62 lines
5.2 KiB
TeX
62 lines
5.2 KiB
TeX
\chapterquote{Phillip Rogaway~\cite{rogawayMoralCharacterCryptographic2015}}{
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Cryptography rearranges power: it configures who can do what, from what. This makes cryptography an inherently
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political tool, and it confers on the field an intrinsically moral dimension.}
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\chapter{Conclusion}
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In this thesis, we propose Inertial Hardware Security Modules (IHSMs), a new approach to physical security that combines
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conventional tamper-sensing meshes with physical movement to bootstrap a highly secure system from low-security,
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off-the-shelf parts, solving our first research question introduced in Chapter~\ref{chapter-intro}. To motivate our
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research, we use the German national digital health record system as an example demonstrating the difficulties in
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achieving useful hardware security in practice. Besides some minor cryptographic oddities, our analysis reveals at least
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one essential specification mistake that negates the hardware security of the system by unnecessarily introducing a
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poorly protected HSM. With this motivation in mind, we support the construction of concretely secure IHSMs by providing
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deep analyses of two key engineering challenges in IHSM construction, mesh monitoring and power transfer. Solving our
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second research question, we propose a low-cost TDR-based mesh monitoring system that exceeds the capabilities of
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previous systems from academic or from patent literature. Our system is capable of monitoring large meshes while
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simultaneously providing detailed results. Our TDR-based mesh monitoring system is of independent interest, since it can
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also be integrated into traditional HSM designs. We additionally propose a new, generalized design for high-frequency
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PCB inductors with low parasitic capacitance. Our design provides better bandwidth and lower parasitic capacitance
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compared to the state of the art without increasing implementation cost. We conclude this thesis with two chapters
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elaborating on two new use cases that are made possible by IHSM technology due to its ability to protect large payloads
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that have high power consumption. Together, these results answer our third and final research question.
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The research presented in this thesis is aimed at advancing both academic research and applied engineering in hardware
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security. We believe that by publishing our research including its artifacts under open source licenses, we provide the
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basis for future research in tamper-sensing technology, a field that remains under-served in today's academic landscape.
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Recent history has shown that state-level adversaries are a mounting threat to civil rights organizations, human rights
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lawyers, members of minorities, and many others. While western democracies used to be considered safe havens of human
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rights, today human rights are under attack both from within and from the outside in countries across the globe.
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Publishing IHSM technology as open source, we hope to provide one building block for new computing systems accessible to
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all that are resilient and secure in the face of growing adversity.
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\section*{Outlook}
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With the research contributions we presented in this thesis, we open up a new field of hardware security research
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centered on Inertial HSMs and improvements to conventional tamper sensing meshes. Below, we will list some research
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directions that we consider worthwhile for future investigation.
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\begin{itemize}
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\item Improving the resolution of the sampling mesh monitoring approach we presented in
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Chapter~\ref{chapter_sampling_mesh_mon}. Possible improvements include increasing pulse risetime through a discrete
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transistor amplifier circuit, as well as evaluating an FPGA as a replacement for the microcontroller to take
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advantage of the improved delay primitives offered by many FPGA families.
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\item Characterizing the PUF-like effects we observed in Chapter~\ref{chapter_sampling_mesh_mon} in mesh coupons using
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our sampling mesh monitoring approach.
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\item Integrating IHSM technology with a HSM firmware implementation into a small form factor to create a portable IHSM.
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A small form factor introduces new challenges besides the mere integration of the necessary circuitry and placement
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of the mesh. For instance, wireless power and data transfer would need to be integrated with the device without
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disrupting mesh monitoring. An on-axis solution would likely require magnetic shielding materials and possible
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non-magnetic ceramic bearings. Furthermore, integrating a sufficiently small motor and optimizing the design for
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long bearing life is challenging at the high rotation speed necessary at a small overall diameter. Finally, at high
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speeds, precisely balancing the whole assembly to avoid vibrations that could lead to early mechanical failure is
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difficult.
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\item Exploring IHSM applications beyond what we outlined in this thesis. For instance, one application of recent
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interests would be physically securing GPUs used for AI training. The background for such work could be either
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export control motivations, or a concern for security and privacy of user input, training data, or even trained
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weights.
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\end{itemize}
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We will proceed with future research into IHSM applications. We have published our results up to this point as open
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source hardware and software, and we intend to build on these publications.
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