Add lots of patent history detail

chapter-hsms/chapter.tex

@@ -139,9 +139,58 @@ The design of these IBM/Gore meshes is documented in an extensive list of patent
 
 \subsection{Tamper-sensing Mesh Monitoring}
 
+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
+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,
+providing in the order of \qtyrange{10}{20}{\watt\hour} over their lifetime. Broken down to an unpowered storage life of
+e.g.\ 5 years, this corresponds to a maximum average power consumption of \qty{450}{\micro\watt}.
+
+% FIXME cite patent US20010056542A1, maybe others?
+% relevant categories: (H01L23/576),  (G06K19/07372)
+% keyword: wire covering
+% FIXME US10251260B1, US9730315B1 (both square) mention wheatstone bridge
+% FIXME DE2656349A1 mentions bridge circuit but applied to a fence(!)
+To achieve low power consumption, a popular technique known since at least 1902
+% FIXME cite US708093A
+and still used today
+% FIXME cite section on utimaco / gore mesh, cite US20010056542A1 (ibm), US10251260B1, US9730315B1 (square)
+is to measure the mesh's deviation 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.
+% FIXME cite DE559905C
+This technique, known since at least 1929, is still used in modern HSMs for its simple implementation: Comparators do no
+need a lot of power, and similar to the layout of a strain gauge, the wheatstone bridge circuit can be implemented using
+the mesh's traces. When all traces are interleaved, this also provides some degree of intrinsic temperature
+compensation.
+
+% FIXME US10321589B2 cites comparators
+
+% US587931A (1897) describes overlapping structure
+% FIXME US7345497B2 uses balanced transmission lines / fast pulses
+
+% FIXME NCR Group patent US4593384A mentioned tamper traces in 1984
+% FIXME NCR Group patent US3594770A mentions meshes in 1968
+% FIXME US110362A from 1870 may be oldes mention of mesh I found
+% FIXME US708093A from 1902 shows literal meshes like we do them today, just with wires not PCBs, and also describes
+% bridge-like comparator circuit using counter-wound coils
+% FIXME Hughes Aircraft patent US5568124A mentions mesh-like panels in 1993
+
+% NOTE: US3882324A mentions exploding the device as tamper response
+
 \subsection{Other Tamper Sensing Techniques}
 
-\subsection{Hardware Security Module Applications}
+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
+sensors have been proposed, including humidity sensors, vibration sensors, light sensors, magnetometers, and radiation
+sensors such as X-ray sensors have been proposed. While the implementation cost of most sensor types is low, each
+additional environmental sensor comes with an increased false alarm rate. Anecdotally, we have heard of light sensors
+being removed from a datacenter HSM product because they caused frequent false alarms despite extensive efforts like
+custom injection-molded plastic light baffles at all air vents of the device designed to prevent ingress of outside
+light.
+% FIXME citations?
 
 \subsection{The Patent Landscape}
 
@@ -154,6 +203,22 @@ their designs. While most original tamper sensing mesh implementations are cover
 highlight IBM for dwarfing the efforts of most other companies and fielding industry's widest portfolio of related
 patents.
 
+While the patent history of HSM-like devices is rather shallow and begins in the 1990ies
+% FIXME cite
+with scarce prior examples,
+% FIXME cite
+tamper-sensing meshes have a much longer history dating back to at least 1870.
+% FIXME cite
+Tamper-sensing meshes were often called \emph{wire coverings} in earlier patent literature from before the widespread
+adoption of printed circuits. Beginning in the late 1800s, there is an abundance of patents claiming such meshes for the
+protection of safes and vault rooms.
+A 1969 NCR patent
+% FIXME cite US10321589B2
+is the earliest mention we were able to find of such a tamper-sensing mesh being implemented in a printed circuit
+process instead of by laying out a physical wire.
+
+\subsection{Hardware Security Module Applications}
+
 \section{A Survey of Meshes in the Wild}
 
 Concluding the brief history of tamper sensing meshes above, we find that they were initially developed for sensitive