of milliseconds or longer, which makes them unsuitable to image a
-quickly moving target.
+often prioritized over security. The IHSM approach complements such a system that uses a low-security mesh material and
+increases its security without needing a more advanced mesh material. Construction techniques that improve the security
+of conventional systems such as the use of multiple, spaced layers and low-contrast trace materials can be directly
+applied to IHSM systems. The three-dimensional layout of a mesh becomes easier in an IHSM implementation since features
+like corners between mesh panels or gaps between mesh layers in most layouts are protected by the mesh's motion. An
+unintended advantage that results in IHSM implementations over conventional meshes is that they would provide a level of
+intrinsic resistance to X-ray and CT imaging. In contrast to optical cameras in the visible spectrum, X-ray image
+sensors need integration times in the hundreds of milliseconds or longer, which makes them unsuitable to image a quickly
+moving target.
 
 \section{Conclusion}
 
-In our survey, we have found a wide variety in tamper sensing mesh construction techniques. Meshes are commonly
+In this survey, we have analyzed a wide variety in tamper sensing mesh construction techniques. Meshes are commonly
 implemented as part of both rigid (PCB) and flexible (FPC) circuit boards, either standalone, or as part of a board also
 carrying other components. Silver or carbon trace patterning techniques that are normally used for membrane keyboards
 are also used in some meshes, but are limited in their structure size. The meshes we found in the wild almost never push
 the boundaries of achievable structure size for a given process.
 
 The strongest systems we found combined a mesh with potting such that separating mesh and potting destroyed the mesh's
-traces. Silver printed circuits like they are normally used for keyboard matrices performed particularly well in this
-regard since the silver ink adheres better to some potting compounds than to its plastic carrier substrate. We found
-copper FPCs are commonly used for meshes. Interestingly, they seem to be a poor choice since they are very robust and
-can even be forcibly separated from some potting compounds without destroying their traces.
+traces. Silver or carbon ink printed circuits like they are normally used for keyboard matrices performed particularly
+well in this regard since such inks adheres better to some potting compounds than to its plastic carrier substrate. We
+found copper FPCs are commonly used for meshes. Interestingly, they seem to be a poor choice since they are very robust
+and can even be forcibly separated from some potting compounds without destroying their traces.
 
 The weakest systems we found completely omitted a tamper sensing mesh. Ironically, all of these systems were devices
 marketed as hardware security modules. Given the inexpensive nature of tamper sensing meshes and the high price point of
@@ -1285,7 +1298,7 @@ such devices, we suspect market segmentation as a driving force behind their man
 sensing meshes despite their low cost. The primary security standard that is most often cited for the certification of
 HSMs is the US government's FIPS-140, now in its third
 version~\cite{usnationalinstituteofstandardsandtechnologySecurityRequirementsCryptographic2019}. A peculiarity of this
-standard is that it only requires active tamper sensing meshes in the highest of the four security levels it defeies.
+standard is that it only requires active tamper sensing meshes in the highest of the four security levels it defines.
 Overall, we can conclude that the term ``HSM'' does not imply state-of-the-art physical tamper sensing.
 
 From an academic point of view, the core finding of our survey is that for academic research on mesh manufacturing,